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AndroidSQLiteEssentials
TableofContents
AndroidSQLiteEssentials
Credits
AbouttheAuthors
AbouttheReviewers
www.PacktPub.com
Supportfiles,eBooks,discountoffersandmore
WhySubscribe?
FreeAccessforPacktaccountholders
Preface
Whatthisbookcovers
Whatyouneedforthisbook
Whothisbookisfor
Conventions
Readerfeedback
Customersupport
Downloadingtheexamplecode
Errata
Piracy
Questions
1.EnterSQLite
WhySQLite?
TheSQLitearchitecture
TheSQLiteinterface
TheSQLcompiler
Thevirtualmachine
TheSQLitebackend
Aquickreviewofdatabasefundamentals
WhatisanSQLitestatement?
TheSQLitesyntax
DatatypesinSQLite
Storageclasses
TheBooleandatatype
TheDateandTimedatatype
SQLiteinAndroid
SQLiteversion
Databasepackages
APIs
TheSQLiteOpenHelperclass
TheSQLiteDatabaseclass
ContentValues
Cursor
Summary
2.ConnectingtheDots
Buildingblocks
Adatabasehandlerandqueries
BuildingtheCreatequery
BuildingtheInsertquery
BuildingtheDeletequery
BuildingtheUpdatequery
ConnectingtheUIanddatabase
Summary
3.SharingisCaring
Whatisacontentprovider?
Usingexistingcontentproviders
Whatisacontentresolver?
Creatingacontentprovider
UnderstandingcontentURIs
Declaringourcontractclass
CreatingUriMatcherdefinitions
Implementingthecoremethods
InitializingtheproviderthroughtheonCreate()method
Queryingrecordsthroughthequery()method
Addingrecordsthroughtheinsert()method
Updatingrecordsthroughtheupdate()method
Deletingrecordsthroughthedelete()method
GettingthereturntypeofdatathroughthegetType()method
Addingaprovidertoamanifest
Usingacontentprovider
Summary
4.ThreadCarefully
LoadingdatawithCursorLoader
Loaders
LoaderAPI’ssummary
UsingCursorLoader
Datasecurity
ContentProviderandpermissions
Encryptingcriticaldata
Generaltipsandlibraries
Upgradingadatabase
DatabaseminusSQLstatements
Shippingwithaprepopulateddatabase
Summary
Index
AndroidSQLiteEssentials
AndroidSQLiteEssentialsCopyright©2014PacktPublishing
Allrightsreserved.Nopartofthisbookmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans,withoutthepriorwrittenpermissionofthepublisher,exceptinthecaseofbriefquotationsembeddedincriticalarticlesorreviews.
Everyefforthasbeenmadeinthepreparationofthisbooktoensuretheaccuracyoftheinformationpresented.However,theinformationcontainedinthisbookissoldwithoutwarranty,eitherexpressorimplied.Neithertheauthors,norPacktPublishing,anditsdealersanddistributorswillbeheldliableforanydamagescausedorallegedtobecauseddirectlyorindirectlybythisbook.
PacktPublishinghasendeavoredtoprovidetrademarkinformationaboutallofthecompaniesandproductsmentionedinthisbookbytheappropriateuseofcapitals.However,PacktPublishingcannotguaranteetheaccuracyofthisinformation.
Firstpublished:August2014
Productionreference:1200814
PublishedbyPacktPublishingLtd.
LiveryPlace
35LiveryStreet
BirminghamB32PB,UK.
ISBN978-1-78328-295-1
www.packtpub.com
CoverimagebyPratyushMohanta(<[email protected]>)
CreditsAuthors
SunnyKumarAditya
VikashKumarKarn
Reviewers
AmeyHaldankar
GauravMaru
CommissioningEditor
PramilaBalan
AcquisitionEditor
NikhilKarkal
ContentDevelopmentEditor
RuchitaBhansali
TechnicalEditors
DennisJohn
GauravThingalaya
CopyEditors
RoshniBanerjee
GladsonMonteiro
AdithiShetty
ProjectCoordinator
KrantiBerde
Proofreaders
SimranBhogal
JoannaMcMahon
Indexers
MariammalChettiyar
RekhaNair
Graphics
RonakDhruv
ProductionCoordinator
SaiprasadKadam
CoverWork
SaiprasadKadam
AbouttheAuthorsSunnyKumarAdityahasbeenworkingontheAndroidplatformforthepast4years.HistrystwithAndroidbeganwithhiscollegeproject,andhecontinuedwithhisworkinR&DatHCLInfosystemsLtd.SunnylovestostayuptodatewiththelatesttrendsandpracticesinAndroiddevelopment.ApartfrombuildingAndroidapplications,hewritesatwww.deadmango.com.HeiscurrentlytheheadofAndroiddevelopmentatYamunix.
IwouldliketothankPacktPublishingforthisopportunityandmyfamilyaswellasfriendsfortheirsupport.
VikashKumarKarnisanIIITAllahabadalumnusandanECEstudentwhoseloveforcodedrovehimtowardsthesoftwaredevelopmentfield.HehasworkedwithleadingmultinationalsandiscurrentlyworkingatSamsungResearchInstitute,Bangalore,exploringAndroid.
VikashlikestolearntheintricaciesoftheAndroidframeworkandhelpnewcomersinthisfield.Someofhisapplications,suchasMovtanFishingandComparePictures,canbefoundonthePlayStore.
Iwouldliketothankmyfriendsandfamilyfortheirsupportduringthecourseofwritingthisbook.
AbouttheReviewersAmeyHaldankarisanAndroidenthusiasthookedontheplatformsinceitsearlydays.EquippedwithadegreeinComputerScienceEngineeringfromGIT,Belgaum,heisworkingforHCLInfosystemsLtd.asaSeniorSoftwareEngineer.
Ameyhasbeenworkingontheplatformforthepast3yearsdevelopingseveralapplicationsformajorclientssuchasDomino’s,Galatsaray,HCL,andNokia.
AnoteofthankstothepublishinghouseforconsideringmefortheroleofareviewerforAndroidSQLiteEssentials.
GauravMaruhasaBachelor’sdegreeinComputersfromShah&AnchorKutchhiEngineeringCollege.Since2011,hehasbeenworkingasanAndroidapplicationdeveloperatvariousorganizations,includingIndia’slargestretailsectorcompany.Gauravhasdevelopedvariousapps,includingtheonedevelopedfortheUSA’slargestbookseller(aFortune500company).Hedrinks,eats,andsleepsAndroid.Youcancontacthimat<[email protected]>.
Iwouldliketothankmyfamily,friends,colleagues,andPacktPublishing,whohelpedmepullthisoneoffsuccessfully.Cheers!
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PrefaceAndroidisprobablythebuzzwordofthisdecade.Inashortspan,ithastakenoverthemajorityofthehandsetmarket.Androidisstagedtotakeoverwearables,ourTVrooms,aswellasourcarsthisautumnwiththeAndroidLrelease.WiththefranticpaceatwhichAndroidisgrowing,adeveloperneedstouphisorherskillsetsaswell.Database-orientedapplicationdevelopmentisoneofthekeyskillseverydevelopershouldhave.SQLitedatabaseinapplicationsistheheartofadata-centricproductandkeytobuildinggreatproducts.UnderstandingSQLiteandimplementingtheAndroiddatabasecanbeasteeplearningcurveforsomepeople.Conceptssuchascontentprovidersandloadersaremorecomplextounderstandandimplement.AndroidSQLiteEssentialsequipsdeveloperswithtoolstobuilddatabase-basedAndroidapplicationsinasimplisticmanner.Itiswrittenkeepinginmindthecurrentneedsandbestpracticesbeingfollowedintheindustry.Letusstartourjourney.
WhatthisbookcoversChapter1,EnterSQLite,providesaninsightintoSQLitearchitecture,SQLitebasics,anditsAndroidconnection.
Chapter2,ConnectingtheDots,covershowtoconnectyourdatabasetoAndroidviews.Italsocoverssomeofthebestpracticesoneshouldfollowinordertobuildadatabase-centric/database-enabledapplication.
Chapter3,SharingisCaring,willreflectonhowtoaccessandsharedatainAndroidviacontentprovidersandhowtoconstructacontentprovider.
Chapter4,ThreadCarefully,willguideyouonhowtouseloadersandensuresecurityofdatabaseanddata.ItwillalsoprovideyouwithtipstoexplorealternateapproachestobuildingandusingdatabasesinAndroidapplications.
WhatyouneedforthisbookToefficientlyusethisbook,youwillrequireaworkingsystemwithWindows,Ubuntu,orMacOSpreinstalled.DownloadandsetuptheJavaenvironment;werequirethisfortheIDEofourchoice,Eclipse,torun.DownloadAndroidSDKfromtheAndroiddeveloper’ssiteandAndroidADTpluginforEclipse.Alternatively,youcandownloadtheEclipseADTbundlethatcontainsEclipseSDKandtheADTplugin.YoucanalsotryAndroidStudio;thisIDE,whichjustmovedtobeta,isalsoavailableonthedevelopersite.Makesureyouroperatingsystem,JDK,andIDEareallofeither32bitor64bit.
WhothisbookisforAndroidSQLiteEssentialsisaguidebookforAndroidprogrammerswhowanttoexploreSQLitedatabase-basedAndroidapplications.Thereaderisexpectedtohavealittlebitofhands-onexperienceofAndroidfundamentalbuildingblocksandtheknow-howofIDEandAndroidtools.
ConventionsInthisbook,youwillfindanumberofstylesoftextthatdistinguishbetweendifferentkindsofinformation.Herearesomeexamplesofthesestylesandanexplanationoftheirmeaning.
Codewordsintext,databasetablenames,foldernames,filenames,fileextensions,pathnames,dummyURLs,userinput,andTwitterhandlesareshownasfollows:“ToclosetheCursorobject,theclose()methodcallwillbeused.”
Ablockofcodeissetasfollows:
ContentValuescv=newContentValues();
cv.put(COL_NAME,"johndoe");
cv.put(COL_NUMBER,"12345000");
dataBase.insert(TABLE_CONTACTS,null,cv);
Anycommand-lineinputoroutputiswrittenasfollows:
adbshellSQLite3--version
SQLite3.7.11:API16-19
SQLite3.7.4:API11-15
SQLite3.6.22:API8-10
SQLite3.5.9:API3-7
Newtermsandimportantwordsareshowninbold.Wordsthatyouseeonthescreen,inmenusordialogboxesforexample,appearinthetextlikethis:“GotoAndroidVirtualDeviceManagerfromtheWindowsmenutostarttheemulator.”
NoteWarningsorimportantnotesappearinaboxlikethis.
TipTipsandtricksappearlikethis.
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ErrataAlthoughwehavetakeneverycaretoensuretheaccuracyofourcontent,mistakesdohappen.Ifyoufindamistakeinoneofourbooks—maybeamistakeinthetextorthecode—wewouldbegratefulifyouwouldreportthistous.Bydoingso,youcansaveotherreadersfromfrustrationandhelpusimprovesubsequentversionsofthisbook.Ifyoufindanyerrata,pleasereportthembyvisitinghttp://www.packtpub.com/submit-errata,selectingyourbook,clickingontheerratasubmissionformlink,andenteringthedetailsofyourerrata.Onceyourerrataareverified,yoursubmissionwillbeacceptedandtheerratawillbeuploadedonourwebsite,oraddedtoanylistofexistingerrata,undertheErratasectionofthattitle.Anyexistingerratacanbeviewedbyselectingyourtitlefromhttp://www.packtpub.com/support.
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Chapter1.EnterSQLiteDr.RichardHipp,thearchitectandprimaryauthorofSQLite,explainshowitallbeganinhisinterviewwithTheGuardianpublishedinJune2007:
“IstartedonMay292000.It’sjustoversevenyearsold,”hesays.Hewasworkingonaprojectwhichusedadatabaseserver,butfromtimetotimethedatabasewentoffline.“Thenmyprogramwouldgiveanerrormessagesayingthatthedatabaseisn’tworking,andIgottheblameforthis.SoIsaid,thisisnotademandingapplicationforthedatabase,whydon’tIjusttalkdirectlytothedisk,andbuildanSQLdatabaseenginethatway?Thatwashowitstarted.”
BeforewebeginourjourneyexploringSQLiteinthecontextofAndroid,wewouldliketoinformyouofsomeprerequisites.Thefollowingareverybasicrequirementsandwillrequirelittleeffortfromyou:
YouneedtoensurethattheenvironmentforbuildingAndroidapplicationsisinplace.Whenwesay“environment,”werefertothecombinationofJDKandEclipse,ourIDEchoice,ADTplugins,andAndroidSDKtools.Incasethesearenotinplace,theADTbundle,whichconsistsofIDE,ADTplugins,AndroidSDKtools,andplatformtools,canbedownloadedfromhttp://developer.android.com/sdk/index.html.Thestepsmentionedinthelinkareprettyself-explanatory.ForJDK,youcanvisitOracle’swebsitetodownloadthelatestversionandsetitupathttp://www.oracle.com/technetwork/java/javase/downloads/index.html.YouneedtohaveabasicknowledgeofAndroidcomponentsandhaverunmorethan“HelloWorld”programsonanAndroidemulator.Ifnot,averyaptguideispresentontheAndroiddevelopersitetosetupanemulator.WewouldsuggestyoubecomefamiliarwithbasicAndroidcomponents:Intent,Service,ContentProviders,andBroadcastReceiver.TheAndroiddevelopersitehasgoodrepositoriesofsamplesalongwithdocumentation.Someoftheseareasfollows:
Emulator:http://developer.android.com/tools/devices/index.htmlAndroidbasics:http://developer.android.com/training/basics/firstapp/index.html
Withthesethingsinplace,wecannowstartourforayintoSQLite.
Inthischapter,wewillcoverthefollowing:
WhySQLite?TheSQLitearchitectureAquickreviewofdatabasefundamentalsSQLiteinAndroid
WhySQLite?SQLiteisanembeddedSQLdatabaseengine.ItisusedbyprominentnamessuchasAdobeinAdobeIntegratedRuntime(AIR);Airbus,intheirflightsoftware;PythonshipswithSQLite;PHP;andmanymore.Inthemobiledomain,SQLiteisaverypopularchoiceacrossvariousplatformsbecauseofitslightweightnature.AppleusesitintheiPhoneandGoogleintheAndroidoperatingsystem.
Itisusedasanapplicationfileformat,adatabaseforelectronicgadgets,adatabaseforwebsites,andasanenterpriseRDBMS.WhatmakesSQLitesuchaninterestingchoicefortheseandmanyothercompanies?Let’stakeacloserlookatthefeaturesofSQLitethatmakeitsopopular:
Zero-configuration:SQLiteisdesignedinsuchamannerthatitrequiresnoconfigurationfile.Itrequiresnoinstallationstepsorinitialsetup;ithasnoserverprocessrunningandnorecoverystepstotakeevenifitcrashes.Thereisnoserveranditisdirectlyembeddedinourapplication.Furthermore,noadministratorisrequiredtocreateormaintainaDBinstance,orsetpermissionsforusers.Inshort,thisisatrueDBA-lessdatabase.No-copyright:SQLite,insteadofalicense,comeswithablessing.ThesourcecodeofSQLiteisinthepublicdomain;youarefreetomodify,distribute,andevensellthecode.Eventhecontributorsareaskedtosignanaffidavittoprotectfromanycopyrightswarfarethatmayoccurinfuture.Cross-platform:Databasefilesfromonesystemcanbemovedtoasystemrunningadifferentarchitecturewithoutanyhassle.Thisispossiblebecausethedatabasefileformatisbinaryandallthemachinesusethesameformat.Inthefollowingchapters,wewillbepullingoutadatabasefromanAndroidemulatortoWindows.Compact:AnSQLitedatabaseisasingleordinarydiskfile;itcomeswithoutaserverandisdesignedtobelightweightandsimple.Theseattributesleadtoaverylightweightdatabaseengine.SQLiteVersion3.7.8hasafootprintoflessthan350KiB(kibibyte)comparedtoitsotherSQLdatabaseengines,whicharemuchlarger.Foolproof:Thecodebaseiswellcommented,easytounderstand,andmodular.ThetestcasesandtestscriptsinSQLitehaveapproximately1084timesmorecodethanthesourcecodeofSQLitelibraryandtheyclaim100percentbranchtestcoverage.ThisleveloftestingreaffirmsthefaithinstilledinSQLitebydevelopers.
NoteInterestedreaderscanreadmoreaboutbranchtestcoveragefromWikipediaathttp://en.wikipedia.org/wiki/Code_coverage.
TheSQLitearchitectureThecore,SQLcompiler,backend,anddatabaseformtheSQLitearchitecture:
TheSQLiteinterfaceAtthetopoftheSQLitelibrarystack,accordingtodocumentation,muchofthepublicinterfacetotheSQLitelibraryisimplementedbythewen.c,legacy.c,andvdbeapi.csourcefiles.Thisisthepointofcommunicationforotherprogramsandscripts.
TheSQLcompilerTokenizerbreakstheSQLstringpassedfromtheinterfaceintotokensandhandsthetokensovertotheparser,onebyone.Tokenizerishand-codedinC.TheparserforSQLiteisgeneratedbytheLemonparsergenerator.ItisfasterthanYACCandBisonand,atthesametime,isthreadsafeandpreventsmemoryleaks.Theparserbuildsaparsetreefromthetokenspassedbythetokenizerandpassesthetreetothecodegenerator.Thegeneratorproducesvirtualmachinecodefromtheinputandpassesittothevirtualmachineasexecutables.MoreinformationabouttheLemonparsergeneratorcanbefoundathttp://en.wikipedia.org/wiki/Lemon_Parser_Generator.
ThevirtualmachineThevirtualmachine,alsoknownasVirtualDatabaseEngine(VDBE),istheheartofSQLite.Itisresponsibleforfetchingandchangingvaluesinthedatabase.Itexecutestheprogramgeneratedbythecodegeneratortomanipulatedatabasefiles.EachSQLstatementisfirstconvertedintovirtualmachinelanguageforVDBE.EachinstructionofVDBEcontainsanopcodeanduptothreeadditionaloperands.
TheSQLitebackendB-trees,alongwithPagerandtheOSInterface,formthebackendoftheSQLitearchitecture.B-treesareusedtoorganizethedata.ThepagerontheotherhandassistsB-treebycaching,modifying,androllingbackdata.B-tree,whenrequired,requestsparticularpagesfromthecache;thisrequestisprocessedbythepagerinanefficientandreliablemanner.TheOSInterface,asthenamesuggests,providesanabstractionlayertoporttodifferentoperatingsystems.IthidestheunnecessarydetailsofcommunicatingwithdifferentoperatingsystemsfromSQLitecallsandhandlesthemonbehalfofSQLite.
ThesearetheinternalsofSQLiteandanapplicationdeveloperinAndroidneednotworryabouttheinternalsofAndroidbecausetheSQLiteAndroidlibrarieshaveeffectivelyusedtheconceptofabstractionandallthecomplexitiesarehidden.OnejustneedstomastertheAPIsprovided,andthatwillcatertoallthepossibleusecasesofSQLiteinanAndroidapplication.
AquickreviewofdatabasefundamentalsAdatabase,insimplewords,isanorganizedwaytostoredatainacontinualfashion.Dataissavedintables.Atableconsistsofcolumnswithdifferentdatatypes.Everyrowinatablecorrespondstoadatarecord.YoumaythinkofatableasanExcelspreadsheet.Fromtheperspectiveofobject-orientedprogramming,everytableinadatabaseusuallydescribesanobject(representedbyaclass).Eachtablecolumnillustratesaclassattribute.Everyrecordinatablerepresentsaparticularinstanceofthatobject.
Let’slookataquickexample.Let’sassumeyouhaveaShopdatabasewithatablecalledInventory.Thistablemightbeusedtostoretheinformationaboutalltheproductsintheshops.TheInventorytablemightcontainthesecolumns:Productname(string),ProductId(number),Cost(number),Instock(0/1),andNumbersavailable(number).YoucouldthenaddarecordtothedatabaseforaproductnamedShoe:
ID Productname ProductId Cost Instock Numbersavailable
1 Carpet 340023 2310 1 4
2 Shoe 231257 235 1 2
Datainthedatabaseissupposedtobecheckedandinfluenced.Thedatawithinatablecanbeasfollows:
Added(withtheINSERTcommand)Modified(withtheUPDATEcommand)Removed(withtheDELETEcommand)
Youmaysearchforparticulardatawithinadatabasebyutilizingwhatisknownasaquery.Aquery(usingtheSELECTcommand)caninvolveonetable,oranumberoftables.Togenerateaquery,youmustdeterminethetables,datacolumns,andvaluesofthedataofinterestusingSQLcommands.EachSQLcommandisconcludedwithasemicolon(;).
WhatisanSQLitestatement?AnSQLitestatementiswritteninSQL,whichisissuedtoadatabasetoretrievedataortocreate,insert,update,ordeletedatainthedatabase.
AllSQLitestatementsstartwithanyofthekeywords:SELECT,INSERT,UPDATE,DELETE,ALTER,DROP,andsoon,andallthestatementsendwithasemicolon(;).Forinstance:
CREATETABLEtable_name(column_nameINTEGER);
TheCREATETABLEcommandisusedtocreateanewtableinanSQLitedatabase.ACREATETABLEcommanddescribesthefollowingattributesofthenewtablethatisbeingcreated:
Thenameofthenewtable.Thedatabaseinwhichthenewtableiscreated.Tablesmaybegeneratedinthemaindatabase,thetempdatabase,orinanydatabaseattached.Thenameofeachcolumninthetable.Thedeclaredtypeofeachcolumninthetable.Adefaultvalueorexpressionforeachcolumninthetable.Adefaultrelationsequencetobeusedwitheachcolumn.Preferably,aPRIMARYKEYforthetable.Thiswillsupportbothsingle-columnandcomposite(multiple-column)primarykeys.AsetofSQLconstraintsforeachtable.ConstraintssuchasUNIQUE,NOTNULL,CHECK,andFOREIGNKEYaresupported.Insomecases,thetablewillbeaWITHOUTROWIDtable.
ThefollowingisasimpleSQLitestatementtocreateatable:
StringdatabaseTable="CREATETABLE"
+TABLE_CONTACTS+"("
+KEY_ID
+"INTEGERPRIMARYKEY,"
+KEY_NAME+"TEXT,"
+KEY_NUMBER+"INTEGER"
+")";
Here,CREATETABLEisthecommandtocreateatablewiththenameTABLE_CONTACTS.KEY_ID,KEY_NAMEandKEY_NUMBERarethecolumnIDs.SQLiterequiresauniqueIDtobeprovidedforeachcolumn.INTEGERandTEXTarethedatatypesassociatedwiththecorrespondingcolumns.SQLiterequiresthetypeofdatatobestoredinacolumntobedefinedatthetimeofcreationofthetable.PRIMARYKEYisthedatacolumnconstraint(rulesenforcedondatacolumnsinthetable).
SQLitesupportsmoreattributesthatcanbeusedforcreatingatable,forinstance,letuscreateacreatetablestatementthatinputsadefaultvalueforemptycolumns.NoticethatforKEY_NAME,weareprovidingadefaultvalueasxyzandfortheKEY_NUMBERcolumn,weareprovidingadefaultvalueof100:
StringdatabaseTable=
"CREATETABLE"
+TABLE_CONTACTS+"("
+KEY_ID+"INTEGERPRIMARYKEY,"
+KEY_NAME+"TEXTDEFAULTxyz,"
+KEY_NUMBER+"INTEGERDEFAULT100"+")";
Here,whenarowisinsertedinthedatabase,thesecolumnswillbepreinitializedwiththedefaultvaluesasdefinedintheCREATESQLstatement.
Therearemorekeywords,butwedon’twantyoutogetboredwithahugelist.Wewillbecoveringotherkeywordsinthesubsequentchapters.
TheSQLitesyntaxSQLitefollowsauniquesetofrulesandguidelinescalledsyntax.
AnimportantpointtobenotedisthatSQLiteiscase-insensitive,buttherearesomecommandsthatarecase-sensitive,forexample,GLOBandglobhavedifferentmeaninginSQLite.LetuslookattheSQLiteDELETEstatement’ssyntaxforinstance.Althoughwehaveusedcapitalletters,replacingthemwithlowercaseletterswillalsoworkfine:
DELETEFROMtableWHERE{condition};
DatatypesinSQLiteSQLiteusesadynamicandweaklytypedSQLsyntax,whereasmostoftheSQLdatabasesusestatic,rigidtyping.Ifwelookatotherlanguages,JavaisastaticallytypedlanguageandPythonisadynamicallytypedlanguage.Sowhatdowemeanwhenwesaydynamicorstatic?Letuslookatanexample:
a=5
a="android"
Instaticallytypedlanguages,thiswillthrowanexception,whereasinadynamicallytypedlanguageitwillwork.InSQLite,thedatatypeofavalueisnotassociatedwithitscontainer,butwiththevalueitself.Thisisnotacauseofconcernwhendealingwithstaticallytypedsystems,whereavalueisdeterminedbyacontainer.ThisisbecauseSQLiteisbackwardscompatiblewiththemorecommonstatictypesystems.Hence,theSQLstatementsthatweuseforstaticsystemscanbeusedseamlesslyhere.
StorageclassesInSQLite,wehavestorageclassesthataremoregeneralthandatatypes.Internally,SQLitestoresdatainfivestorageclassesthatcanalsobereferredtoasprimitivedatatypes:
NULL:Thisrepresentsamissingvaluefromthedatabase.INTEGER:Thissupportsarangeofsignedintegersfrom1,2,3,4,6,or8bytesdependingonthemagnitudeofthevalue.SQLitehandlesthisautomaticallybasedonthevalue.Atthetimeofprocessinginthememory,theyareconvertedtothemostgeneral8-bytesignedintegerform.REAL:Thisisafloatingpointvalue,andSQLiteusesthisasan8-byteIEEEfloatingpointnumbertostoresuchvalues.TEXT:SQLitesupportsvariouscharacterencodings,suchasUTF-8,UTF-16BE,orUTF-16LE.Thisvalueisatextstring.BLOB:Thistypestoresalargearrayofbinarydata,exactlyhowitwasprovidedasinput.
SQLiteitselfdoesnotvalidateifthetypeswrittentothecolumnsareactuallyofthedefinedtype,forexample,youcanwriteanintegerintoastringcolumnandviceversa.Wecanevenhaveasinglecolumnwithdifferentstorageclasses:
idcol_t
------------
123
2NULL
3test
TheBooleandatatypeSQLitedoesnothaveaseparatestorageclassforBooleanandusestheIntegerclassforthispurpose.Integer0representsthefalsestatewhereas1representsatruestate.ThismeansthatthereisanindirectsupportforBooleanandwecancreateBooleantype
columnsonly.Thecatchis,itwon’tcontainthefamiliarTRUE/FALSEvalues.
TheDateandTimedatatypeAswesawfortheBooleandatatype,thereisnostorageclassfortheDateandTimedatatypesinSQLite.SQLitehasfivebuilt-indateandtimefunctionstohelpuswithit;wecanusedateandtimeasinteger,text,orrealvalues.Moreover,thevaluesareinterchangeable,dependingontheneedoftheapplication.Forexample,tocomputethecurrentdate,usethefollowingcode:
SELECTdate('now');
SQLiteinAndroidTheAndroidsoftwarestackconsistsofcoreLinuxkernel,Androidruntime,AndroidlibrariesthatsupporttheAndroidframework,andfinallyAndroidapplicationsthatrunontopofeverything.TheAndroidruntimeusesDalvikvirtualmachine(DVM)toexecutethedexcode.InnewerversionsofAndroid,thatis,fromKitKat(4.4),AndroidhasenabledanexperimentalfeatureknownasART,whichwilleventuallyreplaceDVM.ItisbasedonAheadofTime(AOT),whereasDVMisbasedonJustinTime(JIT).Inthefollowingdiagram,wecanseethatSQLiteprovidesnativedatabasesupportandispartofthelibrariesthatsupporttheapplicationframeworkalongwithlibrariessuchasSSL,OpenGLES,WebKit,andsoon.Theselibraries,writteninC/C++,runovertheLinuxkerneland,alongwiththeAndroidruntime,formsthebackboneoftheapplicationframework,asshowninthefollowingdiagram:
BeforewestartexploringSQLiteinAndroid,let’stakealookattheotherpersistentstoragealternativesinAndroid:
Sharedpreference:Dataisstoredinasharedpreferenceinthekey-valueform.ThefileitselfisanXMLfilecontainingthekey-valuepairs.Thefileispresentinthe
internalstorageofanapplication,andaccesstoitcanbepublicorprivateasneeded.AndroidprovidesAPIstowriteandreadsharedpreferences.Itisadvisedtousethisincasewehavetosaveasmallcollectionofsuchdata.AgeneralexamplewouldbesavingthelastreadpositioninaPDF,orsavingauser’spreferencetoshowaratingbox.Internal/externalstorage:Thisterminologycanbealittlemisleading;Androiddefinestwostoragespacestosavefiles.Onsomedevices,youmighthaveanexternalstoragedeviceinformofanSDcard,whereasonothers,youwillfindthatthesystemhaspartitioneditsmemoryintotwoparts,tobelabeledasinternalandexternal.PathstotheexternalaswellasinternalstoragecanbefetchedbyusingAndroidAPIs.Internalstorage,bydefault,islimitedandaccessibleonlytotheapplication,whereastheexternalstoragemayormaynotbeavailableincaseitismounted.
Tipandroid:installLocationcanbeusedinthemanifesttospecifytheinternal/externalinstallationlocationofanapplication.
SQLiteversionSinceAPIlevel1,AndroidshipswithSQLite.Atthetimeofwritingthisbook,thecurrentversionofSQLitewas3.8.4.1.Accordingtothedocumentation,theversionofSQLiteis3.4.0,butdifferentAndroidversionsareknowntoshipwithdifferentversionsofSQLite.WecaneasilyverifythisviatheuseofatoolcalledSQLite3presentintheplatform-toolsfolderinsidetheAndroidSDKinstallationfolderandAndroidEmulator:
adbshellSQLite3--version
SQLite3.7.11:API16-19
SQLite3.7.4:API11-15
SQLite3.6.22:API8-10
SQLite3.5.9:API3-7
WeneednotworryaboutthedifferentversionsofSQLiteandshouldstickto3.5.9forcompatibility,orwecangobythesayingthatAPI14isthenewminSdkVersionandswitchitwith3.7.4.Untilandunlessyouhavesomethingveryspecifictoaparticularversion,itwillhardlymatter.
NoteSomeadditionalhandySQLite3commandsareasfollows:
.dump:Toprintoutthecontentsofatable
.schema:ToprinttheSQLCREATEstatementforanexistingtable
.help:Forinstructions
DatabasepackagesTheandroid.databasepackagecontainsallthenecessaryclassesforworkingwithdatabases.Theandroid.database.SQLitepackagecontainstheSQLite-specificclasses.
APIsAndroidprovidesvariousAPIstoenableustocreate,access,modify,anddeleteadatabase.Thecompletelistcanbequiteoverwhelming;forthesakeofbrevity,wewillcoverthemostimportantandusedones.
TheSQLiteOpenHelperclassTheSQLiteOpenHelperclassisthefirstandmostessentialclassofAndroidtoworkwithSQLitedatabases;itispresentintheandroid.database.SQLitenamespace.SQLiteOpenHelperisahelperclassthatisdesignedforextensionandtoimplementthetasksandactionsyoudeemimportantwhencreating,opening,andusingadatabase.ThishelperclassisprovidedbytheAndroidframeworktoworkwiththeSQLitedatabaseandhelpsinmanagingthedatabasecreationandversionmanagement.Themodusoperandiwouldbetoextendtheclassandimplementtasksandactionsasrequiredbyourapplication.SQLiteOpenHelperhasconstructorsdefinedasfollows:
SQLiteOpenHelper(Contextcontext,Stringname,SQLiteDatabase.CursorFactory
factory,intversion)
SQLiteOpenHelper(Contextcontext,Stringname,SQLiteDatabase.CursorFactory
factory,intversion,DatabaseErrorHandlererrorHandler)
Theapplicationcontextpermitsaccesstoallthesharedresourcesandassetsfortheapplication.ThenameparameterconsistsofthedatabasefilenameintheAndroidstorage.SQLiteDatabase.CursorFactoryisafactoryclassthatcreatescursorobjectsthatactastheoutputsetforallthequeriesyouapplyagainstSQLiteunderAndroid.Theapplication-specificversionnumberforthedatabasewillbetheversionparameter(ormoreparticularly,itsschema).
TheconstructorofSQLiteOpenHelperisusedtocreateahelperobjecttocreate,open,ormanageadatabase.Thecontextistheapplicationcontextthatallowsaccesstoallthesharedresourcesandassets.Thenameparametereithercontainsthenameofadatabaseornullforanin-memorydatabase.TheSQLiteDatabase.CursorFactoryfactorycreatesacursorobjectthatactsastheresultsetforallthequeries.Theversionparameterdefinestheversionnumberofthedatabaseandisusedtoupgrade/downgradethedatabase.TheerrorHandlerparameterinthesecondconstructorisusedwhenSQLitereportsdatabasecorruption.
SQLiteOpenHelperwilltriggeritsonUpgrade()methodifourdatabaseversionnumberisnotatdefault1.ImportantmethodsoftheSQLiteOpenHelperclassareasfollows:
synchronizedvoidclose()
synchronizedSQLiteDatabasegetReadableDatabase()
synchronizedSQLiteDatabasegetWritableDatabase()
abstractvoidonCreate(SQLiteDatabasedb)
voidonOpen(SQLiteDatabasedb)
abstractvoidonUpgrade(SQLiteDatabasedb,intoldVersion,int
newVersion)
Thesynchronizedclose()methodclosesanyopendatabaseobject.Thesynchronizedkeywordpreventsthreadandmemoryconsistencyerrors.
Thenexttwomethods,getReadableDatabase()andgetWriteableDatabase(),arethemethodsinwhichthedatabaseisactuallycreatedoropened.BothreturnthesameSQLiteDatabaseobject;thedifferenceliesinthefactthatgetReadableDatabase()willreturnareadabledatabaseincaseitcannotreturnawritabledatabase,whereasgetWriteableDatabase()returnsawritabledatabaseobject.ThegetWriteableDatabase()methodwillthrowanSQLiteExceptionifadatabasecannotbeopenedforwriting.IncaseofgetReadableDatabase(),ifadatabasecannotbeopened,itwillthrowthesameexception.
WecanusetheisReadOnly()methodoftheSQLiteDatabaseclassonthedatabaseobjecttoknowthestateofthedatabase.Itreturnstrueforread-onlydatabases.
CallingeithermethodswillinvoketheonCreate()methodifthedatabasedoesn’texistyet.Otherwise,itwillinvoketheonOpen()oronUpgrade()methods,dependingontheversionnumber.TheonOpen()methodshouldchecktheisReadOnly()methodbeforeupdatingthedatabase.Onceopened,thedatabaseiscachedtoimproveperformance.Finally,weneedtocalltheclose()methodtoclosethedatabaseobject.
TheonCreate(),onOpen(),andonUpgrade()methodsaredesignedforthesubclasstoimplementtheintendedbehavior.TheonCreate()methodiscalledwhenthedatabaseiscreatedforthefirsttime.ThisistheplacewherewecreateourtablesbyusingSQLitestatements,whichwesawearlierintheexample.TheonOpen()methodistriggeredwhenthedatabasehasbeenconfiguredandafterthedatabaseschemahasbeencreated,upgraded,ordowngradedasnecessary.Read/writestatusshouldbecheckedherewiththehelpoftheisReadOnly()method.
TheonUpgrade()methodiscalledwhenthedatabaseneedstobeupgradeddependingontheversionnumbersuppliedtoit.Bydefault,thedatabaseversionis1,andasweincrementthedatabaseversionnumbersandreleasenewversions,theupgradewillbeperformed.
AsimpleexampleillustratingtheuseoftheSQLiteOpenHelperclassispresentinthecodebundleforthischapter;wewouldbeusingitforexplanation:
classSQLiteHelperClass
{
...
...
publicstaticfinalintVERSION_NUMBER=1;
sqlHelper=
newSQLiteOpenHelper(context,"ContactDatabase",null,
VERSION_NUMBER)
{
@Override
publicvoidonUpgrade(SQLiteDatabasedb,
intoldVersion,intnewVersion)
{
//droptableonupgrade
db.execSQL("DROPTABLEIFEXISTS"
+TABLE_CONTACTS);
//Createtablesagain
onCreate(db);
}
@Override
publicvoidonCreate(SQLiteDatabasedb)
{
//creatingtableduringonCreate
StringcreateContactsTable=
"CREATETABLE"
+TABLE_CONTACTS+"("
+KEY_ID+"INTEGERPRIMARYKEY,"
+KEY_NAME+"TEXT,"
+KEY_NUMBER+"INTEGER"+")";
try{
db.execSQL(createContactsTable);
}catch(SQLExceptione){
e.printStackTrace();
}
}
@Override
publicsynchronizedvoidclose()
{
super.close();
Log.d("TAG","Databaseclosed");
}
@Override
publicvoidonOpen(SQLiteDatabasedb)
{
super.onOpen(db);
Log.d("TAG","Databaseopened");
}
};
...
...
//openthedatabaseinread-onlymode
SQLiteDatabasedb=SQLiteOpenHelper.getWritableDatabase();
...
...
//openthedatabaseinread/writemode
SQLiteDatabasedb=SQLiteOpenHelper.getWritableDatabase();
TipDownloadingtheexamplecode
YoucandownloadtheexamplecodefilesforallPacktbooksyouhavepurchasedfromyouraccountathttp://www.packtpub.com.Ifyoupurchasedthisbookelsewhere,youcanvisithttp://www.packtpub.com/supportandregistertohavethefilese-maileddirectlytoyou.
TheSQLiteDatabaseclassNowthatyouarefamiliarwiththehelperclassthatkick-startstheuseofSQLitedatabaseswithinAndroid,it’stimetolookatthecoreSQLiteDatabaseclass.SQLiteDatabaseisthebaseclassrequiredtoworkwithanSQLitedatabaseinAndroidandprovidesmethodstoopen,query,update,andclosethedatabase.
Morethan50methodsareavailablefortheSQLiteDatabaseclass,eachwithitsownnuancesandusecases.Ratherthananexhaustivelist,we’llcoverthemostimportantsubsetsofmethodsandallowyoutoexploresomeoftheoverloadedmethodsatyourleisure.Atanytime,youcanrefertothefullonlineAndroiddocumentationfortheSQLiteDatabaseclassathttp://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html.
SomemethodsoftheSQLiteDatabaseclassareshowninthefollowinglist:
publiclonginsert(Stringtable,StringnullColumnHack,ContentValues
values)
publicCursorquery(Stringtable,String[]columns,Stringselection,
String[]selectionArgs,StringgroupBy,Stringhaving,StringorderBy)
publicCursorrawQuery(Stringsql,String[]selectionArgs)
publicintdelete(Stringtable,StringwhereClause,String[]
whereArgs)
publicintupdate(Stringtable,ContentValuesvalues,String
whereClause,String[]whereArgs)
LetusseetheseSQLiteDatabaseclassesinactionwithanexample.Wewillinsertanameandnumberinourtable.Thenwewillusetherawquerytofetchdatabackfromthetable.Afterthis,wewillgothroughthedelete()andupdate()methods,bothofwhichwilltakeidasaparametertoidentifywhichrowofdatainourdatabasetableweintendtodeleteorupdate:
publicvoidinsertToSimpleDataBase()
{
SQLiteDatabasedb=sqlHelper.getWritableDatabase();
ContentValuescv=newContentValues();
cv.put(KEY_NAME,"John");
cv.put(KEY_NUMBER,"0000000000");
//Insertingvaluesindifferentcolumnsofthetableusing
//ContentValues
db.insert(TABLE_CONTACTS,null,cv);
cv=newContentValues();
cv.put(KEY_NAME,"Tom");
cv.put(KEY_NUMBER,"5555555");
//Insertingvaluesindifferentcolumnsofthetableusing
//ContentValues
db.insert(TABLE_CONTACTS,null,cv);
}
...
...
publicvoidgetDataFromDatabase()
{
intcount;
db=sqlHelper.getReadableDatabase();
//Useofnormalquerytofetchdata
Cursorcr=db.query(TABLE_CONTACTS,null,null,
null,null,null,null);
if(cr!=null){
count=cr.getCount();
Log.d("DATABASE","countis:"+count);
}
//Useofrawquerytofetchdata
cr=db.rawQuery("select*from"+TABLE_CONTACTS,null);
if(cr!=null){
count=cr.getCount();
Log.d("DATABASE","countis:"+count);
}
}
...
...
publicvoiddelete(Stringname)
{
StringwhereClause=KEY_NAME+"=?";
String[]whereArgs=newString[]{name};
db=sqlHelper.getWritableDatabase();
introwsDeleted=db.delete(TABLE_CONTACTS,whereClause,whereArgs);
}
...
...
publicvoidupdate(Stringname)
{
StringwhereClause=KEY_NAME+"=?";
String[]whereArgs=newString[]{name};
ContentValuescv=newContentValues();
cv.put(KEY_NAME,"Betty");
cv.put(KEY_NUMBER,"999000");
db=sqlHelper.getWritableDatabase();
introwsUpdated=db.update(TABLE_CONTACTS,cv,whereClause,
whereArgs);
}
ContentValuesContentValuesisessentiallyasetofkey-valuepairs,wherethekeyrepresentsthecolumnforthetableandthevalueisthevaluetobeinsertedinthatcolumn.So,inthecaseofvalues.put("COL_1",1);,thecolumnisCOL_1andthevaluebeinginsertedforthatcolumnis1.
Thefollowingisanexample:
ContentValuescv=newContentValues();
cv.put(COL_NAME,"johndoe");
cv.put(COL_NUMBER,"12345000");
dataBase.insert(TABLE_CONTACTS,null,cv);
CursorAqueryrecoversaCursorobject.ACursorobjectdepictstheresultofaqueryandfundamentallypointstoonerowoftheresultofthequery.Withthismethod,Androidcanbuffertheresultsofthequeryinaproductivemanner;asitdoesn’tneedtoloadallofthedataintomemory.
Toobtaintheelementsoftheresultingquery,youcanusethegetCount()method.
Tonavigateamidindividualdatarows,youcanutilizethemoveToFirst()andmoveToNext()methods.TheisAfterLast()methodpermitsyoutoanalyzewhethertheendoftheoutputhasarrived.
TheCursorobjectprovidestypedget*()methods,forexample,thegetLong(columnIndex)andgetString(columnIndex)methodstogainentrytothecolumndatafortheongoingpositionoftheresult.columnIndexisthenumberofthecolumnyouwillbeaccessing.
TheCursorobjectalsoprovidesthegetColumnIndexOrThrow(String)methodthatpermitsyoutogetthecolumnindexforacolumnnameofthetable.
ToclosetheCursorobject,theclose()methodcallwillbeused.
Adatabasequeryreturnsacursor.Thisinterfaceprovidesrandomread-writeaccesstotheresultset.ItpointstoarowofthequeryresultthatenablesAndroidtobuffertheresultseffectivelysincenowitisnotrequiredtoloadallthedatainthememory.
Thepointerofthereturnedcursorpointstothe0thlocation,whichisknownasthefirstlocationofthecursor.WeneedtocallthemoveToFirst()methodontheCursorobject;ittakesthecursorpointertothefirstlocation.Nowwecanaccessthedatapresentinthefirstrecord.
Cursorimplementations,iffrommultiplethreads,shouldperformtheirownsynchronizationwhenusingthecursor.Acursorneedstobeclosedtofreetheresourcethe
objectholdsbycallingtheclose()method.
Someothersupportmethodswewillencounterareasfollows:
ThegetCount()method:Thisreturnsthenumbersofelementsintheresultingquery.Theget*()methods:Theseareusedtoaccessthecolumndataforthecurrentpositionoftheresult,forexample,getLong(columnIndex)andgetString(columnIndex).ThemoveToNext()method:Thismovesthecursortothenextrow.Ifthecursorisalreadypastthelastentryintheresultset,itwillreturnfalse.
SummaryWecoveredinthischaptertheknow-howofSQLitefeaturesanditsinternalarchitecture.WestartedwithadiscussiononwhatmakesSQLitesopopularbylookingatitssalientfeatures,thenwecoveredtheunderlyingarchitectureofSQLiteandwentoverdatabasefundamentalssuchassyntaxanddatatypes,andfinallymovedontoSQLiteinAndroid.WeexploredtheAndroidAPIsforusingSQLiteinAndroid.
Inthenextchapter,wewillfocusoncarryingforwardwhatwehavelearnedinthischapterandapplyittobuildAndroidapplications.WewillfocusontheUIelementsandconnectingUItothedatabasecomponents.
Chapter2.ConnectingtheDots “Youdon’tunderstandanythinguntilyoulearnitmorethanoneway.”
—-MarvinMinsky
Inthepreviouschapter,welearnedthetwoimportantAndroidclassesandtheircorrespondingmethodsinordertoworkwithanSQLitedatabase:
TheSQLiteOpenHelperclassTheSQLiteDatabaseclass
Wealsosawcodesnippetsexplainingtheirimplementation.Now,wearereadytousealltheseconceptsinanAndroidapplication.Wewillbeleveragingwhatwelearnedinthepreviouschaptertomakeafunctionalapplication.WewillfurtherlookintotheSQLstatementstoinsert,query,anddeletedatafromadatabase.
Inthischapter,wewillbebuildingandrunninganAndroidapplicationonanAndroidemulator.Wewillalsobebuildingourownfull-fledgedcontactsdatabase.WewillencounterAndroidUIcomponents,suchasButtonsandListView,whileprogressingthroughthischapter.IncasearevisitofUIcomponentsinAndroidisrequired,pleasevisitthelinkhttp://developer.android.com/design/building-blocks/index.html.
Beforewebegin,thecodeinthischapterismeanttoexplaintheconceptsrelatedtoanSQLitedatabaseinAndroidandisnotproductionready;inalotofplaces,youwillfindlackofproperexceptionhandlingorlackofpropernullchecksandsimilarpracticestoreduceverbosityinthecode.YoucandownloadthecompletecodefromPackt’swebsiteforthecurrentandfollowingchapters.Forbestresults,werecommenddownloadingthecodeandreferringtoitaswemovealongthechapter.
Inthischapter,wewillcover:
BuildingblocksDatabasehandlerandqueriesConnectingtheUIanddatabase
BuildingblocksAndroidisknowntorunonavarietyofdeviceswithdifferenthardwareandsoftwarespecifications.Atthetimeofwritingthisbook,1billionactivationmarkshavebeencrossed.ThenumberofdevicesrunningAndroidisstaggering,providinguserswitharichvarietyofoptionsindifferentformfactorsandondifferenthardwarebases.Thisaddsaroadblockwhenitcomestotestingyourapplicationondifferentdevices,becauseitishumanlyimpossibletogetholdofthemall,nottoforgetthetimeandcapitalneededtobeinvestedinit.Emulatorinitselfisagreattool;itenablesustocircumventthisproblembygivingustheflexibilitytomimicdifferenthardwarefeatures,suchasCPUarchitecture,RAM,andcamera,anddifferentsoftwareversionsrangingfromearlyCupcaketoKitKat.Wewillalsotrytoleveragethistoouradvantageinourprojectandtrytorunourapplicationontheemulator.Anaddedbenefitofusingtheemulatoristhatwewillberunningarooteddevicethatwillallowustoperformsomeactions.Wewillnotbeabletoachievetheseactionsonanormaldevice.
Let’sstartbysettingupanemulatorinEclipse:
1. GotoAndroidVirtualDeviceManagerfromtheWindowmenutostarttheemulator.
WecansetdifferenthardwarepropertiessuchastheCPUtype,front/backcamera,RAMpreferablylessthan768MBonaWindowsmachine,internal,andexternalstoragesize.
2. Whilelaunchingtheapp,enableSavetosnapshot;thiswillreducethelaunchtimethenexttimewearelaunchinganemulatorinstancefromthesnapshot:
NoteInterestedreaderswhowanttotryoutafasteremulatorcangiveGenymotionatryathttp://www.genymotion.co.
Let’sstartbuildingourAndroidapplicationnow.
3. WewillstartbycreatinganewprojectPersonalContactManager.GotoFile|New|Project.Now,navigatetoAndroidandthenselectAndroidApplicationProject.ThisstepwillgiveusanactivityfileandacorrespondingXMLfile.
Wewillcomebacktothesecomponentsafterwehavealltheblocksweneedinplace.For
ourapplication,wewillcreateadatabasecalledcontact,whichwillcontainonetable,ContactsTable.Inthepreviouschapter,wewentoverhowtocreateadatabaseusingaSQLstatement;let’sconstructadatabaseschemaforourproject.Thisisaveryimportantstepthatisbasedonourapplication’srequirements;forexample,inourcase,wearebuildingapersonalcontactmanagerandwillrequirefieldssuchasname,number,e-mail,andadisplaypicture.
ThedatabaseschemaforContactsTableisoutlined:
Column Datatype
Contact_ID Integer/primarykey/autoincrement
Name Text
Number Text
Email Text
Photo Blob
NoteAnAndroidapplicationcanhavemorethanonedatabaseandeachdatabasecanhavemorethanonetable.Eachtablestoresdatainthe2D(rowsandcolumns)format.
ThefirstcolumnisContact_ID.Itsdatatypeisintegeranditscolumnconstraintistheprimarykey.Also,thecolumnisautoincremented,whichmeansforeachrowitwillbeincrementedbyonewhendataisinsertedinthatrow.
Theprimarykeyuniquelyidentifieseachrowandcannotbenull.Eachtableinadatabasecanhaveoneprimarykeyatthemost.Theprimarykeyofonetablecanactastheforeignkeyforanothertable.Theforeignkeyservesasaconnectionbetweentworelatedtables;forinstance,ourcurrentContactsTableschemais:
ContactsTable(Contact_ID,Name,Number,Email,Photo)
Let’ssaywehaveanothertableColleagueTablewiththefollowingschema:
ColleagueTable(Colleague_ID,Contact_ID,Position,Fax)
Here,theprimarykeyofContactTable,thatis,Contact_IDcanbetermedasaforeignkeyforColleagueTable.ItservesthepurposeoflinkingtwotablesinarelationaldatabaseandhenceallowsustoperformoperationsonColleagueTable.Wewillexplorethisconceptindetailinthechaptersandexamplesahead.
NoteColumnconstraint
Constraintsaretherulesenforcedondatacolumnsinatable.Thisensurestheaccuracyandreliabilityofdatainthedatabase.
UnlikemostSQLdatabases,SQLitedoesnotrestrictthetypeofdatathatmaybeinsertedintoacolumnbasedonthedeclaredtypeofcolumns.Instead,SQLiteusesdynamictyping.Thedeclaredtypeofacolumnisusedtodeterminetheaffinityofthecolumnonly.Thereisatypeconversionalso(automatically)whenonetypeofvariableisstoredintheother.
Constraintscanbecolumnlevelortablelevel.Column-levelconstraintsareappliedonlytoonecolumn,whereastable-levelconstraintsareappliedtothewholetable.
ThefollowingarethecommonlyusedconstraintsandkeywordsavailableinSQLite:
TheNOTNULLconstraint:ThisensuresthatacolumndoesnothaveaNULLvalue.TheDEFAULTconstraint:Thisprovidesadefaultvalueforacolumnwhennoneisspecified.TheUNIQUEconstraint:Thisensuresthatallthevaluesinacolumnaredifferent.ThePRIMARYkey:Thisuniquelyidentifiesallrows/recordsinadatabasetable.TheCHECKconstraint:TheCHECKconstraintensuresthatallthevaluesinacolumnsatisfycertainconditions.TheAUTOINCREMENTkeyword:AUTOINCREMENTisakeywordusedtoautoincrementavalueofafieldinthetable.WecanautoincrementafieldvaluebyusingtheAUTOINCREMENTkeywordwhencreatingatablewithaspecificcolumnnametoautoincrementit.ThekeywordAUTOINCREMENTcanbeusedwiththeINTEGERfieldonly.
Thenextstepistoprepareourdatamodel;wewilluseourschematoframethedatamodelclass.TheContactModelclasswillhaveContact_ID,Name,Number,Email,andPhotoasfields,theyarerepresentedasid,name,contactNo,email,andbyteArrayrespectively.Theclasswillconsistofagetter/settermethodtosetandfetchpropertyvaluesasneeded.Theuseofadatamodelwillfacilitateinthecommunicationoftheactivityusedtoshow/processdataandourdatabasehandler,whichwearegoingtodefinelaterinthischapter.WewillcreateanewpackageandanewclassinitcalledtheContactModelclass.Pleasenotethatcreatinganewpackageisnotanecessarystep;itisusedtoorganizeourclassesinalogicalandeasilyaccessiblemanner.Thisclasscanbedescribedasfollows:
publicclassContactModel{
privateintid;
privateStringname,contactNo,email;
privatebyte[]byteArray;
publicbyte[]getPhoto(){
returnbyteArray;
}
publicvoidsetPhoto(byte[]array){
byteArray=array;
}
publicintgetId(){
returnid;
}
publicvoidsetId(intid){
this.id=id;
}
……………
}
TipEclipseprovidesalotofhelpfulshortcutsbutnotforgeneratinggetterandsettermethods.Wecanbindgeneratinggetterandsettermethodstoanykeybindingasperourliking.InEclipse,gotoWindow|Preferences|General|Keys,searchforgetter,andaddyourbindings.WeareusingAlt+Shift+G;youarefreetosetanyotherkeycombination.
AdatabasehandlerandqueriesWewillbuildoursupportclassthatwillcontainmethodstoread,update,anddeletedataasperourdatabaserequirements.Thisclasswillenableustocreateandupdatethedatabaseandwillactasourhubfordatamanagement.WewillusethisclasstorunSQLitequeriesandsendacrossdatatotheUI;inourcase,alistviewtodisplaytheresults:
publicclassDatabaseManager{
privateSQLiteDatabasedb;
privatestaticfinalStringDB_NAME="contact";
privatestaticfinalintDB_VERSION=1;
privatestaticfinalStringTABLE_NAME="contact_table";
privatestaticfinalStringTABLE_ROW_ID="_id";
privatestaticfinalStringTABLE_ROW_NAME="contact_name";
privatestaticfinalStringTABLE_ROW_PHONENUM="contact_number";
privatestaticfinalStringTABLE_ROW_EMAIL="contact_email";
privatestaticfinalStringTABLE_ROW_PHOTOID="photo_id";
.........
}
WewillcreateanobjectoftheSQLiteDatabaseclass,whichwewillinitializelaterwitheithergetWritableDatabase()orgetReadableDatabase().Wewilldefinetheconstantsthatwewillbeusingthroughtheclass.
NoteByconvention,constantsaredefinedincapitalsbutuseofstaticfinalindefiningaconstantisbitmorethantheconvention.Toknowmore,refertohttp://goo.gl/t0PoQj.
Wewilldefinethenameofourdatabaseascontactanddefinetheversionas1.Ifwelookbacktothepreviouschapter,wewillrecalltheimportanceofthisvalue.Aquickrecapofthisenablesustoupgradethedatabasefromthecurrentversiontothenewversion.Theusecasewillbecomeclearwiththisexample.Let’ssayinfuturethereisanewrequirement,thatis,weneedtoaddafaxnumbertoourcontactdetails.Wewillmodifyourcurrentschematoincorporatethischangeandourcontactdatabasewillcorrespondinglychange.Ifweareinstallingtheapplicationonnewdevices,therewillbenoissue;butincaseofadevicewherewealreadyhavearunninginstanceoftheapplication,wewillfaceproblems.Inthissituation,DB_VERSIONwillcomeinhandyandhelpusreplacetheoldversionofthedatabasewiththecurrentversion.Anotherapproachwouldbetouninstalltheapplicationandinstallitagain,butthatisnotencouraged.
Thetablenameandimportantfieldssuchastablecolumnswillbedefinednow.TABLE_ROW_IDisaveryimportantcolumn.Thiswillserveastheprimarykeyforthetable;itwillalsoautoincrementandcannotbenull.NOTNULLisagainacolumnconstraint,whichmayonlybeattachedtoacolumndefinitionandisnotspecifiedasatableconstraint.Notsurprisingly,aNOTNULLconstraintdictatesthattheassociatedcolumnmaynotcontainaNULLvalue.AttemptingtosetthecolumnvaluetoNULLwheninsertinganewroworupdatinganexistingone,causesaconstraintviolation.Thiswillbeusedtofinda
particularvalueinthetable.TheuniquenessoftheIDguaranteesthatwedonothaveanyconflictswithdatainthetable,sinceeachrowisuniquelyidentifiedbythekey.Therestofthetablecolumnsareprettyself-explanatory.TheconstructorfortheDatabaseManagerclassisasfollows:
publicDatabaseManager(Contextcontext){
this.context=context;
CustomSQLiteOpenHelperhelper=newCustomSQLiteOpenHelper(context);
this.db=helper.getWritableDatabase();
}
NoticethatweareusingaclasscalledCustomSQLiteOpenHelper.Wewillcomebacktothislater.WewillusetheclassobjecttogetourSQLitedatabaseinstance.
BuildingtheCreatequeryTocreateatablewiththedesiredcolumns,wewillbuildaquerystatementandexecuteit.Thestatementwillcontainthetablename,differenttablecolumns,andrespectivedatatype.Wewillnowlookatmethodsforcreatinganewdatabaseandalsoupgradinganexistingdatabaseaccordingtotheneedsoftheapplication:
privateclassCustomSQLiteOpenHelperextendsSQLiteOpenHelper{
publicCustomSQLiteOpenHelper(Contextcontext){
super(context,DB_NAME,null,DB_VERSION);
}
@Override
publicvoidonCreate(SQLiteDatabasedb){
StringnewTableQueryString="createtable"
+TABLE_NAME+"("
+TABLE_ROW_ID
+"integerprimarykeyautoincrementnotnull,"
+TABLE_ROW_NAME
+"textnotnull,"
+TABLE_ROW_PHONENUM
+"textnotnull,"
+TABLE_ROW_EMAIL
+"textnotnull,"
+TABLE_ROW_PHOTOID
+"BLOB"+");";
db.execSQL(newTableQueryString);
}
@Override
publicvoidonUpgrade(SQLiteDatabasedb,intoldVersion,
intnewVersion){
StringDROP_TABLE="DROPTABLEIFEXISTS"+
TABLE_NAME;
db.execSQL(DROP_TABLE);
onCreate(db);
}
}
CustomSQLiteOpenHelperextendsSQLiteOpenHelperandprovidesuswiththekeymethodsonCreate()andonUpgrade().WehavedefinedthisclassastheinnerclassofourDatabaseManagerclass.Thisenablesustomanageallthedatabase-relatedfunctions,namelyCRUD(Create,Read,Update,andDelete),fromoneplace.
InourCustomSQLiteOpenHelperconstructor,whichisresponsibleforcreatinganinstanceofourclass,wewillpassacontext,whichinturnwillbepassedtothesuperconstructorwiththefollowingparameters:
Contextcontext:ThisisthecontextwepassedtoourconstructorStringname:ThisisthenameofourdatabaseCursorFactoryfactory:Thisisthecursorfactoryobject,whichcanbepassedasnull
intversion:Thisisthedatabaseversionofthedatabase
ThenextimportantmethodisonCreate().WewillbuildourSQLitequerystring,whichwillcreateourdatabasetable:
"createtable"+TABLE_NAME+"("
+TABLE_ROW_ID
+"integerprimarykeyautoincrementnotnull,"
….....
+TABLE_ROW_PHOTOID+"BLOB"+");";
Thepreviousstatementisbasedonthefollowingsyntaxdiagram:
Here,thekeywordcreatetableisusedtocreateatable.Thisisfollowedbythetablename,thedeclarationofcolumns,andtheirdatatype.AfterpreparingourSQLstatement,wewillexecuteitusingtheexecSQL()methodoftheSQLitedatabase.Incasesomethingiswrongwiththequerystatementthatwebuiltearlier,wewillencountertheexception,android.database.sqlite.SQLiteException.Bydefault,thedatabaseisformedintheinternalmemoryspaceallocatedtotheapplication.Thefoldercanbefoundat/data/data/<yourpackage>/databases/.
Wecaneasilyverifywhetherourdatabaseisformedwhilerunningthispieceofcodeonanemulatororarootedphone.InEclipse,gototheDDMSperspectiveandthengotothefilemanager.Wecaneasilynavigatetothegivenfolderifwehavesufficientpermission,thatis,arooteddevice.Wecanalsopullupourdatabasewiththehelpofthefileexplorer,andwiththehelpofastandaloneSQLitemanagertool,wecanviewourdatabaseandperformCRUDoperationsonitaswell.WhatmakestheAndroidapplication’sdatabasereadablethroughanothertool?Rememberhowwediscussedcross-platforminSQLitefeaturesinthelastchapter?Inthefollowingscreenshot,noticethetablename,theSQLstatementusedtobuildit,andthecolumnnamesalongwiththeirdatatype:
NoteTheSQLiteManagertoolcanbedownloadedeitherintheChromeorFirefoxbrowser.ThefollowingisthelinkforFirefoxextension:http://goo.gl/NLu8JT.
Anotherhandywayofpullingupourdatabaseoranyotherfileisbyusingtheadbpullcommand:
adbpull/data/data/yourpackagename/databases/filelocation
AnotherinterestingpointtonoteisthatthedatatypeofTABLE_ROW_PHOTOIDisBLOB.BLOBstandsforbinarylargeobject.Itisdifferentfromotherdatatype,suchastextandinteger,asitcanstorebinarydata.Thebinarydatacanbeanimage,audio,oranyothertypeofmultimediaobject.
Itisnotadvisabletostorelargeimagesinadatabase;wecanstorefilenamesorlocations,butstoringimagesisbitofoverkill.Imagineasituationlikethiswherewestorecontactimages.Toamplifythissituation,insteadofafewhundredcontacts,makeitafewthousandcontacts.Thesizeofthedatabasewillbecomelargeandtheaccesstimewillalsoincrease.WewanttodemonstratetheuseofBLOBsbystoringcontactimages.
TheonUpgrade()methodiscalledwhenthedatabaseisupgraded.Thedatabaseisupgradedbychangingtheversionnumberofthedatabase.Here,theimplementationdependsontheneedoftheapplication.Insomecases,thewholetablemayhavetobedeletedandanewonemayneedtobecreated,andinsomeapplications,onlyslightmodificationisneeded.HowtomigratefromoneversiontoanotheriscoveredinChapter4,ThreadCarefully.
BuildingtheInsertqueryToinsertanewrowofdatainthedatabasetable,weneedtouseeithertheinsert()methodorwecanmakeaninsertquerystatementandusetheexecute()method:
publicvoidaddRow(ContactModelcontactObj){
ContentValuesvalues=prepareData(contactObj);
try{
db.insert(TABLE_NAME,null,values);
}catch(Exceptione){
Log.e("DBERROR",e.toString());
e.printStackTrace();
}
}
Incaseourtablenameiswrong,SQLitewillgivealognosuchtablemessageandtheexception,android.database.sqlite.SQLiteException.TheaddRow()methodisusedtoinsertcontactdetailsinthedatabaserow;noticethattheparameterofthemethodisanobjectofContactModel.WehavecreatedanadditionalmethodprepareData()toconstructaContentValuesobjectfromtheContactModelobject’sgettermethods:
.......................
values.put(TABLE_ROW_NAME,contactObj.getName());
values.put(TABLE_ROW_PHONENUM,contactObj.getContactNo());
....................
AfterthepreparationoftheContentValuesobject,wearegoingtousetheinsert()methodoftheSQLiteDatabaseclass:
publiclonginsert(Stringtable,StringnullColumnHack,ContentValues
values)
Theparametersoftheinsert()methodareasfollows:
table:Thedatabasetabletoinserttherowinto.values:Thiskey-valuemapcontainstheinitialcolumnvaluesforthetablerow.Columnnamesactaskeys.Valuesasthecolumnvalues.nullColumnHack:Thisisasinterestingasitsname.Here’saquotefromtheAndroiddocumentationwebsite:
“optional;maybenull.SQLdoesn’tallowinsertingacompletelyemptyrowwithoutnamingatleastonecolumnname.Ifyourprovidedvaluesareempty,nocolumnnamesareknownandanemptyrowcan’tbeinserted.Ifnotsettonull,thenullColumnHackparameterprovidesthenameofnullablecolumnnametoexplicitlyinsertNULLintothecasewhereyourvaluesareempty.”
Inshort,incaseswherewearetryingtopassanemptyContentValuestobeinserted,SQLiteneedssomecolumnthatissafetobeassignedNULL.
Alternatively,insteadoftheinsert()method,wecanpreparetheSQLstatementandexecuteitasshown:
publicvoidaddRowAlternative(ContactModelcontactObj){
StringinsertStatment="INSERTINTO"+TABLE_NAME
+"("
+TABLE_ROW_NAME+","
+TABLE_ROW_PHONENUM+","
+TABLE_ROW_EMAIL+","
+TABLE_ROW_PHOTOID
+")"
+"VALUES"
+"(?,?,?,?)";
SQLiteStatements=db.compileStatement(insertStatment);
s.bindString(1,contactObj.getName());
s.bindString(2,contactObj.getContactNo());
s.bindString(3,contactObj.getEmail());
if(contactObj.getPhoto()!=null)
{s.bindBlob(4,contactObj.getPhoto());}
s.execute();
}
Wewillbecoveringalternativesforalotofthemethodswementionedhere.Theideaistomakeyoucomfortablewithotherpossiblewaystobuildandexecutequeries.Theexplanationofthealternativepartisleftasanexerciseforyou.ThegetRowAsObject()methodwillreturnthefetchedrowfromthedatabaseintheformofaContactModelobject,asshowninthefollowingcode.ItwillrequirerowIDasaparametertouniquelyidentifywhichrowinthetablewewanttoaccess:
publicContactModelgetRowAsObject(introwID){
ContactModelrowContactObj=newContactModel();
Cursorcursor;
try{
cursor=db.query(TABLE_NAME,newString[]{
TABLE_ROW_ID,TABLE_ROW_NAME,TABLE_ROW_PHONENUM,TABLE_ROW_EMAIL,
TABLE_ROW_PHOTOID},
TABLE_ROW_ID+"="+rowID,null,
null,null,null,null);
cursor.moveToFirst();
if(!cursor.isAfterLast()){
prepareSendObject(rowContactObj,cursor);}
}catch(SQLExceptione){
Log.e("DBERROR",e.toString());
e.printStackTrace();
}
returnrowContactObj;
}
ThismethodwillreturnthefetchedrowfromthedatabaseintheformofaContactModelobject.WeareusingtheSQLiteDatabase()querymethodtofetchtherowfromourcontacttableagainsttheprovidedrowIDparameter.Themethodreturnsacursorovertheresultset:
publicCursorquery(Stringtable,String[]columns,Stringselection,
String[]selectionArgs,StringgroupBy,Stringhaving,StringorderBy,
Stringlimit)
Thefollowingaretheparametersofthepreviouscode:
table:Thisdenotesthedatabasetableagainstwhichthequerywillberun.columns:Thisisalistofthecolumnsthatarereturned;ifwepassnull,itwillreturnallthecolumns.selection:ThisiswherewedefinewhichrowsaretobereturnedandframedasaSQLWHEREclause.Passingnullwillreturnalltherows.selectionArgs:Wecanpassnullforthisparameterorwemayincludequestionmarksintheselection,whichwillbereplacedbythevaluesfromselectionArgs.groupBy:ThisisafilterframedasaSQLGROUPBYclausedeclaringhowtogrouprows.Passingnullwillcausetherowstonotbegrouped.Having:Thisisafilterthattellswhichrowgroupsaretobemadepartofthecursor,framedasaSQLHAVINGclause.Passingnullwillcausealltherowgroupstobeincluded.OrderBy:ThistellsthequeryhowtoordertherowsframedasanSQLORDERBYclause.Passingnullwillusethedefaultsortorder.limit:ThiswilllimitthenumberofrowsreturnedbythequeryframedastheLIMITclause.PassingnulldenotesanoLIMITclause.
Anotherimportantconcepthereismovingthecursoraroundtoaccessdata.Noticethefollowingmethods:cursor.moveToFirst(),cursor.isAfterLast(),andcursor.moveToNext().
Whenwetrytoretrievedata-buildingSQLquerystatements,thedatabasewillfirstcreateanobjectofthecursorobjectandreturnitsreference.Thepointerofthisreturnedreferenceispointingtothe0thlocation,whichisalsoknownas“beforefirstlocation”ofthecursor.Whenwewanttoretrievedata,wehavetofirstmovetothefirstrecord;hence,theuseofcursor.moveToFirst().Talkingabouttherestofthetwomethods,cursor.isAfterLast()returnswhetherthecursorispointingtothepositionafterthelastrowandcursor.moveToNext()movesthecursortothenextrow.
TipReadersareadvisedtogothroughmoreofthecursormethodsattheAndroiddevelopersite:http://goo.gl/fR75t8.
Alternatively,wecanusethefollowingmethod:
publicContactModelgetRowAsObjectAlternative(introwID){
ContactModelrowContactObj=newContactModel();
Cursorcursor;
try{
StringqueryStatement="SELECT*FROM"
+TABLE_NAME+"WHERE"+TABLE_ROW_ID+"=?";
cursor=db.rawQuery(queryStatement,
newString[]{String.valueOf(rowID)});
cursor.moveToFirst();
rowContactObj=newContactModel();
rowContactObj.setId(cursor.getInt(0));
prepareSendObject(rowContactObj,cursor);
}catch(SQLExceptione){
Log.e("DBERROR",e.toString());
e.printStackTrace();
}
returnrowContactObj;
}
Theupdatestatementisbasedonthefollowingsyntaxdiagram:
Beforewemovetoothermethodsinthedatamanagerclass,let’shavealookatfetchingdatafromacursorobjectintheprepareSendObject()method:
rowObj.setContactNo(cursor.getString(cursor.getColumnIndexOrThrow(TABLE_ROW
_PHONENUM)));
rowObj.setEmail(cursor.getString(cursor.getColumnIndexOrThrow(TABLE_ROW_EMA
IL)));
Herecursor.getstring()takesthecolumnindexasaparameterandreturnsthevalueoftherequestedcolumn,whereascursor.getColumnIndexOrThrow()takesthecolumnnameasaparameterandreturnsthezero-basedindexforthegivencolumnname.Instead
ofthischainingapproach,wecandirectlyusecursor.getstring().Ifweknowthecolumnnumberoftherequiredcolumntofetchdatafrom,wecanusethefollowingnotation:
cursor.getstring(2);
BuildingtheDeletequeryTodeleteaparticularrowofdatafromourdatabasetable,weneedtoprovidetheprimarykeytouniquelyidentifythedatasettoberemoved:
publicvoiddeleteRow(introwID){
try{
db.delete(TABLE_NAME,TABLE_ROW_ID
+"="+rowID,null);
}catch(Exceptione){
Log.e("DBERROR",e.toString());
e.printStackTrace();
}
}
ThismethodusestheSQLiteDatabasedelete()methodtodeletetherowofthegivenIDinthetable:
publicintdelete(Stringtable,StringwhereClause,String[]whereArgs)
Thefollowingaretheparametersoftheprecedingcodesnippet:
table:ThisisthedatabasetableagainstwhichthequerywillberunwhereClause:Thisisaclausetobeappliedwhendeletingarow;passingnullinthisclausewilldeletealltherowswhereArgs:Wemayincludequestionmarksinthewhereclause,whichwillbereplacedbythevaluesthatwillbeboundasstrings
Alternatively,wecanusethefollowingmethod:
publicvoiddeleteRowAlternative(introwId){
StringdeleteStatement="DELETEFROM"
+TABLE_NAME+"WHERE"
+TABLE_ROW_ID+"=?";
SQLiteStatements=db.compileStatement(deleteStatement);
s.bindLong(1,rowId);
s.executeUpdateDelete();
}
Thedeletestatementisbasedonthefollowingsyntaxdiagram:
BuildingtheUpdatequeryToupdateanexistingvalue,weneedtousetheupdate()methodwiththerequiredparameters:
publicvoidupdateRow(introwId,ContactModelcontactObj){
ContentValuesvalues=prepareData(contactObj);
StringwhereClause=TABLE_ROW_ID+"=?";
StringwhereArgs[]=newString[]{String.valueOf(rowId)};
db.update(TABLE_NAME,values,whereClause,whereArgs);
}
Generally,weneedtheprimarykey,inourcasetherowIdparameter,toidentifytherowtobemodified.AnSQLiteDatabaseupdate()methodisusedtomodifytheexistingdataofzeroormorerowsinadatabasetable:
publicintupdate(Stringtable,ContentValuesvalues,StringwhereClause,
String[]whereArgs)
Thefollowingaretheparametersoftheprecedingcodesnippet:
table:Thisisthequalifieddatabasetablenametobeupdated.values:Thisisamappingfromthecolumnnamestothenewcolumnvalues.whereClause:ThisistheoptionalWHEREclausetobeappliedwhenupdatingavalue/row.IftheUPDATEstatementdoesnothaveaWHEREclause,alltherowsinthetablearemodified.whereArgs:Wemayincludequestionmarksinthewhereclause,whichwillbereplacedbythevaluesthatwillbeboundasstrings.
Alternatively,youcanusethefollowingcode:
publicvoidupdateRowAlternative(introwId,ContactModelcontactObj){
StringupdateStatement="UPDATE"+TABLE_NAME+"SET"
+TABLE_ROW_NAME+"=?,"
+TABLE_ROW_PHONENUM+"=?,"
+TABLE_ROW_EMAIL+"=?,"
+TABLE_ROW_PHOTOID+"=?"
+"WHERE"+TABLE_ROW_ID+"=?";
SQLiteStatements=db.compileStatement(updateStatement);
s.bindString(1,contactObj.getName());
s.bindString(2,contactObj.getContactNo());
s.bindString(3,contactObj.getEmail());
if(contactObj.getPhoto()!=null)
{s.bindBlob(4,contactObj.getPhoto());}
s.bindLong(5,rowId);
s.executeUpdateDelete();
}
Theupdatestatementisbasedonthefollowingsyntaxdiagram:
ConnectingtheUIanddatabaseNowthatwehaveourdatabasehooksinplace,let’sconnectourUIwiththedata:
1. Thefirststepwouldbetogetthedatafromtheuser.WecanusetheexistingcontactdatafromtheAndroid’scontactapplicationbymeansofthecontentprovider.
Wewillbecoveringthisapproachinthenextchapter.Fornow,wewillbeaskingtheusertoaddanewcontact,whichwewillinsertintothedatabase:
2. WeareusingstandardAndroidUIwidgets,suchasEditText,TextView,andButtonstocollectthedataprovidedbytheuser:
privatevoidprepareSendData(){
if(TextUtils.isEmpty(contactName.getText().toString())
||TextUtils.isEmpty(
contactPhone.getText().toString())){
.............
}else{
ContactModelcontact=newContactModel();
contact.setName(contactName.getText().toString());
............
DatabaseManagerdm=newDatabaseManager(this);
if(reqType==ContactsMainActivity
.CONTACT_UPDATE_REQ_CODE){
dm.updateRowAlternative(rowId,contact);
}else{
dm.addRowAlternative(contact);
}
setResult(RESULT_OK);
finish();
}
}
prepareSendData()isthemethodthatisresponsibleforbundlingdataintoourobjectmodelandlaterinsertingitinourdatabase.NoticethatinsteadofusingnullcheckandlengthcheckoncontactName,weareusingTextUtils.isEmpty(),whichisaveryhandymethod.Thisreturnstrueifthestringisnullorofzerolength.
3. WeprepareourContactModelobjectfromthedatareceivedbytheuserfillingtheform.WecreateaninstanceofourDatabaseManagerclassandaccessouraddRow()methodpassingourcontactobjecttobeinsertedinthedatabase,aswediscussedearlier.
AnotherimportantmethodisgetBlob(),whichisusedtogettheimagedataintheBLOBformat:
privatebyte[]getBlob(){
ByteArrayOutputStreamblob=newByteArrayOutputStream();
imageBitmap.compress(Bitmap.CompressFormat.JPEG,100,blob);
byte[]byteArray=blob.toByteArray();
returnbyteArray;
}
4. WecreateanewByteArrayOutputStreamobjectblob.Bitmap’scompress()methodwillbeusedtowriteacompressedversionofthebitmaptoouroutputstreamobject:
publicbooleancompress(Bitmap.CompressFormatformat,intquality,
OutputStreamstream)
Thefollowingaretheparametersoftheprecedingcode:
format:Thisistheformatofacompressedimage,inourcase,JPEG.quality:Thisisahinttothecompressor,whichrangesfrom0to100.Thevalue0meanstocompresstoasmallersizeandlowquality,while100isfor
maximumquality.stream:Thisistheoutputstreamtowritethecompresseddatato.
5. Then,wecreateourbyte[]object,whichwillbeconstructedfromtheByteArrayOutputStreamtoByteArray()method.
NoteYouwillnoticethatwearenotcoveringallthemethods;onlythosethatarerelevanttodataoperationsandsomemethodsorcallsthatmightcauseconfusion.Thereareafewmoremethodsthatareusedtoinvokethecameraorgallerytopickaphototobeusedasthecontactimage.Youareadvisedtoexplorethemethodsinthecodeprovidedalongwiththebook.
Let’smoveontothepresentationpartwhereweuseacustomlistviewtodisplayourcontactinformationinapresentableandreadablemanner.Wearegoingtoskipabulkofthecoderelatedtothepresentationandconcentrateonthepartswherewefetchandprovidedatatoourlistview.Wewillalsoimplementacontextmenuinordertoprovideauserwiththefunctionalityofdeletingaparticularcontact.WewillbetouchingbaseonthedatabasemanagermethodssuchasgetAllData()tofetchallouraddedcontacts.WewillusedeleteRow()inordertoremoveanyunwantedcontactsfromourcontactsdatabase.Thefinaloutcomewillbesomethinglikethefollowingscreenshot:
6. Tomakeacustomlistviewsimilartotheoneshownintheprecedingscreenshot,wecreateCustomListAdapterextendingBaseAdapterandusingthecustomlayoutforthelistviewrows.NoticeinthefollowingconstructorwehaveinitializedanewarraylistandwilluseourdatabasemanagertofetchvaluesbyusingthegetAllData()methodtofetchallthedatabaseentries:
publicCustomListAdapter(Contextcontext){
contactModelList=newArrayList<ContactModel>();
_context=context;
inflater=(LayoutInflater)context.getSystemService(
Context.LAYOUT_INFLATER_SERVICE);
dm=newDatabaseManager(_context);
contactModelList=dm.getAllData();
}
AnotherveryimportantmethodisthegetView()method.Thisiswhereweinflateourcustomlayoutinaview:
convertView=inflater.inflate(R.layout.contact_list_row,null);
Wewillusetheviewholderpatterntoimprovethelistviewscrollingsmoothness:
vHolder=(ViewHolder)convertView.getTag();
7. Andfinally,setthedatatothecorrespondingviews:
vHolder.contact_email.setText(contactObj.getEmail());
NoteHoldingviewobjectsinaviewholderimprovestheperformancebyreducingcallstofindViewById().Youcanreadmoreaboutthisandhowtomakelistviewscrollingsmoothathttp://developer.android.com/training/improving-layouts/smooth-scrolling.html.
8. Wewillalsobeimplementingawaytodeletealistviewentry.Wewillusethecontextmenuforthispurpose.Wewillfirstcreateamenuiteminthemenufolderunderresofourapplicationstructure:
<?xmlversion="1.0"encoding="utf-8"?>
<menuxmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/delete_item"
android:title="Delete"/>
<item
android:id="@+id/update_item"
android:title="Update"/>
</menu>
9. Now,inourmainactivitywherewewilldisplayourlistview,wewillusethefollowingcalltoregisterourlistviewwiththecontextmenu.Inordertolaunchthecontextmenu,weneedtoperformalongpressactiononthelistviewitem:
registerForContextMenu(listReminder)
10. Thereareafewmoremethodsthatweneedtoimplementinordertoachievethedeletefunctionality:
@Override
publicvoidonCreateContextMenu(ContextMenumenu,Viewv,
ContextMenuInfomenuInfo){
super.onCreateContextMenu(menu,v,menuInfo);
MenuInflaterm=getMenuInflater();
m.inflate(R.menu.del_menu,menu);
}
ThismethodisusedtoinflatethecontextmenuwiththemenuwedefinedearlierinXML.TheMenuInfaterclassgeneratesmenuobjectsfromthemenuXMLfiles.MenuinflationreliesheavilyonthepreprocessingofXMLfilesthatisdoneatbuildtime;thisisdonetoimproveperformance.
11. Now,wewillimplementamethodtocapturetheclickonthecontextmenu:
@Override
publicbooleanonContextItemSelected(MenuItemitem){
..............
caseR.id.delete_item:
cAdapter.delRow(info.position);
cAdapter.notifyDataSetChanged();
returntrue;
caseR.id.update_item:
Intentintent=newIntent(
ContactsMainActivity.this,AddNewContactActivity.class);
......................
}
12. Here,wewillfindthepositionIDoftheclickedlistviewitemandinvokethedelRow()methodoftheCustomListAdapter,andintheend,wewillnotifytheadapterthatthedatasethaschanged:
publicvoiddelRow(intdelPosition){
dm.deleteRowAlternative(contactModelList.get(delPosition).getId());
contactModelList.remove(delPosition);
ThedelRow()methodisresponsibleforconnectingourdatabase’sdeleteRowAlternative()methodtoourcontextmenu’sdelete()method.Here,wefetchtheIDoftheobjectsetontheparticularlistviewitemandpassittothedeleteRowAlternative()methodofdatabaseManagerinordertodeletethedatafromthedatabase.Afterremovingthedatafromthedatabase,wewillinstructourlistviewtoremovethecorrespondingentryfromourcontactlist.
IntheonContextItemSelected()method,wecanalsoseetheupdate_itemincasetheuserhasclickedontheupdatebutton.Wewilllaunchtheactivitytoaddanewcontact
andaddthedatawealreadyhaveincasetheuserwantstoeditsomefields.Thecatchistoknowfromwherethecallhasbeeninitiated.Isittoaddanewentryorupdateanexistingone?Wetakethehelpofthefollowingcodetotelltheactivitythatthisactionisusedtoupdateratherthanaddanewentry:
intent.putExtra(REQ_TYPE,CONTACT_UPDATE_REQ_CODE);
SummaryInthischapter,wecoveredthestepsofbuildingupadatabase-basedapplication,fromscratchandthenfromschematoobjectmodelandthenfromobjectmodeltobuildingactualdatabases.WeunderwenttheprocessofbuildingourdatabasemanagerandfinallyimplementedtheUIdatabaseconnecttoachieveafullyfunctionalapplication.Thetopicscoveredrangedfromthebuildingblocksofthemodelclass,databaseschematoourdatabasehandler,andCRUDmethods.WealsocoveredtheimportantconceptofconnectingadatabasetotheAndroidviewswithproperhooksinplacetopickupuserdata,adddatatothedatabase,andshowrelevantinformationafterpickingupdatafromthedatabase.
Inthenextchapter,wewillfocusonbuildinguponthegroundworkwehavedonehere.WewillexploreContentProviders.WewillalsolearnhowtofetchdatafromContentProviders,howtomakeourowncontentprovider,thebestpracticesassociatedwhilebuildingthem,andmuchmore.
Chapter3.SharingisCaring “Datareallypowerseverythingthatwedo.”
—–JeffWeiner,LinkedIn
Inthelastchapter,westartedprogrammingourveryowncontactmanager.Wecameacrossvariousbuildingblocksofadatabase-centricapplication;wecovereddatabasehandlersandbuildingqueriesinordertogetmeaningfuldatafromourdatabase.WealsoexploredhowtomakeaconnectionbetweenourUIanddatabaseandpresentitinaconsumablemannerfortheenduser.
Inthischapter,wewilllearnhowtoaccessotherapplication’sdataviameansofcontentproviders.Wewillalsolearnhowtobuildourveryowncontentproviderinordertoshareourdatawithotherapplications.WewilllookintoAndroid’sproviderssuchascontactprovider.Towrapthingsup,wewillconstructatestapplicationtouseournewlyconstructedcontentprovider.
Inthischapter,wewillcoverthefollowingtopics:
Whatisacontentprovider?CreatingacontentproviderImplementingthecoremethodsUsingacontentprovider
Whatisacontentprovider?AcontentprovideristhefourthcomponentofanAndroidapplication.Itisusedtomanageaccesstoastructuredsetofdata.Contentprovidersencapsulatethedata,andprovideabstractionandthemechanismtodefinedatasecurity.However,contentprovidersareprimarilyintendedtobeusedbyotherapplicationsthataccesstheproviderusingaprovider’sclientobject.Together,providersandproviderclientsofferaconsistent,standardinterfacefordata,whichalsohandlesinterprocesscommunicationandsecuredataaccess.
Acontentproviderallowsoneapptosharedatawithotherapplications.Bydesign,anAndroidSQLitedatabasecreatedbyanapplicationisprivatetotheapplication;itisexcellentifyouconsiderthesecuritypointofview,buttroublesomewhenyouwanttosharedataacrossdifferentapplications.Thisiswhereacontentprovidercomestotherescue;youcaneasilysharedatabybuildingyourcontentprovider.Itisimportanttonotethatalthoughourdiscussionwillfocusonadatabase,acontentproviderisnotlimitedtoit.Itcanalsobeusedtoservefiledatathatnormallygoesintofiles,suchasphotos,audio,orvideos:
Intheprecedingdiagram,noticehowtheinteractionbetweenApplicationsAandBhappenswhileexchangingdata.Here,wehaveanApplicationAwhoseactivityneedstoaccessthedatabaseofApplicationB.Aswehavealreadyseen,thedatabaseofApplicationBisstoredintheinternalmemoryandcannotbedirectlyaccessedbyApplicationA.ThisiswhereContentProvidercomesintothepicture;itallowsustosharedataandmodifyaccesstootherapplications.Thecontentproviderimplementsmethodstoquery,insert,update,anddeletedataindatabases.ApplicationAnowrequeststhecontentprovidertoperformsomedesiredoperationsonbehalfofit.Wewillexplorebothsidesofthecoin,butwewillfirstuseContentProvidertofetchcontactsfromaphone’scontactdatabase,andthenwewillbuildourveryowncontentproviderforothers
topickdatafromourdatabase.
UsingexistingcontentprovidersAndroidlistsalotofstandardcontentprovidersthatwecanuse.SomeofthemareBrowser,CalendarContract,CallLog,Contacts,ContactsContract,MediaStore,userDictionary,andsoon.
Inourcurrentcontactmanagerapplication,wewilladdanewfeature.IntheUIoftheAddNewContactActivityclass,wewilladdasmallbuttontofetchcontactsfromaphone’scontactlistwithhelpfromthesystem’sexistingContentProviderandContentResolverproviders.WewillbeusingtheContactsContractproviderforthispurpose.
Whatisacontentresolver?TheContentResolverobjectintheapplication’scontextisusedtocommunicatewiththeproviderasaclient.TheContentResolverobjectcommunicateswiththeproviderobject—aninstanceofaclassthatimplementsContentProvider.Theproviderobjectreceivesdatarequestsfromclients,performstherequestedaction,andreturnstheresults.
ContentResolverisasingle,globalinstanceinourapplicationthatprovidesaccesstootherapplication’scontentproviders;wedonotneedtoworryabouthandlinginterprocesscommunication.TheContentResolvermethodsprovidethebasicCRUD(create,retrieve,update,anddelete)functionsofpersistentstorage;ithasmethodsthatcallidenticallynamedmethodsintheproviderobjectbutdoesnotknowtheimplementation.WewillcoverContentResolverinmoredetailasweprogressthroughthischapter.
Intheprecedingscreenshot,noticethenewiconontheright-handsidetoaddcontactsdirectlyfromthephonecontacts;wemodifiedtheexistingXMLtoaddtheicon.ThecorrespondingclassAddNewContactActivitywillalsobemodified:
publicvoidpickContact(){
try{
IntentcIntent=newIntent(Intent.ACTION_PICK,
ContactsContract.Contacts.CONTENT_URI);
startActivityForResult(cIntent,PICK_CONTACT);
}catch(Exceptione){
e.printStackTrace();
Log.i(TAG,"Exceptionwhilepickingcontact");
}
}
WeaddedanewmethodpickContact()toprepareanintentinordertopickcontacts.Intent.ACTION_PICKallowsustopickanitemfromadatasource;inaddition,allweneedtoknowistheUniformResourceIdentifier(URI)oftheprovider,whichinourcaseisContactsContract.Contacts.CONTENT_URI.ThisfunctionalityisalsoprovidedbyMessaging,Gallery,andContacts.IfyoulookintothecodefromChapter2,ConnectingtheDots,youwillfindwehaveusedthesamecodetopickimagesfromGallery.TheContactsscreenwillpopupallowingustobrowseorsearchforcontactswerequiretomigratetoournewapplication.NoticeonActivityResult,thatis,ournextstopwewillmodifythismethodtohandleourcorrespondingrequesttohandlecontacts.LetuslookatthecodewehavetoaddtopickcontactsfromanAndroid’scontactprovider:
{
.
.
.
elseif(requestCode==PICK_CONTACT){
if(resultCode==Activity.RESULT_OK)
{
UricontactData=data.getData();
Cursorc=getContentResolver().query(contactData,null,null,
null,null);
if(c.moveToFirst()){
Stringid=c
.getString(c
.getColumnIndexOrThrow(ContactsContract.Contacts._ID));
StringhasPhone=c
.getString(c
.getColumnIndex(ContactsContract.Contacts.HAS_PHONE_NUMBER));
if(hasPhone.equalsIgnoreCase("1")){
Cursorphones=getContentResolver()
.query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
null,
ContactsContract.CommonDataKinds.Phone.CONTACT_ID
+"="+id,null,null);
phones.moveToFirst();
contactPhone.setText(phones.getString(phones
.getColumnIndex("data1")));
contactName
.setText(phones.getString(phones
.getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME)));
}
…..
TipToaddalittleflairtoyourapplication,downloadtheentiresetofstencils,sources,theactionbariconpack,colorswatches,andtheRobotofontfamilyfromtheAndroiddevelopersite,http://goo.gl/4Msuct.DesigningafunctionalapplicationisincompletewithoutaconsistentUIthatfollowsAndroidguidelines.
Westartbycheckingwhethertherequestcodematchesours.Then,wecross-checkresultcode.WegettheContentResolverobjectbymakingacalltogetcontentresolverontheContextobject;itisamethodoftheandroid.content.Contextclass.AsweareinanactivitythatinheritsfromContext,wedonotneedtobeexplicitinmakingacalltoit.Thesamegoesforservices.Wewillnowverifywhetherthecontactwepickedhasaphonenumberornot.Afterverifyingthenecessarydetails,wepullthedatathatwerequire,suchascontactnameandphonenumber,andsettheminrelevantfields.
CreatingacontentproviderAcontentproviderprovidesaccesstodataintwoways:oneisstructureddatathatgoesintheformofadatabase,astheexampleweareworkingoncurrently,orintheformoffiledata,thatis,datathatgoesintheformofpictures,audio,video,andsoonstoredintheprivatespaceoftheapplication.Beforewebegindiggingintohowtocreateacontentprovider,weshouldalsoretrospectwhetherweneedone.Ifwewanttoofferdatatootherapplications,allowuserstocopydatafromourapptoanother,orusethesearchframeworkinourapplication,thentheanswerisyes.
JustlikeotherAndroidcomponents(Activity,Service,orBroadcastReceiver),acontentprovideriscreatedbyextendingtheContentProviderclass.SinceContentProviderisanabstractclass,wehavetoimplementthesixabstractmethods.Thesemethodsareasfollows:
Method Usage
voidonCreate() Initializestheprovider
StringgetType(Uri)ReturnstheMIMEtypeofdatainthecontentprovider
intdelete(Uriuri,Stringselection,String[]selectionArgs)Deletesdatafromthecontentprovider
Uriinsert(Uriuri,ContentValuesvalues)Insertsnewdataintothecontentprovider
Cursorquery(Uriuri,String[]projection,Stringselection,
String[]selectionArgs,StringsortOrder)Returnsdatatothecaller
intupdate(Uriuri,ContentValuesvalues,Stringselection,String[]
selectionArgs)
Updatestheexistingdatainthecontentprovider
Thesemethodswillbedealtwithinmoredetaillaterasweprogressthroughthechapterandbuildourapplication.
UnderstandingcontentURIsEverydataaccessmethodofContentProviderhasacontentURI,asanargumentthatallowsittodeterminethetable,row,orfiletoaccess.Itgenerallyfollowsthefollowingstructure:
content://authority/Path/Id
Let’sanalyzethebreakdownofthecomponentsofthecontent://URI.Theschemeforcontentprovidersisalwayscontent.Thecolonanddouble-slash(://)actasaseparatorfromtheauthoritypart.Then,wehavetheauthoritypart.Byrule,authoritieshavetobeuniqueforeverycontentprovider.ThenamingconventiontheAndroiddocumentationrecommendsusingisthefullyqualifiedclassnameofyourcontentprovidersubclass.Generally,itisbuiltasapackagenameplusaqualifierforeachcontentproviderwepublish.
Theremainingpartisoptional,alsoreferredtoaspath,andisusedforsegregationbetweendifferenttypesofdataourcontentprovidercanprovide.AverygoodexampleistheMediaStoreproviderwhichneedstodistinguishbetweenaudio,video,andimagefiles.
Anotheroptionalpartisid,whichpointstoaspecificrecord;dependingonwhetheridispresentornot,theURIbecomesID-basedordirectory-based,respectively.AnotherwaytounderstanditwouldbethatanID-basedURIenablesustointeractwithdataindividuallyatrowlevel,whereasadirectory-basedURIenablesustointeractwithmultiplerowsofadatabase.
Forexample,considercontent://com.personalcontactmanager.provider/contacts;wewillencounterthissoonenoughaswemoveaheadwiththechapterwherewedefinehowtoaccessthecontentproviderwearecurrentlybuilding.
NoteOnasidenote,thepackagenameforapplicationsshouldalwaysbeunique;thisisbecausealltheapplicationsonPlayStoreareidentifiedbytheirpackagename.AlltheupdatesforanapplicationonPlayStoreneedtohavethesamepackagenameandbesignedwiththesamekeystoreusedinitially.Forinstance,thefollowingisthePlayStorelinkofaGmailapplication;noticethatattheendofURL,wewillfindthepackagenameoftheapplication:
play.google.com/store/apps/details?id=com.google.android.gm
DeclaringourcontractclassDeclaringacontractisaveryimportantpartofbuildingourcontentprovider.Thisclass,asthenamesuggests,willactasacontractbetweenourcontentproviderandtheapplicationthatisgoingtoaccessourcontentprovider.Itisapublicfinalclass,whichcontainsconstantdefinitionsforURIs,columnnames,andothermetadata.ItcanalsocontainJavadoc,butthebiggestadvantageisthatthedeveloperusingitneednotworryaboutthenamesoftables,columns,andconstants,leadingtolesserror-pronecode.
Thecontractclassprovidesuswiththenecessaryabstraction;wecanchangetheunderlyingoperationsasandwhenrequiredandwecanalsochangethecorrespondingdatamanipulationaffectingotherdependentapplications.Animportantthingtonoteisthatweneedtobecarefulwhilechangingthecontractinfuture;ifwearenotcareful,wemightbreaktheotherapplicationsthatareusingourcontractclass.
Ourcontractclasslookslikethefollowing:
publicfinalclassPersonalContactContract{
/**
*TheauthorityofthePersonalContactProvider
*/
publicstaticfinalStringAUTHORITY=
"com.personalcontactmanager.provider";
publicstaticfinalStringBASE_PATH="contacts";
/**
*TheUriforthetop-levelPersonalContactProvider
*authority
*/
publicstaticfinalUriCONTENT_URI=Uri.parse("content://"+AUTHORITY
+"/"+BASE_PATH);
/**
*Themimetypeofadirectoryofitems.
*/
publicstaticfinalStringCONTENT_TYPE=
ContentResolver.CURSOR_DIR_BASE_TYPE+
"/vnd.com.personalcontactmanager.provider.table";
/**
*Themimetypeofasingleitem.
*/
publicstaticfinalStringCONTENT_ITEM_TYPE=
ContentResolver.CURSOR_ITEM_BASE_TYPE+
"/vnd.com.personalcontactmanager.provider.table_item";
/**
*Aprojectionofallcolumns
*intheitemstable.
*/
publicstaticfinalString[]PROJECTION_ALL={"_id",
"contact_name","contact_number",
"contact_email","photo_id"};
/**
*Thedefaultsortorderfor
*queriescontainingNAMEfields.
*/
//publicstaticfinalStringSORT_ORDER_DEFAULT=NAME+"ASC";
publicstaticfinalclassColumns{
publicstaticStringTABLE_ROW_ID="_id";
publicstaticStringTABLE_ROW_NAME="contact_name";
publicstaticStringTABLE_ROW_PHONENUM="contact_number";
publicstaticStringTABLE_ROW_EMAIL="contact_email";
publicstaticStringTABLE_ROW_PHOTOID="photo_id";
}
}
AUTHORITYisthesymbolicnamethatidentifiestheprovideramongmanyotherprovidersregisteredaspartofanAndroidsystem.BASE_PATHisthepathofthetable.CONTENT_URIistheURIofthetableencapsulatedbytheprovider.CONTENT_TYPEistheAndroidplatform’sbaseMIMEtypeforcontentURIcontainingacursorofzeroormoreitems.CONTENT_ITEM_TYPEistheAndroidplatform’sbaseMIMEtypeforcontentURIscontainingacursorofasingleitem.PROJECTION_ALLandColumnscontainthecolumnIDsofthetable.
Withoutthisinformation,otherdeveloperswillnotbeabletoaccessyourprovidereventhoughitisopenforaccess.
NoteTherecanbemanytablesinsideaproviderandeachshouldhaveauniquepath;thepathisnotarealphysicalpathbutanidentifier.
CreatingUriMatcherdefinitionsUriMatcherisautilityclass,whichaidsinmatchingURIsincontentproviders.TheaddURI()methodtakesthecontentURIpatternsthattheprovidershouldrecognize.WeaddaURItomatch,andthecodetoreturnwhenthisURIismatched:
addURI(Stringauthority,Stringpath,intcode)
Wepassauthority,apathpattern,andanintegervaluetotheaddURI()methodofUriMatcher;itreturnstheintvalue,whichwedefinedasconstantwhenwetriedtomatchpatterns.
OurUriMatcherlookslikethefollowing:
privatestaticfinalintCONTACTS_TABLE=1;
privatestaticfinalintCONTACTS_TABLE_ITEM=2;
privatestaticfinalUriMatchermmURIMatcher=new
UriMatcher(UriMatcher.NO_MATCH);
static{
mmURIMatcher.addURI(PersonalContactContract.AUTHORITY,
PersonalContactContract.BASE_PATH,CONTACTS_TABLE);
mmURIMatcher.addURI(PersonalContactContract.AUTHORITY,
PersonalContactContract.BASE_PATH+"/#",
CONTACTS_TABLE_ITEM);
}
Noticethatitalsosupportstheuseofwildcards;wehaveusedhashtag(#)intheprecedingcodesnippet,wecanalsousewildcardssuchas*.Inourcase,withthehashtag,"content://com.personalcontactmanager.provider/contacts/2"thisexpressionmatches,butusing*"content://com.personalcontactmanager.provider/contactsitdoesn’t.
ImplementingthecoremethodsInordertobuildourcontentprovider,thenextstepwillbetoprepareourcoredatabaseaccessanddatamodifyingmethods,betterknownasCRUDmethods.Thisiswherethecorelogicofhowwewanttointeractwithourdatadependingontheinsert,query,ordeletecallsreceivedisspecified.WewillalsoimplementtheAndroidarchitecture’slifecyclemethodssuchasonCreate().
InitializingtheproviderthroughtheonCreate()methodWecreateanobjectofourdatabasemanagerclassinonCreate().Thereshouldbeminimumoperationsinoncreate()asitrunsontheMainUIthread,anditmaycauselagforsomeusers.Itisgoodpracticetoavoidlong-runningtasksinoncreate()asitincreasesthestartuptimeoftheprovider.Itisevenrecommendedtodeferdatabasecreationanddataloadinguntilourprovideractuallyreceivesarequestforthedata,thatis,tomovelong-lastingactionstotheCRUDmethods:
@Override
PublicBooleanonCreate(){
dbm=newDatabaseManager(getContext());
returnfalse;
}
Queryingrecordsthroughthequery()methodThequery()methodwillreturnacursorovertheresultset.TheURIispassedtoourUriMatchertoseewhetheritmatchesanypatternswedefinedearlier.Inourswitchcasestatement,ifitisatable-item-relatedcase,wecheckwhethertheselectionstatementisempty;incaseitis,webuildourselectionstatementuptothelastpathsegment,elseweappendtheselectiontothelastpathsegmentstatement.WeuseaDatabaseManagerobjecttoarunqueryonthedatabaseandgetacursorasaresult.Itisexpectedofthequery()methodtothrowanIllegalArgumentExceptiontoinformofanunknownURI;itisalsogoodpracticetothrowanullPointerExceptionincaseweencounteraninternalerrorduringthequeryprocess:
@Override
publicCursorquery(Uriuri,String[]projection,Stringselection,
String[]selectionArgs,StringsortOrder){
inturiType=mmURIMatcher.match(uri);
switch(uriType){
caseCONTACTS_TABLE:
break;
caseCONTACTS_TABLE_ITEM:
if(TextUtils.isEmpty(selection)){
selection=PersonalContactContract.Columns.TABLE_ROW_ID
+"="+uri.getLastPathSegment();
}else{
selection=PersonalContactContract.Columns.TABLE_ROW_ID
+"="+uri.getLastPathSegment()+
"and"+selection;
}
break;
default:
thrownewIllegalArgumentException("UnknownURI:"+uri);
}
Cursorcr=dbm.getRowAsCursor(projection,selection,
selectionArgs,sortOrder);
returncr;
}
NoteRememberthatanAndroidsystemmustbeabletocommunicatetheexceptionacrossprocessboundaries.Androidcandothisforthefollowingexceptionsthatmaybeusefulinhandlingqueryerrors:
IllegalArgumentException:YoumaychoosetothrowthisifyourproviderreceivesaninvalidcontentURINullPointerException:Thisisthrownwhentheobjectisnullandwetrytoaccessitsfieldormethod
Addingrecordsthroughtheinsert()methodAsthenamesuggests,theinsert()methodisusedtoinsertavalueinourdatabase.ItreturnstheURIoftheinsertedrowand,whilecheckingtheURI,weneedtorememberthataninsertioncanhappenatthetablelevel,hencetheoperationsinthemethodareprocessedattheURIthatmatchesthetable.Aftermatching,weusethestandardDatabaseManagerobjecttoinsertournewvalueintothedatabase.ThecontentURIforthenewrowisconstructedbyappendingthenewrow’s_IDvaluetothetable’scontentURI:
@Override
publicUriinsert(Uriuri,ContentValuesvalues){
inturiType=mmURIMatcher.match(uri);
longid;
switch(uriType){
caseCONTACTS_TABLE:
id=dbm.addRow(values);
break;
default:
thrownewIllegalArgumentException("UnknownURI:"+uri);
}
Uriur=ContentUris.withAppendedId(uri,id);
returnur;
}
Updatingrecordsthroughtheupdate()methodTheupdate()methodupdatesanexistingrowintheappropriatetable,usingthevaluesintheContentValuesargument.First,weidentifytheURI,whetheritisdirectory-basedorID-based,thenwebuildourselectionstatementaswedidinthequery()method.Now,wewillexecutethestandardupdateRow()methodofDatabaseManagerthatwedefinedearlierwhilebuildingthisapplicationinChapter2,ConnectingtheDots,whichreturnsthenumberofaffectedrows.
Theupdate()methodreturnsthenumberofrowsupdated.Basedontheselectionclause,oneormorerowscanbeupdated:
@Override
publicintupdate(Uriuri,ContentValuesvalues,Stringselection,
String[]selectionArgs){
inturiType=mmURIMatcher.match(uri);
switch(uriType){
caseCONTACTS_TABLE:
break;
caseCONTACTS_TABLE_ITEM:
if(TextUtils.isEmpty(selection)){
selection=PersonalContactContract.Columns.TABLE_ROW_ID
+"="+uri.getLastPathSegment();
}else{
selection=PersonalContactContract.Columns.TABLE_ROW_ID
+"="+uri.getLastPathSegment()
+"and"+selection;
}
break;
default:
thrownewIllegalArgumentException("UnknownURI:"+uri);
}
intcount=dbm.updateRow(values,selection,selectionArgs);
returncount;
}
Deletingrecordsthroughthedelete()methodThedelete()methodisverysimilartotheupdate()methodandtheprocessofusingitissimilar;here,thecallismadetodeletearowinsteadofupdatingit.Thedelete()methodreturnsthenumberofrowsdeleted.Basedontheselectionclause,oneormorerowscanbedeleted:
@Override
publicintdelete(Uriuri,Stringselection,String[]selectionArgs){
inturiType=mmURIMatcher.match(uri);
switch(uriType){
caseCONTACTS_TABLE:
break;
caseCONTACTS_TABLE_ITEM:
if(TextUtils.isEmpty(selection)){
selection=PersonalContactContract.Columns.TABLE_ROW_ID
+"="+uri.getLastPathSegment();
}else{
selection=PersonalContactContract.Columns.TABLE_ROW_ID
+"="+uri.getLastPathSegment()
+"and"+selection;
}
break;
default:
thrownewIllegalArgumentException("UnknownURI:"+uri);
}
intcount=dbm.deleteRow(selection,selectionArgs);
returncount;
}
GettingthereturntypeofdatathroughthegetType()methodThesignatureofthissimplemethodtakesaURIandreturnsastringvalue;everycontentprovidermustreturnthecontenttypeforitssupportedURIs.Averyinterestingfactisthatnopermissionsareneededforanapplicationtoaccessthisinformation;ifourcontentproviderrequirespermissions,orisnotexported,alltheapplicationscanstillcallthismethodregardlessoftheiraccesspermissionstoretrieveMIMEtypes.
AlltheseMIMEtypesshouldbedeclaredinthecontractclass:
@Override
publicStringgetType(Uriuri){
inturiType=mmURIMatcher.match(uri);
switch(uriType){
caseCONTACTS_TABLE:
returnPersonalContactContract.CONTENT_TYPE;
caseCONTACTS_TABLE_ITEM:
returnPersonalContactContract.CONTENT_ITEM_TYPE;
default:
thrownewIllegalArgumentException("UnknownURI:"+uri);
}
}
AddingaprovidertoamanifestAnotherimportantstepistoaddourcontentprovidertoamanifest,likewedowithotherAndroidcomponents.Wecanregistermultipleprovidershere.Theimportantbithere,otherthanandroid:authorities,isandroid:exported;itdefineswhetherthecontentproviderisavailableforotherapplicationstouse.Incaseoftrue,theproviderisavailabletootherapplications;ifitisfalse,theproviderisnotavailabletootherapplications.IfapplicationshavethesameuserID(UID)astheprovider,theywillhaveaccesstoit:
<provider
android:name="com.personalcontactmanager.provider.PersonalContactProvider"
android:authorities="com.personalcontactmanager.provider"
android:exported="true"
android:grantUriPermissions="true">
</provider>
Anotherimportantconceptispermissions.Wecanaddadditionalsecuritybyaddingreadandwritepermissions,whichtheotherapplicationhastoaddintheirmanifestXMLfileand,inturn,automaticallyinformauserthattheyaregoingtouseaparticularapplication’scontentprovidereithertoread,write,orboth.Wecanaddpermissionsinthefollowingmanner:
android:readPermission="com.personalcontactmanager.provider.READ"
UsingacontentproviderThemainreasonwebuiltacontentproviderwastoallowotherapplicationstoaccessthecomplexdatastoreinourdatabaseandperformCRUDoperations.Wewillnowbuildonemoreapplicationinordertotestournewlybuiltcontentprovider.Thetestapplicationisverysimple,comprisingofonlyoneactivityclassandonelayoutfile.Ithasstandardbuttonstoperformactions.Nothingfancy,justthetoolsforustotestthefunctionalitywejustimplemented.WewillnowdelveintotheTestMainActivityclassandlookintoitsimplementation:
publicclassTestMainActivityextendsActivity{
publicfinalStringAUTHORITY="com.personalcontactmanager.provider";
publicfinalStringBASE_PATH="contacts";
privateTextViewqueryT,insertT;
publicclassColumns{
publicfinalstaticStringTABLE_ROW_ID="_id";
publicfinalstaticStringTABLE_ROW_NAME="contact_name";
publicfinalstaticStringTABLE_ROW_PHONENUM=
"contact_number";
publicfinalstaticStringTABLE_ROW_EMAIL="contact_email";
publicfinalstaticStringTABLE_ROW_PHOTOID="photo_id";
}
Toaccessacontentprovider,weneeddetailssuchasAUTHORITYandBASE_PATHandthenamesofthecolumnsofdatabasetables;weneedtoaccessthepublicclassColumnsforthispurpose.Wehavemoretablesandwewillseemoreoftheseclasses.Generally,allthisnecessaryinformationwillbetakenfromthepublishedcontractclassofthecontentprovider.Somecontentprovidersalsorequireimplementingreadorwritepermissionsinthemanifest:
<uses-permissionandroid:name="AUTHORITY.permission.WRITE_TASKS"/>
Insomecases,thecontentproviderweneedtoaccesscanaskustoaddpermissionsinourmanifest.Whentheusersinstalltheapplication,theywillseeanaddedpermissionintheirpermissionlist:
@Override
protectedvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test_main);
queryT=(TextView)findViewById(R.id.textQuery);
insertT=(TextView)findViewById(R.id.textInsert);
}
NoteTotryoutsomeotherapp’scontentprovider,refertohttp://goo.gl/NEX2hN.
ItlistshowyoucanusetheAny.do’scontentprovider—averyfamoustaskapplication.
WewillsetourlayoutandinitializetheviewswerequireinonCreate()ofactivity.Toquery,wefirstneedtopreparetheURIobjectthatmatchesthetable.
Contentresolvernowcomesintoplay;itactsasaresolverforthecontentURIweprepared.OurgetContentResolver.query()method,inthiscase,willfetchallthecolumnsandrows.Wewillnowmovethecursortothefirstpositioninordertoreadtheresult.Fortestingpurposes,it’sreadasastring:
publicvoidquery(Viewv){
UricontentUri=Uri.parse("content://"+AUTHORITY
+"/"+BASE_PATH);
Cursorcr=getContentResolver().query(contentUri,null,
null,null,null);
if(cr!=null){
if(cr.getCount()>0){
cr.moveToFirst();
Stringname=cr.getString(cr.getColumnIndexOrThrow(
Columns.TABLE_ROW_NAME));
queryT.setText(name);
}
}
....
....
}
Now,webuildaURItoreadaparticularrowinsteadofacompletetable.WealreadymentionedthattomakeURIID-based,weneedtoaddtheIDparttoourexistingcontenturi.Now,webuildourprojectionstringarraytobepassedasaparameterinourquery()method:
publicvoidquery(Viewv){
...
...
UrirowUri=contentUri=ContentUris.withAppendedId
(contentUri,getFirstRowId());
String[]projection=newString[]{
Columns.TABLE_ROW_NAME,Columns.TABLE_ROW_PHONENUM,
Columns.TABLE_ROW_EMAIL,Columns.TABLE_ROW_PHOTOID};
cr=getContentResolver().query(contentUri,projection,
null,null,null);
if(cr!=null){
if(cr.getCount()>0){
cr.moveToFirst();
Stringname=cr.getString(cr.getColumnIndexOrThrow(
Columns.TABLE_ROW_NAME));
queryT.setText(name);
}
}
}
ThegetFirstRowId()methodgetstheIDofthefirstrowinthetable.ItisdonebecausetheIDofthefirstrowwillnotalwaysbe1.Itchangeswhentherowsaredeleted.IfthefirstiteminthetablewithrowID1isdeleted,thentheseconditemwithrowID1becomesthefirstitem:
privateintgetFirstRowId(){
intid=1;
UricontentUri=Uri.parse("content://"+AUTHORITY+"/"
+"contacts");
Cursorcr=getContentResolver().query(contentUri,null,
null,null,null);
if(cr!=null){
if(cr.getCount()>0){
cr.moveToFirst();
id=cr.getInt(cr.getColumnIndexOrThrow(
Columns.TABLE_ROW_ID));
}
}
returnid;
}
Let’stakeacloserlookatthequery()method:
publicfinalCursorquery(Uriuri,String[]projection,Stringselection,
String[]selectionArgs,StringsortOrder)
PresentinAPIlevel1,thequery()methodreturnsacursorovertheresultsetagainsttheparameterswesupplied.Thefollowingaretheparametersoftheprecedingcode:
uri:ThisiscontentURIinourcase,usingthecontent://schemeforthecontenttoberetrieved.ItcanbeID-basedordirectory-based.projection:Thisisalistofthecolumnstobereturnedaswehavepreparedusingthecolumnnames.Passingnullwillreturnallthecolumns.selection:FormattedasaSQLWHEREclause,excludingtheWHEREitself,thisactsasafilterdeclaringwhichrowstoreturn.selectionArgs:Wemayinclude?parametermarkersinselection.AndroidSQLquerybuilderwillreplacethe?parametermarkersbythevaluesboundasstringfromselectionArgs,intheorderthattheyappearintheselection.sortOrder:Thistellsushowtoordertherows,formattedasanSQLORDERBYclause.Anullvaluewillusethedefaultsortorder.
NoteAccordingtoofficialdocumentation,thereareafewguidelinesweshouldfollowfor
optimumperformance:
Provideanexplicitprojectiontopreventreadingdatafromstoragethatisn’tgoingtobeused.Usequestionmarkparametermarkerssuchasphone=?insteadofexplicitvaluesintheselectionparameter,sothatqueriesthatdifferonlybythosevalueswillberecognizedasthesameforcachingpurposes.
Thesameprocessweusedearliertocheckfornullvaluesandanemptycursorisperformed,andfinally,arequiredvalueisextractedfromthecursor.
Now,letuslookattheinsertmethodforourtestapplication.
Westartbybuildingourcontentvalueobjectandrelevantkey-valuepairs,forinstance,puttingaphonenumberintherelevantColumns.TABLE_ROW_PHONENUMfield.Noticethatbecausedetailssuchasacolumn’snameweresharedwithusintheformofaclass,weneednotworryaboutdetailssuchastheactualcolumnname.WejustneedtoaccessitviameansoftheColumnsclass.Thisensuresthatweonlyneedtoupdatetherelevantvalues.Ifinfuturethecontentproviderundergoessomechangeandchangesthetablenames,therestofthefunctionalityandimplementationremainsthesame.Webuildourprojectionstringarraywiththecolumnnameswerequired,aswedidearlierinthecaseofqueryingthecontentproviderfordata.
WealsobuildourcontentURI;noticethatitmatchesthetableandnotindividualrows.Theinsert()methodalsoreturnsaURIunlikethequery()method,whichreturnedacursorovertheresultset:
publicvoidinsert(Viewv){
Stringname=getRandomName();
Stringnumber=getRandomNumber();
ContentValuesvalues=newContentValues();
values.put(Columns.TABLE_ROW_NAME,name);
values.put(Columns.TABLE_ROW_PHONENUM,number);
values.put(Columns.TABLE_ROW_EMAIL,name+"@gmail.com");
values.put(Columns.TABLE_ROW_PHOTOID,"abc");
String[]projection=newString[]{
Columns.TABLE_ROW_NAME,Columns.TABLE_ROW_PHONENUM,
Columns.TABLE_ROW_EMAIL,Columns.TABLE_ROW_PHOTOID};
UricontentUri=Uri.parse("content://"+AUTHORITY+"/"
+BASE_PATH);
UriinsertedRowUri=getContentResolver().insert(
contentUri,values);
//checkingtheaddedrow
Cursorcr=getContentResolver().query(insertedRowUri,
projection,null,null,null);
if(cr!=null){
if(cr.getCount()>0){
cr.moveToFirst();
name=cr.getString(cr.getColumnIndexOrThrow(
Columns.TABLE_ROW_NAME));
insertT.setText(name);
}
}
}
ThegetRandomName()andgetRandomNumber()methodsgeneratearandomnameandnumbertoinsertinthetable:
privateStringgetRandomName(){
Randomrand=newRandom();
Stringname=""+(char)(122-rand.nextInt(26))
+(char)(122-rand.nextInt(26))
+(char)(122-rand.nextInt(26))
+(char)(122-rand.nextInt(26))
+(char)(122-rand.nextInt(26))
+(char)(122-rand.nextInt(26))
+(char)(122-rand.nextInt(26))
+(char)(122-rand.nextInt(26));
returnname;
}
publicStringgetRandomNumber(){
Randomrand=newRandom();
Stringnumber=rand.nextInt(98989)*rand.nextInt(59595)+"";
returnnumber;
}
Let’stakeacloserlookattheinsert()method:
publicfinalUriinsert(Uriurl,ContentValuesvalues)
Thefollowingaretheparametersoftheprecedinglineofcode:
url:TheURLofthetabletoinsertthedataintovalues:ThevaluesforthenewlyinsertedrowintheformofaContentValuesobject,thekeyisthecolumnnameforthefield
Noticethatafterinserting,wearerunningthequery()methodagainwiththeURIthatwasreturnedbytheinsert()method.Werunthistoseethatthevalueweintendedtoinserthasbeeninserted;thisquerywillreturncolumnsaspertheprojectionoftherowwhoseIDisappended.
Sofar,wehavecoveredthequery()andinsert()methods;now,wewillcovertheupdate()method.
Weprogressedintheinsert()methodbypreparingtheContentValuesobject.Similarly,wewillprepareanobjectthatwewilluseintheupdate()methodofContentResolverto
updateanexistingrow.WewillbuildourURIinthiscaseuptotheID,asthisoperationisIDbased.UpdatetherowaspointedbytherowUriobjectanditwillreturnthenumberofrowsupdated,whichwillbethesameastheURI;inthiscase,itisrowUrithatpointstoonlyasinglerow.AnalternatemethodcouldbeusingacombinationofcontentUri(whichpointstothetable)andselection/selectionArgs.Inthiscase,therowsupdatedcouldbemorethanoneaspertheselectionclause:
publicvoidupdate(Viewv){
Stringname=getRandomName();
Stringnumber=getRandomNumber();
ContentValuesvalues=newContentValues();
values.put(Columns.TABLE_ROW_NAME,name);
values.put(Columns.TABLE_ROW_PHONENUM,number);
values.put(Columns.TABLE_ROW_EMAIL,name+"@gmail.com");
values.put(Columns.TABLE_ROW_PHOTOID,"");
UricontentUri=Uri.parse("content://"+AUTHORITY
+"/"+BASE_PATH);
UrirowUri=ContentUris.withAppendedId(
contentUri,getFirstRowId());
intcount=getContentResolver().update(rowUri,values,null,null);
}
Let’stakeacloserlookattheupdate()method:
publicfinalintupdate(Uriuri,ContentValuesvalues,Stringwhere,
String[]selectionArgs)
Thefollowingaretheparametersoftheprecedinglineofcode:
uri:ThisisthecontentURIwewishtomodifyvalues:Thisissimilartothevaluesweusedearlierwithothermethods;passinganullvaluewillremoveanexistingfieldvaluewhere:ASQLWHEREclausethatactsasafiltertorowsbeforeupdatingthem
Wecanrunthequery()methodagaintoseewhetherthechangeisreflected;thisactivityhasbeenleftasanexerciseforyou.
Thelastmethodisdelete(),whichwerequireinordertocompleteourarsenalofCRUDmethods.Thedelete()methodbeginsinasimilarfashionastherestofthemethodsdo;first,prepareourcontentURIatthedirectorylevelandthenbuilditfortheIDlevel,thatis,attheindividualrowlevel.Afterthat,wepassittothedelete()methodofContentResolver.Unlikethequery()andinsert()methodsthatreturnanintegervalue,thedelete()methoddeletesarowaspointedbyourID-basedcontentURIobjectrowUriandreturnsthenumberofrowsdeleted.Thiswillbe1inourcaseasourURIpointstoonlyonerow.AnalternatemethodcouldbeusingacombinationofcontentUri,whichpointstothetable,andselection/selectionArgs.Inthiscase,therowsdeletedcouldbemorethan1aspertheselectionclause:
publicvoiddelete(Viewv){
UricontentUri=Uri.parse("content://"+AUTHORITY
+"/"+BASE_PATH);
UrirowUri=contentUri=ContentUris.withAppendedId(
contentUri,getFirstRowId());
intcount=getContentResolver().delete(rowUri,null,
null);
}
TheUIandoutputlooklikethefollowing:
NoteIfyouwanttodiveinalittlemoreintohowanAndroidcontentprovideractuallymanagesvariouswriteandreadcallsbetweenvarioustables(hint:itusesCountDownLatch),youcancheckoutthevideoatCourserabyDr.DouglasC.Schmidtformoreinformation.Thevideocanbefoundathttps://class.coursera.org/posa-002/lecture/49.
SummaryInthischapter,wecoveredthebasicsofcontentproviders.Welearnedhowtoaccesssystem-providedcontentprovidersandevenourownversionofacontentprovider.Wewentfromcreatingabasiccontactmanagertoevolvingitintoafully-fledgedcitizenoftheAndroidecosystembyimplementingContentProviderinordertosharedataacrossotherapplications.
Inthefollowingchapter,wewillcoverLoaders,CursorAdapters,niftyhacksandtips,andsomeopensourcelibrariestomakeourlifeeasierwhileworkingwiththeSQLitedatabase.
Chapter4.ThreadCarefully “Prematureoptimizationistherootofallevil.”
—-DonaldKnuth
Wecoveredaveryimportantconceptinthepreviouschapter:contentprovider.Weprogressedinastep-by-stepmanner,coveringessentialquestionssuchashowtocreateacontentproviderandhowtouseanexistingsystemwithacontentproviderindetail.Wealsocoveredhowtousethecontentproviderwecreatedbymeansofcreatingatestapplicationtoaccessit.
Inthischapter,wewillexplorehowtouseloaders,inparticular,aloadercalledcursorloader.Wewilllookathowtointeractwithacontentproviderasynchronouslywiththehelpofanexample.WewilldiscusstheimportanttopicofsecurityintheAndroiddatabaseandhowwecanensurethatdataissecuredinanAndroidmodel.Lastbutnotleast,wewillalsoseesomecodesnippetsthatwillcovertopicssuchashowtoupgradeadatabaseandhowtoshipapreloadeddatabasewithourapplication.
Inthischapter,wewillcoverthefollowingtopics:
LoadingdatawithCursorLoaderDatasecurityGeneraltipsandlibraries
LoadingdatawithCursorLoaderCursorLoaderispartoftheloaderfamily.BeforewedivedeepintoanexampleexplaininghowtouseCursorLoader,wewillexploreabitaboutloadersandwhyitisimportantinthecurrentscenario.
LoadersIntroducedinHoneyComb(APIlevel11),loadersservethepurposeofasynchronouslyservingdatainanactivityorfragment.Theneedtohaveloadersarosefrommanythings:callstovarioustime-consumingmethodsonthemainUIthreadinordertofetchdatathatleadstoaclunkyUI,andeveninsomecases,thedreadedANRbox.Thisisdemonstratedinthefollowingscreenshot:
Forexample,themanagedQuery()method,whichwasdeprecatedinAPI11,wasawrapperaroundtheContentResolver'squery()method.
Inthepreviouschapter,whilehighlightinghowtofetchdatafromacontentproviderinsidethequerymethod,weusedgetContentResolver.query()insteadofmanagedQuery().Usingdeprecatedmethodscanleadtoproblemswithfuturereleasesandshouldbeavoided.
Loadersprovideasynchronousloadingofdataforanactivityoffragmentonanon-UIthread.Theloaderorthesubclassesofaloaderperformtheirworkinaseparatethreadanddelivertheirresultstothemainthread.Thesegregationofcallsfromthemainthreadandthepostingofresultsonthemainthreadwhileworkinginaseparatethreadensurethatwehavearesponsiveapplication.
TipPosttheloaderera,wewerefacedwithproblemssuchaswhenanactivityshouldberecreatedduetoaconfigurationchange,forinstance,rotationofadevice’sorientation.Wehadtoworryaboutdataandrefetchdatawhilecreatinganewinstance.Butwithloaders,wedon’thavetoworryaboutalltheseasloadersautomaticallyreconnecttothelastloader’scursorwhenbeingrecreatedafteradeviceconfigurationchangeandrefetchthedata.Asanaddedbonus,loadersmonitorthedatasourceanddelivernewresultswhenthecontentchanges.Inotherwords,loadersautomaticallygetupdated,andhence,thereisnoneedtorequerythecursor.ReadmoreaboutkeepingyourAndroidapplicationresponsiveandavoidingapplicationnotresponding(ANR)messagesattheAndroiddeveloperwebsite,http://developer.android.com/training/articles/perf-anr.html.
LoaderAPI’ssummaryLet’slookattheloaderAPIthatconsistsofvariousclassesandinterfaces.Inthissection,wewilllookattheimplementationaspectofloaderAPI’sclasses/interfaces:
Class/interface Description
LoaderManager
Thisisanabstractclassassociatedwithanactivityorfragmenttomanagealoader.Althoughtherecanbeoneormoreloaderinstances,onlyoneinstanceofLoaderManagerperactivityorfragmentispermitted.Itisresponsiblefordealingwiththeactivityorfragment’slifecycleandparticularlyhelpfulwhenrunninglong-runningtasks.
LoaderManager.LoaderCallbacks ThisisacallbackinterfacewemustimplementtointeractwithLoaderManager.
Loader
Thisisthebaseclassforaloader.It’sanabstractclassthatperformsasynchronousloadingofdata.WecanimplementourownsubclassinsteadofusingsubclassessuchasCursorLoader.
AsyncTaskLoader
ThisisanabstractloaderthatprovidesAsyncTasktoperformtheworkinthebackground,thatis,onaseparatethread;however,theresultisdeliveredonthemainthread.Accordingtothedocumentation,itisadvisedtosubclassAsyncTaskLoaderinsteadofdirectlysubclassingtheLoaderclass.
CursorLoaderThisisasubclassofAsyncTaskLoaderthatqueriesContentResolveronthebackgroundthreadinanon-blockingmannerandreturnsacursor.
UsingCursorLoaderLoadersprovideuswithalotofhandyfeatures;oneofthemisthatonceouractivityorfragmentimplementsaloader,itneednotworryaboutrefreshingthedata.Aloadermonitorsthedatasourceforus,reflectsanychanges,andevenperformsnewloads;allofthisisdoneasynchronously.Hence,wedonotneedtotakecareofimplementingandmanagingthreads,offloadingqueriesonthebackgroundthread,andretrievingresultsoncethequeryiscompleted.
Aloadercanbeinanyoneofthefollowingthreedistinctstates:
Startedstate:Oncestarted,loadersremaininthisstateuntilstoppedorreset.Itexecutesloads,monitorsanychange,andreflectsthesametothelisteners.Stoppedstate:Here,loaderscontinuetomonitorchangesbutdonotpasstheresulttotheclients.Resetstate:Inthisstate,loadersreleaseanyresourcestheyhaveheldanddonotperformtheprocessofexecuting,loading,ormonitoringdata.
WewillnowrelookatourpersonalcontactmanagerapplicationandmakethecorrespondingchangestoimplementCursorLoaderinourapplication.CursorLoader,asthenamesuggests,isaloaderthatqueriesContentResolverandreturnsacursor.ThisisasubclassofAsyncTaskLoaderandperformsthecursorqueryonthebackgroundthreadsothatitdoesnotblocktheapplication’sUI.Inthediagram,youcanseethevariousmethodsofaloadercallbackandhowtheycommunicatewithCursorLoaderandCursorAdapter.
Forimplementingacursorloader,weneedtoperformthefollowingsteps:
1. Tobeginwith,weneedtoimplementtheLoaderManager.LoaderCallbacks<Cursor>interface:
publicclassContactsMainActivityextendsActivityimplements
OnClickListener,LoaderManager.LoaderCallbacks<Cursor>{…}
Then,implementthemethodsthatreflectthedistinctstatesofaloader:onCreateLoader(),onLoadFinished(),andonLoaderReset().
2. Toinitiateaquery,wewillmakeacalltotheLoaderManager.initLoader()method;thisinitializesthebackgroundframework:
getLoaderManager().initLoader(CUR_LOADER,null,this);
TheCUR_LOADERvalueispassedontotheonCreateLoader()method,whichactsasanIDfortheloader.Acalltoinitloader()invokesonCreateLoader(),passingtheIDweusedtocallinitloader():
@Override
publicLoader<Cursor>onCreateLoader(intloaderID,
Bundlebundle)
{
switch(loaderID){
caseCUR_LOADER:
returnnewCursorLoader(this,PersonalContactContract.CONTENT_URI,
PersonalContactContract.PROJECTION_ALL,null,null,null);
default:returnnull;
}
}
3. WeuseaswitchcasetotaketheloaderbasedonitsIDandreturnnullforaninvalidID.WecreateaURIobjectcontentUriandpassitasaparametertotheCursorLoaderconstructor.Apointtonoteisthatwecanimplementacursorloaderusingeitherthisconstructororanemptyunspecifiedcursorloader,CursorLoader(Contextcontext).Also,wecansetvaluesviamethodssuchassetUri(Uri),setSelection(String),setSelectionArgs(String[]),setSortOrder(String),andsetProjection(String[]):
publicCursorLoader(Contextcontext,Uriuri,String[]projection,
Stringselection,String[]selectionArgs,StringsortOrder)
Thefollowingaretheparametersofthepreviouscode:
context:Thisistheparentactivitycontext.uri:WeemploycontentURI,usingthecontent://scheme,toretrievethecontent.ItcanbebasedonanIDordirectory.projection:Thisisalistofcolumnstobereturnedaswearepreparedwiththecolumnnames.Passingnullwillreturnallthecolumns.selection:ThisisformattedasaSQLWHEREclause,excludingtheWHEREitself,actingasafilterdeclaringwhichrowstoreturn.
selectionArgs:Wemayincludequestionmarksintheselection,whichwillbereplacedbythevaluesboundasastringfromselectionArgs,andtheywillappearintheorderoftheirselection.sortOrder:Thistellsushowtoorderrows,formattedasaSQLORDERBYclause.Anullvaluewillusethedefaultsortorder.
4. onCreateLoaderstartsthequeryinthebackground,andwhenthequeryisfinished,thecursorloaderobjectispassedtothebackground’sframework,whichcallsonLoadFinished(),whereweprovideouradapterinstancewiththecursorobjectdata:
@Override
publicvoidonLoadFinished(Loader<Cursor>loader,Cursordata)
{
this.mAdapter.changeCursor(data);
}
5. TheadapterisasubclassofCursorAdapter.InsteadofthetraditionalgetView()method,whichwegetbyextendingBaseAdapter,wehavethebindView()andnewView()methods.WeinflateourlistviewrowlayoutintheviewobjectinnewView,andinbindview,weperformanactionsimilartothegetView()method.Wedefineourlayoutelementsandassociatethemewiththerelevantdata:
publicclassCustomCursorAdapterextendsCursorAdapter
{
...
publicvoidbindView(Viewview,Contextarg1,Cursorcursor)
{
finalImageViewcontact_photo=(ImageView)view
.findViewById(R.id.contact_photo);
...
...
contact_email.setText(cursor.getString(cursor
.getColumnIndexOrThrow(DatabaseConstants.TABLE_ROW_EMAIL)));
setImage(cursor.getBlob(cursor
.getColumnIndex(DatabaseConstants.TABLE_ROW_PHOTOID)),
contact_photo);
}
@Override
publicViewnewView(Contextarg0,Cursorarg1,ViewGrouparg2)
{
finalViewview=LayoutInflater.from(context).inflate(
R.layout.contact_list_row,null,false);
returnview;
}
...
}
6. Thismethodisinvokedwhenthecursorloaderisbeingreset.WeclearoutanyreferencetothecursorbypassingnulltothechangeCursor()method.Wheneverthedataassociatedwithacursorchanges,thecursorloadercallsthismethodbeforeitrerunsthequerytoclearanypastreferences,therebypreventingmemoryleaks.Once
onLoaderReset()isset,thecursorloaderwillrerunitsquery:
@Override
publicvoidonLoaderReset(Loader<Cursor>loader)
{
this.mAdapter.changeCursor(null);
}
7. Nowwemoveontoourcontentproviderwherewehavetomakesmallchangestoensurethatanychangeswemaketothedatabasearereflectedinourapplication’slistview:
cr.setNotificationUri(getContext().getContentResolver(),uri);
8. WeneedtoregisterobserverinContentResolverthroughthecursorinthequerymethodofContentProvider.WedothistowatchthecontentURIforanychanges,whichcanbetheURIofaspecificdatarowortableinourcase:
getContext().getContentResolver().notifyChange(ur,null);
9. Intheinsert()method,weusethenotifyChange()methodtoinformregisteredobserversthatarowwasupdated.Bydefault,theCursorAdapterobjectswillgetthisnotification.So,nowwhenweaddanewrowofdatabyinsertinganewcontactinourapplication,theinsert()methodofcontentProviderisinvokedviaacall:
resolver.insert(PersonalContactContract.CONTENT_URI,
prepareData(contact));
10. Asimilaractionneedstobeperformedforthedelete()andupdate()methods,bothofwhichhavebeenleftasanexerciseforthereaderasmostoftheboilerplatecodeispresent.Implementingaloaderissimpleandsavesusfromalotofheadachewhenitcomestothreading,andajarringUIishighlyrecommendedtoperformthistask.
NoteloadInBackground()isanotherimportantmethod;thisreturnsacursorinstanceforaloadoperationandiscalledontheworkerthread.Ideally,loadInBackground()shouldnotdirectlyreturntheresultoftheloadoperation,butwecanachievethisbyoverridingthedeliverResult(D)method.Tocancel,weneedtocheckthevalueofisLoadInBackgroundCanceled()aswedointhecaseofAsyncTask,wherewecheckisCancelled()periodically.
DatasecuritySecurityisthelatestbuzzwordintown.TheAndroidecosystemensuresthatourdatabaseisexposedtopryingeyes;however,arooteddevicecanleaveourdatabaseexposed,aswesawinChapter2,ConnectingtheDots.Withthehelpofarooteddevice,anemulatorandtheadbpullcommandinourcase,wepulledourdatabaseforinspectionwiththeSQLitemanagertool.Anotherimportantaspectiscontentproviders;weneedtobecarefulwhilesettingpermissions.Weshouldmaketheprocessofapplyingappropriatepermissionscompulsoryinordertoinformusersaboutthecontrolthatanappestablishesoverdata,usingthecontractclass.
ContentProviderandpermissionsInChapter3,SharingisCaring,webrieflycoveredthetopicofpermissionsintheAddingaprovidertoamanifestsection.Let’selaboratealittlemoreonthis:
1. Asmentionedearlier,whileaddingthecontentprovidertothemanifest,wewillalsoaddourcustompermissions.Thiswillensuretwothings,namely,stopanunauthorizedactioninanapplicationandinformtheusersaboutpermissions:
<provider
android:name="com.personalcontactmanager.provider.PersonalContactProvid
er"
android:authorities="com.personalcontactmanager.provider"
android:readPermission="com.personalcontactmanager.provider.read"
android:exported="true"
android:grantUriPermissions="true"
>
2. Additionally,wewilladdthepermissionstagtothemanifesttoindicatethesetofpermissionsthatotherapplicationswillrequire:
<permission
android:name="com.personalcontactmanager.provider.read"
android:icon="@drawable/ic_launcher"
android:label="ContactManager"
android:protectionLevel="normal">
</permission>
3. Now,intheapplicationinwhichwewanttoaccessthecontentproviderweusethepermissiontag,inourcase,Ch4-TestAppincodebundle:
<uses-permission
android:name="com.personalcontactmanager.provider.read"/>
Whenusersinstallthisapplication,theywillgetourcustompermissionmessagealongwithotherpermissionsrequiredbytheapplication.Forthisstep,insteadofdirectlyrunningtheapplicationfromEclipse,exportanapkandinstallit:
Ifyouhavenotdefinedthepermissionintheapplicationandiftheapplicationtriestoaccessthecontentprovider,itwillgettheSecurityException:PermissionDenialmessage.
Ifthecontentproviderwecreatedisnotmeanttobeshared,wewillneedtochangetheandroid:exported="true"propertytofalse.Thiswillmakeourcontentprovidersecure,andifsomeonetriestorunamaliciousqueryonit,theywillencounterasecurityexception.
Ifwewanttosharedataonlybetweenourapplications,Androidprovidesasolution;wecanuseandroid:protectionLevelandsetthepermissiontosignatureinsteadofnormal.Forthis,boththeapps,theonethatimplementsthecontentproviderandtheonethatwantstoaccessit,havetobesignedbythesamekeywhiletheyareexported.Thisisbecauseabonussignaturepermissiondoesnotrequireuserconfirmation.Thisdoesnotconfusetheuserasitisdoneinternallyandalsodoesnotobstructtheuserexperience.
EncryptingcriticaldataWehavealreadydiscussedwhatkindofaccessrightsotherapplicationshaveonourdatabaseandhowtoefficientlyshareourcontentproviders,andwealsobrieflydiscussedwhyweshouldnotbelievethatthesystemisfoolproof.Inthemostfoolproofmethod,sensitivedatawillnotbekeptonthedevicebutontheserverinstead,anditwillusetokenstogiveaccess.Ifyouhavetostorethedataonthedevice’sdatabase,useencryption.Useauser-definedkeytoencryptanddecryptsensitivedata.
Wewillexploreawaytouseanencrypteddatabase,whichwillnotbereadableifsomeoneisabletoextractitviameansofarootorviaexploitingbackups.IfsomeonetriestoreaditusingSQLiteManagerorsomeothertool,theywillreceiveafriendlymessage,suchastheoneshowninthefollowingscreenshot;thisisthedatabasefilethatwewillcreateinamomentwithalibraryknownasSQLCipher.
SQLCipherisanopensourceextensiontoSQLitethatprovidesatransparent256-bitAESencryptionofdatabasefiles,asmentionedontheirwebsite.ItisveryeasytodeploySQLCipher.Nowwe’lllookatthestepstobuildasampleapplication:
1. First,wewilldownloadthenecessaryfilesfromhttp://sqlcipher.net/open-source.Here,theyhavelistedacommunityeditionoftheAndroid-basedSQLCipher;downloadit.
2. NowwewillcreateanewAndroidprojectinoureclipseenvironment.3. Insidethedownloadedfolder,wewillfindthelibsfolder;insideit,areasetofjars
thatwewillneedtoworkwithSQLCipher.Wewillalsonoticethatfoldersarenamedasarmeabi,armeabi-v7a,andx86,andallofthesecontainthe.sofiles.IfyouarefamiliarwithAndroidNDK,thiswillnotseemnew.The.sofileisasharedobjectfile,whichisacomponentofdynamiclibraries.Fordifferentarchitectures,werequiredifferent.sofiles,hencethethreefolders.Ifyouarerunninganx86emulator,youwillneedthex86folderinyourlibsfolder.Forsimplicity,wewillcopyallthefolderstothelibsfolder.Copytheassetfolder’scontentintoourproject’sassetfolderandnavigatetotheproject’sproperties.Itwilllooksomethinglikethefollowingscreenshot.YoucanalsoseetheseJARfilesintheproject’sclasspath.Theinitialsetupforthisprojectisnowcomplete.
Aftercompletingthenecessarysetuppart,let’smovetowritingcodetomakeasmalltestapplication:
publicclassMainActivityextendsActivity
{
TextViewshowResult;
@Override
protectedvoidonCreate(BundlesavedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
showResult=(TextView)findViewById(R.id.showResult);
InitializeSQLCipher();
}
privatevoidInitializeSQLCipher()
{
SQLiteDatabase.loadLibs(this);
FiledatabaseFile=getDatabasePath("test.db");
databaseFile.mkdirs();
databaseFile.delete();
SQLiteDatabasedatabase=SQLiteDatabase
.openOrCreateDatabase(databaseFile,"test123",null);
database.execSQL("createtablet1(a,b)");
database.execSQL("insertintot1(a,b)values(?,?)",
newObject[]{"Iam","Encrypted"});
}
publicvoidrunQuery(Viewv)
{
FiledatabaseFile=getDatabasePath("test.db");
SQLiteDatabasedatabase=SQLiteDatabase.openOrCreateDatabase(
databaseFile,"test123",null);
Stringselection="select*fromt1";
Cursorc=database.rawQuery(selection,null);
c.moveToFirst();
showResult.setText(c.getString(c.getColumnIndex("a"))+
c.getString(c.getColumnIndex("b")));
}
}
Theprecedingcodehastwomainmethods:InitializeSQLCipher()andrunQuery().InsideInitializeSQLCipher(),weloadour.solibraryfilesbyinvokingtheloadLibs()method.
4. Nowwefindtheabsolutepathtothedatabaseandcreateamissingparentfolderifany.WithopenOrCreateDatabase(),wewillmakeacalltoopenanexistingdatabaseorcreateoneifthedatabaseisnonexistent.Wewillexecutestandarddatabasecallstocreateatablewithcolumnsaandbandinsertvaluesinarow.
NowwewillperformasimplequerytofetchthevaluesbacktotherunQuery()method.Youwillnoticethatapartfromloadingthelibrary,allthecoremethodsweusedareprettymuchstandard,sowhereisthemajorchange?GototheCh4-PersonalContactManagerexampleinthecodebundleandnoticethepackageswehaveused:
importandroid.database.Cursor;
importandroid.database.sqlite.SQLiteDatabase;
WehaveSQLCipherpackages:
importnet.sqlcipher.Cursor;
importnet.sqlcipher.database.SQLiteDatabase;
Theimplementationissimple,familiar,andeasytoimplement.Ifyoupullthedatabaseoutandtrytoreadit,youwillfindtheerrormessage,aswedisplayedearlierinascreenshot.Theuserwillfindnochange,andevenourapp’slogicremainsthesame.Inthescreenshot,youcanseetheapplicationscreenwejustbuiltwhichencryptsthedatabase:
NoteOAuthisanopenstandardforauthorization.Itprovidesclientapplicationswithasecuredelegatedaccesstoserverresourcesonbehalfofaresourceowner.Itspecifiesaprocessforresourceownerstoauthorizethird-partyaccesstotheirserverresourceswithoutsharingtheircredentials,asexplainedinWikipedia;readmoreaboutOAuthathttp://oauth.net/2/.
GeneraltipsandlibrariesWewillcoversomegeneralandnotsogeneralworkaroundsandpractices,whichcanbeputtogoodusedependingonthesituation.Forinstance,insomecases,weneedtohaveaprepopulateddatabaseofvaluesthatwewillmakeuseofinourAndroidapplicationorupgradingadatabase,whichseemstrivialbutcanbreakourapplication.
UpgradingadatabaseInChapter2,ConnectingtheDots,weusedonUpgrade()toshowhowadatabaseisupdated.Ifwegobacktotheexample,youwillnoticethatitexecutesaDropTablecommand.Whatwillhappenhereisthattheoriginaltablewillbedroppedandanewtablewillbecreatedbythecall,onCreate().Thiswillleadtoalossoftheexistingdataandhenceisnotsuitableifweneedtoalterourdatabase.TheonUpgrade()functioncanbedefinedasfollows:
publicvoidonUpgrade(SQLiteDatabasedb,intoldVersion,intnewVersion)
{
StringDROP_TABLE="DROPTABLEIFEXISTS"+TABLE_NAME;
db.execSQL(DROP_TABLE);
onCreate(db);
}
Onemorechallengeistoidentifytheversionweareusinghere.Theusermightberunningolderversionsoftheapplication,sowehavetokeepinmindthedifferentversionsthatanapplicationhasandwhetherthoseversionswouldbringaboutanychangesinthedatabase.Foranewuser,weneednotworrybecauseifthedatabasedoesnotexist,onCreate()willbecalled.
Tomakesurewehaveaproperupgrade,wewillusetheDB_VERSIONconstantinourCustomSQLiteOpenHelperclasstotellouronUpgrade()methodabouttheactiontobetaken:
privatestaticfinalintDB_VERSION=1;
WewillchangetheDB_VERSIONconstantto3toreflecttheupgrade:
privatestaticfinalintDB_VERSION=3;
Theconstructorwilltakecareoftherest:
publicCustomSQLiteOpenHelper(Contextcontext)
{
super(context,DB_NAME,null,DB_VERSION);
}
Whenthesuperclassconstructorisrun,itcomparestheDB_VERSIONconstantofthestoredSQLite.dbfileagainsttheDB_VERSIONwepassedasaparameterandcallstheonUpgrade()methodifneeded:
publicvoidonUpgrade(SQLiteDatabasedb,intoldVersion,intnewVersion)
{
switch(oldVersion){
case1:db.execSQL(DATABASE_CREATE_MAIN_TABLE);
case2:db.execSQL(DATABASE_CREATE_MAIN_TABLE);
case3:db.execSQL(DATABASE_CREATE_DEL_TABLE);
}
}
InsideouronUpgrade()method,wehaveaswitchcasetomakechanges.Noticethatwedonotusethebreakstatementbecausetheusercanbeonanolderversionandmaynothaveupdatedtheapplication,asexplainedearlier.Forinstance,let’sconsiderthatauserisonaparticularversionofanapplicationthatisrunningDB_VERSION=1andheorsheskipsthenextupdatethatcontainedDB_VERSION=2,andeventually,anewversionoftheapplicationwithDB_VERSION=3isreleased.Now,wehaveacasewheretheuserisstillusinganolderversionoftheapplicationandhasnotinstalledthenewupdateswehavereleased.So,inthiscase,whentheuserinstallstheapplication,theonUpgrade()methodwillfirstexecutecase1andthengotocase2toinstallupdatesthattheusermissed;finally,theuserwillinstalltheupdatesofthethirdversion,ensuringthatallthedatabasechangesarereflected.Noticethatthereisnobreakstatement.Thisisbecausewewanttorunallthecaseswheretheswitchstatementobtainsthevalue1andthelasttwostatementswheretheswitchcaseobtainsthevalue2.
Alternatively,wecanalsousetheifstatement.ThiswillalsobehaveasweintendedasourtestDB_VERSIONconstantwas1,whichwillsatisfyboththeconditionsandreflectthechanges:
if(oldVersion<2){db.execSQL(DATABASE_CREATE_MORE_TABLE);}
if(oldVersion<3){db.execSQL(DATABASE_CREATE_DEL_TABLE);}
DatabaseminusSQLstatementsInmostpartsofthebook,welookedaroundfornooksandcornersofAndroidandSQLite.Forsome,writingSQLstatementswouldbejustanotherdayintheoffice,whileforsome,itwillcomeacrossasaroller-coasterride.ThissectionwillcoveralibrarythatenablesustosaveandretrieveSQLitedatabaserecordswithoutwritingasingleSQLstatement.ActiveAndroidisanactiverecord-styleSQLitepersistenceforAndroid.Accordingtothedocumentation,eachdatabaserecordiswrappedneatlyintoaclasswithmethodssuchassave()anddelete().WewillbeusingtheexampleintheActiveAndroiddocumentationandbuildaworkingsamplebasedonit.Let’slookatthestepsrequiredtogetitupandrunning.
Havealookattheofficialsite,http://www.activeandroid.com/,foranoverviewanddownloadthefilesfromhttp://goo.gl/oW2kod.
Onceyoudownloadthefile,runantontherootfoldertobuildtheJARfile.Onceyourunant,youwillfindyourJARfileinthedistfolder.InEclipse,makeanewproject,addtheJARfiletothelibsfolderoftheproject,andthenaddtheJARfiletotheJavaBuildPathintheprojectproperties.
ActiveAndroidlooksoutforsomeglobalsettingsconfiguredbyperformingthefollowingsteps:
1. Wewillstartbycreatingaclass,extendingtheapplicationclass:
publicclassMyApplicationextendscom.activeandroid.app.Application
{
@Override
publicvoidonCreate()
{
super.onCreate();
ActiveAndroid.initialize(this);
}
@Override
publicvoidonTerminate()
{
super.onTerminate();
ActiveAndroid.dispose();
}
}
2. Nowwewilladdthisapplicationclasstoourmanifestfileandaddmetadatacorrespondingtoourapplication:
<application
android:name="com.active.android.MyApplication">
<meta-data
android:name="AA_DB_NAME"
android:value="test.db"/>
<meta-data
android:name="AA_DB_VERSION"
android:value="1"/>
………..
</application>
3. Withthisbasicsetupcomplete,wewillnowproceedontocreatingourdatamodel.TheActiveAndroidlibrarysupportsannotationandwewilluseitinthefollowingmodelclasses:
//Categoryclass
@Table(name="Categories")
publicclassCategoryextendsModel
{
@Column(name="Name")
publicStringname;
}
//Itemclass
@Table(name="Items")
publicclassItemextendsModel
{
//Ifnameisomitted,thenthefieldnameisused.
@Column(name="Name")
publicStringname;
@Column(name="Category")
publicCategorycategory;
publicItem()
{
super();
}
publicItem(Stringname,Categorycategory)
{
super();
this.name=name;
this.category=category;
}
}
NoteIfyouwanttoexploreannotationsandusetheminyourprojectandreduceboilerplatecode,youcancheckoutthefollowinglibrariesforAndroid:AndroidAnnotations,Square’sDagger,andButterKnife.
4. Toaddanewcategoryoritem,weneedtomakeacalltosave().Inthecodesegment,wecanseethatanitemobjectiscreatedandassociatedwithaparticularcategory,andintheend,save()iscalled:
publicvoidinsert(Viewv)
{
ItemtestItem=newItem();
testItem.category=testCategory;
testItem.name=editTextItem.getText().toString();
testItem.save();
}
Todeleteanitem,wecancallitem.delete().Similarly,tofetchvalues,wehaverelevantmethodsaswell.Thefollowingisacalltofetchallofthedataforaparticularcategory:
List<Item>getall=newSelect().from(Item.class)
.where("Category=?",testCategory.getId())
.orderBy("NameASC").execute();
ThereislotmoretobeexploredinActiveAndroid.Theyhaveschemamigrationandtypeserialization;inadditiontothis,youcanshipaprepopulateddatabasebyplacingthedatabaseintheassetfolder,andyoucanusecontentprovidersaswell.Inshort,itisawell-builtlibraryforpeoplelookingforindirectwaystocommunicatewiththedatabaseandperformdatabaseoperations.IthelpsinaccessingthedatabaseinthefamiliarformofJavamethodsinsteadofpreparingSQLstatementstoperformthesameaction.Thecompletesamplecodeisbundledinthechapter4codebundle.
ShippingwithaprepopulateddatabaseWewillbuildadatabaseandputitinsideourassetfolder,whichisaread-onlydirectory.Atruntime,wewillcheckwhetheradatabaseexists.Ifnot,wewillcopyourdatabasefromtheassetfolderto/data/data/yourpackage/databases.InChapter2,ConnectingtheDots,weusedatoolcalledSQLiteManager;havealookatthethirdscreenshotofthechapter.Wearegoingtousethesametooltobuildourdatabasenow.Ifyoupullyourdatabaseasexplainedinthatsectionorlookatthatscreenshot,youwillnoticeafewmoretablesalongwithyourdatabasetable:
Thestepstobefollowedtocreateaprepopulateddatabaseareasfollows:
1. Tomakeaprepopulateddatabase,weneedtocreateatablenamedandroid_metadataapartfromthetablewerequire.UsingtheSQLiteManagertool,wewillcreateanewdatabasenamedcontact,thenwewillcreatetheandroid_metdatatable:
CREATETABLE"android_metadata"("locale"TEXTDEFAULT'en_US')
2. Wewillinsertarowinthetable:
INSERTINTO"android_metadata"VALUES('en_US')
3. Nowwewillcreatethetableswerequire,inourcase,contact_tableusingtheSQLqueryweusedinChapter2,ConnectingtheDots.IntheDatabaseManagerclass,wewilljustreplacetheconstantswiththeactualvalues:
CREATETABLE"contact_table"("_id"integerprimarykeyautoincrement
notnull,"contact_name"textnotnull,"contact_number"textnot
null,"contact_email"textnotnull,"photo_id"BLOB)
ItisnecessarytorenametheprimaryIDfieldofourtablesto_idifitisnotalreadydefined.ThishelpsAndroidinidentifyingwheretobindtheIDfieldofourtables.
4. Letusfillafewrowsofdata.WecandothisbyrunningtheInsertqueryormanuallytypinginthevaluesusingthetool.Now,copythedatabasefileintotheassetfolder.
5. Now,inouroriginalpersonalcontactmanager,wewillmodifyourDatabaseManagerclass.Thegoodpartisthatthisistheonlyclassweneedtomodifyandtherestofthesystemwillworkasintended.
6. WhentheapplicationrunsandcreatesanewDatabaseManagerclassbypassingthecontext,wewillmakeacalltocreateDatabase()inwhichfirstofallwewillcheckwhetherthedatabasealreadyexists:
PrivateBooleancheckDataBase()
{
SQLiteDatabasecheckDB=null;
try{
StringmyPath=DB_PATH+DB_NAME;
checkDB=SQLiteDatabase.openDatabase(myPath,null,
SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteExceptione){
//databasedoesn'texistyet.
}
if(checkDB!=null){
checkDB.close();
}
returncheckDB!=null?true:false;
}
7. Ifitdoesn’t,wewillcreateanemptydatabasethatwewillreplacewithourdatabase,whichwecopiedintoourassetfolder.Aftercopyingthedatabasefromtheassetfolder,wewillcreateanewSQLiteDatabaseobject:
privatevoidcopyDataBase()throwsIOException
{
InputStreammyInput=myContext.getAssets().open(DB_NAME);
StringoutFileName=DB_PATH+DB_NAME;
OutputStreammyOutput=newFileOutputStream(outFileName);
byte[]buffer=newbyte[1024];
intlength;
while((length=myInput.read(buffer))>0){
myOutput.write(buffer,0,length);
}
myOutput.flush();
myOutput.close();
myInput.close();
}
AnotherpointtonoteisthattheonCreate()methodofourCustomSQLiteOpenHelperclasswillbeemptyaswearenotcreatingadatabaseandtables,butwearecopyingone.Thesamplecodeisbundledinthechapter4codebundle.Ifthisprocesslookstedious,don’tworry;theAndroiddevelopers’communityhasasolutionforyou.SQLiteAssetHelperisanAndroidlibrarythatwillhelpyouinmanagingdatabasecreationandversionmanagement,usinganapplication’srawassetfiles.
Toimplementthis,wehavetofollowafewsimplesteps:
1. CopytheJARfileintoourproject’slibsfolder.2. AddalibrarytoJavaBuildPath.3. Copyourzippeddatabasefileintotheassetfolderof
projectassets/databases/your_database.db.zip.4. TheZIPfileshouldcontainonlyonedbfile.5. Insteadofextendingtheframework’sSQLiteOpenHelperclass,wewillextendthe
SQLiteAssetHelperclass.
6. Theyalsoprovideyouwithassistancetoupgradethedatabasefile,whichneedstobeplacedinassets/databases/<database_name>_upgrade_<from_version>-<to_version>.sql.
7. Thelibrary,documentation,anditscorrespondingsamplecanbefoundathttp://goo.gl/8XSSmR.
SummaryWecoveredamyriadofadvancedtopicsinthischapter,rangingfromloaderstothesecurityofdata.Weimplementedourcursorloadertounderstandhowaloaderworksmagicforourapplications,andwedelvedintosecuringourdatabaseandunderstandingtheconceptofpermissionswhileexposingourcontentprovidertootherapplications.Wealsocoveredsometipssuchasshippingwithaprepopulateddatabase,upgradingadatabasewithoutbreakingthesystem,andusingdatabasequerieswithoutusingSQLcommands.ThisisinnowaytheonlysetofthingswecanachievewithdatabaseandAndroid.Thischapteronlyservesasanudgetowardsthevastprogrammingpossibilitiesoutthere.
IndexA
Activeandroidabout/DatabaseminusSQLstatementsURL/DatabaseminusSQLstatementsglobalsettings,configuring/DatabaseminusSQLstatements
addRow()method/BuildingtheInsertqueryaddURI()method
about/CreatingUriMatcherdefinitionsaffinity/BuildingblocksAheadofTime(AOT)
about/SQLiteinAndroidAndroid
storage/SQLiteinAndroidandroid.database.SQLitepackage
about/DatabasepackagesAndroiddeveloperwebsite
URL/LoadersAPIs
about/APIsApplicationA
about/Whatisacontentprovider?ApplicationB
about/Whatisacontentprovider?applicationnotresponding(ANR)/Loadersarchitecture,SQLite
interface/TheSQLiteinterfaceSQLcompiler/TheSQLcompilervirtualmachine/Thevirtualmachinebackend/TheSQLitebackend
ARTabout/SQLiteinAndroid
AUTOINCREMENTkeyword/Buildingblocks
BB-trees
about/TheSQLitebackendbackend,SQLite
about/TheSQLitebackendB-trees/TheSQLitebackendPager/TheSQLitebackendOSInterface/TheSQLitebackend
BLOBclassabout/Storageclasses
Booleandatatypeabout/TheBooleandatatype
branchtestcoveragereferencelink/WhySQLite?
buildingblocks,Android/Buildingblocks
Ccase-insensitive
about/TheSQLitesyntaxclose()method
about/TheSQLiteOpenHelperclasscolumnconstraint
about/BuildingblocksURL/Buildingblocks
columnconstraint,SQLiteNOTNULLconstraint/BuildingblocksDEFAULTconstraint/BuildingblocksUNIQUEconstraint/BuildingblocksPRIMARYkey/BuildingblocksCHECKconstraint/BuildingblocksAUTOINCREMENTkeyword/Buildingblocks
constraintabout/WhatisanSQLitestatement?
content$//URIabout/UnderstandingcontentURIs
contentproviderabout/Whatisacontentprovider?using/Usingexistingcontentproviders,UsingacontentproviderContentResolverobject/Whatisacontentresolver?creating/CreatingacontentprovidercontentURI/UnderstandingcontentURIscontractclass,declaring/DeclaringourcontractclassURIMatcher,creating/CreatingUriMatcherdefinitionsinitializing,onCreate()methodused/InitializingtheproviderthroughtheonCreate()methodadding,tomanifest/Addingaprovidertoamanifest
/ContentProviderandpermissionsContentResolverobject
about/Whatisacontentresolver?contentURI
about/UnderstandingcontentURIsContentValues
about/ContentValuescontext
about/TheSQLiteOpenHelperclasscontractclass
declaring/Declaringourcontractclasscreatequery
building/BuildingtheCreatequery
CREATETABLEcommandabout/WhatisanSQLitestatement?attributes/WhatisanSQLitestatement?
criticaldata,datasecurityencrypting/Encryptingcriticaldata
CursorLoaderused,forloadingdata/LoadingdatawithCursorLoaderusing/UsingCursorLoaderstartedstate/UsingCursorLoaderstoppedstate/UsingCursorLoaderresetstate/UsingCursorLoaderimplementing/UsingCursorLoader
Cursorobjectabout/Cursor
Cursorquery(Uriuri,String[]projection,Stringselection,String[]selectionArgs,StringsortOrder)method/Creatingacontentprovider
DDalvikvirtualmachine(DVM)
about/SQLiteinAndroiddata
loading,withCursorLoader/LoadingdatawithCursorLoaderdata,loading
CursorLoader,using/UsingCursorLoaderdata,loadingwithCursorLoader
loaders,using/LoadersloaderAPI/LoaderAPI’ssummary
databaseabout/AquickreviewofdatabasefundamentalsSQLitestatement/WhatisanSQLitestatement?SQLitesyntax/TheSQLitesyntaxUI,connectingwith/ConnectingtheUIanddatabaseupgrading/Upgradingadatabaseprepopulateddatabase,creating/Shippingwithaprepopulateddatabase
databasehandler/Adatabasehandlerandqueriesdatabasepackages
about/DatabasepackagesAPIs/APIsSQLiteOpenHelperclass/TheSQLiteOpenHelperclassSQLiteDatabaseclass/TheSQLiteDatabaseclassContentValues/ContentValuesCursorobject/Cursor
datasecurityabout/Datasecuritycontentprovider/ContentProviderandpermissionspermissions/ContentProviderandpermissionscriticaldata,encrypting/Encryptingcriticaldata
datatypes,SQLiteabout/DatatypesinSQLitestorageclasses/StorageclassesBooleandatatype/TheBooleandatatypeDatedatatype/TheDateandTimedatatypeTimedatatype/TheDateandTimedatatype
Datedatatypeabout/TheDateandTimedatatype
DEFAULTconstraint/Buildingblocksdelete()method/TheSQLiteDatabaseclass
used,fordeletingrecords/Deletingrecordsthroughthedelete()methoddelete()method,SQLiteDatabase/BuildingtheDeletequeryDELETEcommand
about/Aquickreviewofdatabasefundamentalsdeletequery
building/BuildingtheDeletequerydeleteRow()method/ConnectingtheUIanddatabasedelRowmethod/ConnectingtheUIanddatabasedynamictyping/Buildingblocks
EEclipse
emulator,settingup/Buildingblocksemulator
about/Buildingblocksemulator,Eclipse
settingup,steps/Buildingblocksexternalstorage
about/SQLiteinAndroid
Ffeatures,SQLite
zero-configuration/WhySQLite?no-copyright/WhySQLite?cross-platform/WhySQLite?compact/WhySQLite?foolproof/WhySQLite?
GGenymotion
URL/Buildingblocksget*()methods
about/CursorgetBlob()method/ConnectingtheUIanddatabasegetCount()method
about/CursorgetRandomName()method/UsingacontentprovidergetRandomNumber()method/UsingacontentprovidergetReadableDatabase()method
about/TheSQLiteOpenHelperclassgetType()method
used,forgettingreturntypeofcontent/GettingthereturntypeofdatathroughthegetType()method
getView()method/ConnectingtheUIanddatabasegetWriteableDatabase()method
about/TheSQLiteOpenHelperclass
IIllegalArgumentException/Queryingrecordsthroughthequery()methodinsert()method
used,foraddingrecords/Addingrecordsthroughtheinsert()methodurlparameter/Usingacontentprovidervaluesparameter/Usingacontentprovider
INSERTcommandabout/Aquickreviewofdatabasefundamentals
insertquerybuilding/BuildingtheInsertquery
intdelete(Uriuri,Stringselection,String[]selectionArgs)method/CreatingacontentproviderINTEGERclass
about/Storageclassesinterface,SQLite
about/TheSQLiteinterfaceinternalstorage
about/SQLiteinAndroidintupdate(Uriuri,ContentValuesvalues,Stringselection,String[]selectionArgs)method/CreatingacontentproviderisAfterLast()method
about/CursorisReadOnly()method
about/TheSQLiteOpenHelperclass
JJustinTime(JIT)
about/SQLiteinAndroid
LLemonparsergenerator
URL/TheSQLcompilerLoaderAPI
classes/interfaces/LoaderAPI’ssummaryloaders
about/LoadersloadInBackgroundmethod/UsingCursorLoader
MmoveToFirst()method
about/CursormoveToNext()method
about/Cursor
NNOTNULLconstraint/BuildingblocksNULLclass
about/StorageclassesNullPointerException/Queryingrecordsthroughthequery()method
OOAuth
URL/EncryptingcriticaldataonContextItemSelected()method/ConnectingtheUIanddatabaseonCreate()method/BuildingtheCreatequery
about/TheSQLiteOpenHelperclassused,forinitializingcontentprovider/InitializingtheproviderthroughtheonCreate()method
onOpen()methodabout/TheSQLiteOpenHelperclass
onUpgrade()methodabout/TheSQLiteOpenHelperclass
/BuildingtheCreatequeryOSInterface
about/TheSQLitebackend
PPager
about/TheSQLitebackendpath
about/UnderstandingcontentURIspermissions/Addingaprovidertoamanifest,ContentProviderandpermissionsprepareData()method/BuildingtheInsertqueryprepareSendData()method/ConnectingtheUIanddatabaseprepopulateddatabase
shipping/Shippingwithaprepopulateddatabasecreating/Shippingwithaprepopulateddatabase
PRIMARYkey/Buildingblocks
Qquery
about/Aquickreviewofdatabasefundamentals,Adatabasehandlerandqueriescreatequery,building/BuildingtheCreatequeryinsertquery,building/BuildingtheInsertquerydeletequery,building/BuildingtheDeletequeryupdatequery,building/BuildingtheUpdatequery
query()methodused,forqueryingrecords/Queryingrecordsthroughthequery()methoduriparameter/Usingacontentproviderprojectionparameter/Usingacontentproviderselectionparameter/UsingacontentproviderselectionArgsparameter/UsingacontentprovidersortOrderparameter/Usingacontentprovider
RREALclass
about/Storageclassesresetstate,CursorLoader/UsingCursorLoader
SSELECTcommand
about/Aquickreviewofdatabasefundamentalssharedpreference
about/SQLiteinAndroidSQLCipher
about/EncryptingcriticaldataURL/Encryptingcriticaldatasampleapplication,steps/Encryptingcriticaldata
SQLcompilerabout/TheSQLcompiler
SQLiteabout/WhySQLite?using/WhySQLite?features/WhySQLite?architecture/TheSQLitearchitecturedatatypes/DatatypesinSQLite
SQLite3about/SQLiteversion
SQLite3command.dump/SQLiteversion.schema/SQLiteversion.help/SQLiteversion
SQLiteDatabase()querymethod/BuildingtheInsertquerySQLiteDatabaseclass
about/TheSQLiteDatabaseclassURL,fordocumentation/TheSQLiteDatabaseclass
SQLiteinAndroidabout/SQLiteinAndroidversion/SQLiteversiondatabasepackages/Databasepackages
SQLiteManagertoolURL/BuildingtheCreatequery
SQLiteOpenHelperclassabout/TheSQLiteOpenHelperclass
SQLitestatementabout/WhatisanSQLitestatement?INSERT/WhatisanSQLitestatement?SELECT/WhatisanSQLitestatement?UPDATE/WhatisanSQLitestatement?DELETE/WhatisanSQLitestatement?ALTER/WhatisanSQLitestatement?DROP/WhatisanSQLitestatement?
SQLstatementstips/DatabaseminusSQLstatements
startedstate,CursorLoader/UsingCursorLoaderstoppedstate,CursorLoader/UsingCursorLoaderstorage,Android
sharedpreference/SQLiteinAndroidexternalstorage/SQLiteinAndroidinternalstorage/SQLiteinAndroid
storageclassesabout/StorageclassesNULL/StorageclassesINTEGER/StorageclassesREAL/StorageclassesTEXT/StorageclassesBLOB/Storageclasses
StringgetType(Uri)method/Creatingacontentprovidersynchronizedkeyword
about/TheSQLiteOpenHelperclasssyntax,SQLite
about/TheSQLitesyntax
TTEXTclass
about/StorageclassesTextUtils.isEmpty()method/ConnectingtheUIanddatabaseTimedatatype
about/TheDateandTimedatatypetips,prepopulateddatabase/Generaltipsandlibraries
UUI
connecting,withdatabase/ConnectingtheUIanddatabaseUNIQUEconstraint/Buildingblocksupdate()method/TheSQLiteDatabaseclass
used,forupdatingrecords/Updatingrecordsthroughtheupdate()methoduriparameter/Usingacontentprovidervaluesparameter/UsingacontentproviderWHEREclause/Usingacontentprovider
update()method,SQLiteDatabase/BuildingtheUpdatequeryUPDATEcommand
about/Aquickreviewofdatabasefundamentalsupdatequery
building/BuildingtheUpdatequeryURI
about/UnderstandingcontentURIsUriinsert(Uriuri,ContentValuesvalues)method/Creatingacontentprovider
VVDBE
about/Thevirtualmachineversion,SQLite
about/SQLiteversionvirtualmachine
about/ThevirtualmachinevoidonCreate()method/Creatingacontentprovider
