ZetCode Android Tutorial

8/13/2019 ZetCode Android Tutorial

http://slidepdf.com/reader/full/zetcode-android-tutorial 1/77

ZetCode Android tutorial

This is Android development tutorial. The tutorial is suited for beginners. After reading this

tutorial, you will be able to program non-trivial Android applications.

Android

Android is a Linux based operating system designed for mobile devices such as smartphones

and tablet computers. It is also used for various networking euipments, smart T! systems,

wrist watches and household appliences. Applications for Android are developed in a

customi"ed version of the #ava programming language.

Introduction

This is an introductory Android development tutorial. The purpose of this tutorial is to get

you started with the develompent of applications in Android. The tutorial has been created

and tested on Linux.

Android

Android is a Linux based operating system designed for mobile devices such as smartphones

and tablet computers. It is also used for various networking euipment, smart T! systems,

wrist watches and household appliences. Applications for Android are developed in a

customi"ed version of the #ava programming language.

Android was developed in $%%& by a 'alifornian company which was later purchased by

(oogle. (oogle created the Android )pen *ource +roect for maintaining and developing of

the Android )*. Android is being developed uickly new versions of Android are freuently

being released. The Android code names are being choosed after some sweets, like onut,

(ingerbread or #elly /ean. evelopers can publish their applications in an online Android

market called Google Play. /efore an application is published on a (oogle +lay market, it

must be prepared for release, properly versioned and digitally signed. Android users use a

built-in application to search for applications on Android market and install them.

Android architecture

Android is based on a Linux kernel. The kernel is responsible for the device drivers,

memory management, process management and networking. Above the kernel, there are core

libraries and Android runtime. The libraries are '0'11 libraries that provide services such as

data storage, screen display, multimedia and web browsing. These capabilities are exposed

indirectly to developers through the Android application framework. The Android runtime

consists of the alvik virtual machine and the core #ava application libraries. alvik is a

virtual machine specifically developed to run #ava based applications on Android. It is

different from the standard #ava !irtual 2achine 3#!24. The next layer up is the application

framework . It is a set of A+Is to provide services to Android applications. It handles

application life cycle through Activity 2anager, notifications through 5otification manager,resources through 6esource 2anager, a set of graphical widgets 3called !iews in Android4,

7



package management trough +ackage 2anager and others. )n top of it sits the applications

layer. It is where our own applications are running. Android also has built-in applications

which can provide additional services to our applications. 8e can have access to browser,

*2*, calendars, maps or contacts.

Terms and concepts

Android application is an archive file with an .apk suffix. 9ach Android application lives on

its own in a security sandbox. An activity is a single screen with a user interface. An

application can have one or more activities. Activities are independent of each other.

Activities are subclasses of the Activity class. A service is an application component that

runs in the background. It does long running operations. It is a subclass of a *ervice class. A

content provider manages a shared set of application data. It is used to access : modify data

in the filesystem, *;Lite database or the web. It is a subclass of the 'ontent+rovider class. A

broadcast receiver is a component that receives broadcast notifications from the system or

applications. A broadcast receiver is implemented as a subclass of /roadcast6eceiver. 9ach

broadcast is delivered as an Intent obect. An intent is an asynchronous message. It is an

abstract description of an operation to be performed. Intents are used to navigate through

activities. Activities, services and broadcast receivers are activated through intents. A iew

class is a basic building block of a user interface. It is responsible for drawing and event

handling. A !iew is a base class for widgets, which are used to create <I components like

buttons or check boxes. A iewGroup is an obect that holds other !iew 3and !iew(roup4

obects in order to define the layout of the interface.

9ach Android application must have an AndroidManifest.xml file in the root directory. This

file presents essential information about the application to the Android system. The API level

is an integer value that uniuely identifies the framework A+I of the version of the Android platform. 9ach new Android platform brings new modifications to the Android application

framework. An !mulator is a virtual mobile device that runs on a computer. It is used to

develop and test Android applications without using a physical device. An Android irtual

"evice #A"$ is an emulator configuration that models an actual physical device such as

smartphone. 8e can create multiple A!s and test our applications on different hardware

platforms that use Android )*.

Installation

To start developing for Android, we need to download the Android *= 3*oftware

evelopment Toolkit4. There are two options. An 9clipse AT bundle or single *= tools.8e will go with the latter.

$ ls -sh android-sdk_r21-linux.tgz88M android-sdk_r21-linux.tgz

'urrently the file to dowload for Linux is android-sdk>r$7-linux.tg".

$ tar -xzvf android-sdk_r21-linux.tgz

8e uncompress the "ipped archive. The archive is extracted to the android-sdk-linux

directory.

$



$ pwd/home/an!odnar/!in/android-sdk-linux$ lsadd-ons platforms "# %eadme.txt tools

The Android *= archive initially contains only the basic *= tools. 8e need to dowload

additional tools with the *= manager. The Android *= manager is launched with theandroid command line tool.

?igure@ Android *= 2anager $ lsadd-ons platforms samples sour&es tempdo&s platform-tools "# %eadme.txt s'stem-images tools

These are the contents of the android-sdk-linux directory after installing additional tools.

export ()*+,$()*+/!in/android-sdk-linux/toolsexport ()*+,$()*+/!in/android-sdk-linux/platform-tools

8e add the tools and platform-tools directories to the +AT variable.

Android AVD

The Android A! 3Android !irtual evice4 is a is an emulator configuration that enables us

to model an actual device by defining hardware and software options to be emulated by the

Android 9mulator.

$ android avd

The command starts the Android !irtual evice 2anager.

?igure@ 'reating new A!

&



'licking on the 5ew button we start a dialog to create a new Android !irtual evice. In the

dialog we give the A! a name, select a hardware profile of the device, choose the A+I level

of the target or a dedicated storage area on our development machine.

$ android list avd

)vaila!le )ndroid irtual #evi&es 0ame )# (ath /home/an!odnar/.android/avd/)#.avd *arget )ndroid .2 3)(4 level 156 )74 armea!i-v5a "kin 2x8--------- 0ame )# (ath /home/an!odnar/.android/avd/)#.avd *arget )ndroid .2 3)(4 level 156 )74 armea!i-v5a "kin 2x2

The android list avd command shows all available Android !irtual evices.

Android Emulator

The Android emulator is a virtual mobile device that runs on our computer. It lets us develop

and test Android applications without using a physical device.

$ emulator -avd )#1 9

8e use the emulator command to start the emulator. 8e specify the name of the created

Android !irtual evice.

?igure@ 9mulator of a $.BC 3$D%x&$% ldpi4 device

D



The emulator is unlocked using the ?$ key. To list available applications, we click on the

circle icon. An application is uninstalled by clicking on the menu hardware button and

selecting 2anage apps option. Then we click on the icon of the application to uninstall and

click the <ninstall button.

This chapter was an introduction Android application development.

%irst Android application

In this chapter of the Android development tutorial we will create our first Android

application.

The application will ust display a message on the screen.

$ mkdir :irst

$ &d :irst/

8e create a ?irst directory and make it the current working directory.

$ android &reate proe&t --target android-15 --name :irst ;< --path . --a&tivit' Main)&tivit' --pa&kage &om.zet&ode.first=reated dire&tor'/home/an!odnar/programming/android/:irst/sr&/&om/zet&ode/first)dded file ./sr&/&om/zet&ode/first/Main)&tivit'.ava=reated dire&tor' /home/an!odnar/programming/android/:irst/res=reated dire&tor' /home/an!odnar/programming/android/:irst/!in...

8e create a new Android proect with the android &reate proe&t command. The target

option specifies the Android application framework version. The name option determines the

name of the proect. The path is the location of our proect directory. The activity is the name

of our default activity. ?inally, the package is the name of the package namespace for our

proect. The command creates a #ava file for the main activity, several directories and E2L

files.

$ ls)ndroidManifest.xml !in li!s proguard-proe&t.txt resant.properties !uild.xml lo&al.properties proe&t.properties sr&

These are the files and directories created by the android &reate proe&t command. The

AndroidManifest.xml file describes the fundamental characteristics of the application. The

source files of the application reside in the src directory. In the res directory, we have the

applicationFs resource files. The Android application archive file will be created in the bin

directory. The libs directory is used to store additional libraries. The ant.properties and

build.xml files are the Ant files used to build the proect. ?inally, the local.properties and the

project.properties are property files of the Android proect.

Android2anifest.xml>?xml version,@1.@ en&oding,@utf-8@?<>manifest xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ pa&kage,@&om.zet&ode.first@ androidversion=ode,@1@

G



androidversion0ame,@1.@< >appli&ation androidla!el,@Astring/app_name@ androidi&on,@Adrawa!le/i&_laun&her@< >a&tivit' androidname,@Main)&tivit'@ androidla!el,@Astring/app_name@< >intent-filter<

>a&tion androidname,@android.intent.a&tion.M)40@ /< >&ategor' androidname,@android.intent.&ategor'.B)C0=+D%@ /< >/intent-filter< >/a&tivit'< >/appli&ation<>/manifest<

This is the proect manifest file. It describes some basic characteristics of the Android proect.

The file provides the package name, which is com."etcode.com in our case. It contains the

name of the default activity. The @string/app_name and @drawable/ic_launcher are

resource values. The string resource values are set from the strings.xml file located in the

res0values subdirectory. The image resources are located in the drawable subdirectories of the

res directory. The <intent-filter> element of the main activity declares its capabilities. Itspecifies what the activity can do. The two intents specify that the activity is a main entry

point of the application, it can be the initial activity of a task and is listed in the top-level

application launcher.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<:irst program>/string< >string name,@messsage@<:irst )ndroid program>/string<>/resour&es<

In the strings.xml file we have one element which defines the resource value referenced from

the AndroidManifest.xml file. The file is located in the res0values subdirectory. 8e change

the value of the first element 3from F2ainActivityF to F?irst programF4. The name of the

application is shown in the list of the applications in the emulator. 8e add the second

element. It is referenced from the main.xml file.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@

androidla'out_height,@fill_parent@ <>*extiew androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@ androidtext,@Astring/message@ /<>/BinearBa'out<

This is the main.xml file located in the res0layout subdirectory. It defines the layout of an

Activity. The application loads the layout for an Activity in the on=reate36 method. In our

case we have a vertical linear layout with one Text!iew widget.

2ainActivity.ava

H



pa&kage &om.zet&ode.firstE

import android.app.)&tivit'Eimport android.os.7undleE

pu!li& &lass Main)&tivit' extends )&tivit'

F /GG =alled when the a&tivit' is first &reated. G/ AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E set=ontentiew3%.la'out.main6E II

This is the MainActivit.java source file. 8hen the activity is first created the on=reate36

method is called. The method loads the activity layout defined in the main.xml file.

Building the application

8e use the ant tool to build the Android application.

$ ant de!ug

8e execute the ant de!ug command in the proect root directory. There are two build

targets. ebug and release. 8e will use the debug build target. The release build needs some

additional work with signing.

$ ant de!ug install

It is possible to build and install the application in one step using the ant de!ug install

command.

$ ls -1 !in)ndroidManifest.xml)ndroidManifest.xml.d!uild.prop&lasses&lasses.dex&lasses.dex.d

:irst.ap_:irst.ap_.d:irst-de!ug.apk:irst-de!ug-unaligned.apk:irst-de!ug-unaligned.apk.darlist.&a&heproguard.txtres

The final Android package is created in the bin directory. The name of our archive file is

!irst-debug.ap" .

B



Running the application

8e install the application to the emulator and start it from it.

$ emulator -avd )#2 9

The emulator is started with a specific android virtual device.

$ ad! install !in/:irst-de!ug.apk

The ad! install command installs the application on the emulator.

?igure@ ?irst program

8e did not use a custom icon, so the built-in icon is used. ?rom the applications list we select

the ?irst program application. The application is launched.

?igure@ The ?irst program screen

8e can see the message that we have specified in the strings.xml file.

This chapter was an introduction Android application development.

&utton widgets

In this chapter of the Android development tutorial we will present button widgets.

A 7utton class represents a push button widget in Android. The full package path for the

button class is android.widgets./utton. /uttons are clicked to perform an action. A button can

display text or an icon. )r both. 9vent handlers for /utton click events are defined with the

android#on$lic" attribute of the /uttonJ element or programatically by setting the

set%n$lic"&istener'(iew.%n$lic"&istener).

Button

In the first example we define a button that closes an activity when pressed.

K



Android2anifest.xml>?xml version,@1.@ en&oding,@utf-8@?<>manifest xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ pa&kage,@&om.zet&ode.finish@ androidversion=ode,@1@ androidversion0ame,@1.@<

>appli&ation androidla!el,@Astring/app_name@androidi&on,@Adrawa!le/i&_laun&her@< >a&tivit' androidname,@Main)&tivit'@ androidla!el,@Astring/app_name@< >intent-filter< >a&tion androidname,@android.intent.a&tion.M)40@ /< >&ategor' androidname,@android.intent.&ategor'.B)C0=+D%@ /< >/intent-filter< >/a&tivit'< >/appli&ation<>/manifest<

This is the manifest file for the program.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ < >7utton androidla'out_height,@wrap_&ontent@ androidla'out_width,@wrap_&ontent@ androidla'out_margin*op,@1dip@

androidtext,@Astring/!tnla!el@ androidon=li&k,@on=li&k@ /<>/BinearBa'out<

In the main.xml layout file, we define one button widget with the /uttonJ element. The first

two attributes define the si"e of the button so that it is big enough to show its content. The

android#laout_margin*op+,dip, creates a margin between the title bar of the screen and

the button widget. The dip 3density independent pixel4 is a unit of measurement that is used

for Android layout management. It best reflects the rich diversity of resolutions and densities

of various Android appliances. The android#text+,@string/btnlabel, attribute defines a text

for the button. The actual text resides in the strings.xml file, which we cover before long.

?inally, the android#on$lic"+,on$lic", attribute creates a button event listener for the clickevent. All we need to do is to define the on'lick34 method in the relevant #ava source file.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<:inish !utton>/string< >string name,@!tnla!el@<:inish>/string<>/resour&es<

In the strings.xml file we have two resource strings. The first is used in the manifest file to

provide a name for the application and the main activity. The second is used in the layout file

to provide a text label for the button widget.



2ainActivity.avapa&kage &om.zet&ode.finishE

import android.app.)&tivit'Eimport android.view.iewEimport android.os.7undleE

pu!li& &lass Main)&tivit' extends )&tivit'F AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E set=ontentiew3%.la'out.main6E I

pu!li& void on=li&k3iew view6F

finish36E

II

This is the source file for the main activity. 8e have defined an on=li&k36 method which

reacts to the button click events. It must take a (iew as its sole parameter. The method calls

the finish36 method which closes the current activity. 8e are redirected back to the list of

applications.

?igure@ /utton

'licking on the button we are redirected back to the list of applications.

Showing a toast

A toast is a view that contains a uick message for the user. Toasts can be displayed for ashort or a long period of time. In our second application we create a button widget. It will

show a toast message after being pressed.

Android2anifest.xml>?xml version,@1.@ en&oding,@utf-8@?<>manifest xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ pa&kage,@&om.zet&ode.toast@ androidversion=ode,@1@ androidversion0ame,@1.@< >appli&ation androidla!el,@Astring/app_name@

androidi&on,@Adrawa!le/i&_laun&her@< >a&tivit' androidname,@Main)&tivit'@ androidla!el,@Astring/app_name@< >intent-filter<

7%



>a&tion androidname,@android.intent.a&tion.M)40@ /< >&ategor'androidname,@android.intent.&ategor'.B)C0=+D%@ /< >/intent-filter< >/a&tivit'< >/appli&ation<

>/manifest<

This is the manifest file.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ < >7utton

androidid,@AJid/!tn4d@ androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@ androidla'out_margin*op,@1dip@ androidtext,@Astring/la!el@ /<>/BinearBa'out<

In the main.xml layout file, we have one button widget inside the LinearLayout, which

arranges widgets in a single row or column. In our case the button is in a single column. The

button has a android#id+,@id/btn0d, attribute. The attribute supplies an identifier name for

the button. 8e will retrieve the button in the main activity using the findiew7'4d36

method. 8idgets that are not being referenced do not need this attribute. The plus sign is used

when we create the id of the element. *ubseuent references to the element in the E2L filewould be used without the plus sign. 3?or example in layout managers.4

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<"how *oast>/string< >string name,@la!el@<"how>/string<>/resour&es<

This is the strings.xml resource file. The button will have the F*howF text label.

2ainActivity.avapa&kage &om.zet&ode.toastE

import android.app.)&tivit'Eimport android.os.7undleEimport android.view.iewEimport android.view.iew.Hn=li&kBistenerEimport android.view.Kravit'Eimport android.widget.7uttonEimport android.widget.*oastEimport android.&ontent.=ontextE

pu!li& &lass Main)&tivit' extends )&tivit'F AHverride

77



pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E set=ontentiew3%.la'out.main6E

initC436E

I

pu!li& void initC436 F 7utton !tn , 37utton6 findiew7'4d3%.id.!tn4d6E

!tn.setHn=li&kBistener3new Hn=li&kBistener36F

AHverride pu!li& void on=li&k3iew arg6

F =ontext &tx , get)ppli&ation=ontext36E "tring msg , @7utton was &li&ked@E

int duration , *oast.BD0K*+_"+H%*E

*oast toast , *oast.make*ext3&txL msgL duration6E toast.setKravit'3Kravit'.=D0*D%L L 6E toast.show36E I I6E II

8hen we click on the button widget, it will show a Toast message in the center of the screen.

The toast will be displayed for a short period of time.

...import android.view.iew.Hn=li&kBistenerEimport android.view.Kravit'Eimport android.widget.7uttonEimport android.widget.*oastEimport android.&ontent.=ontextE

These are some of the new classes needed to be imported in this example.

initC436E

In the on=reate36 method we call the init<I34 method. It adds the Hn=li&kBistener36 tothe button widget.

7utton !tn , 37utton6 findiew7'4d3%.id.!tn4d6E

8e get the reference to the button widget that we have specified in the main.xml file. 8e use

the findiew7'4d36 method. The method finds a (iew 3A button is a kind of a !iew4 by the

id attribute from the main.xml file. The id is located in the auto-generated 6 class. 6 stands

for 6esource. 8e can have a look at the 6 source code in the gen0com0"etcode0toast06.ava

source file. There we will find the button id among others.

!tn.setHn=li&kBistener3new Hn=li&kBistener36F AHverride

7$



pu!li& void on=li&k3iew arg6F

... II6E

8e add the Hn=li&kBistener to the button widged. Listeners can be set up in various ways.ere we use an anonymous inner class.

=ontext &tx , get)ppli&ation=ontext36E"tring msg , @7utton was &li&ked@Eint duration , *oast.BD0K*+_"+H%*E

*oast toast , *oast.make*ext3&txL msgL duration6Etoast.setKravit'3Kravit'.=D0*D%L L 6Etoast.show36E

8e set up and show the Toast view. 8e get the application context, create a message and the

duration time. The gravity is the alignment of the view within its parent. 8e position the toastin the center of the screen. /y default, the toasts are displayed at the bottom of the screen.

?igure@ *howing toast

CheckBox

A 'heck/ox widget is a special kind of a button. It has two states. )n and off. The on state is

represented by a tick mark inside a rectangle.

ava.lang.H!e&t android.view.iew android.widget.*extiew android.widget.7utton android.widget.=ompound7utton android.widget.=he&k7ox

This is the inheritance hierarchy for the 'heck/ox widget. The /utton widget is among its

parents.

7&



Android2anifest.xml>?xml version,@1.@ en&oding,@utf-8@?<>manifest xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ pa&kage,@&om.zet&ode.&he&k!ox@ androidversion=ode,@1@ androidversion0ame,@1.@<

>appli&ation androidla!el,@Astring/app_name@androidi&on,@Adrawa!le/i&_laun&her@<

>a&tivit' androidname,@Main)&tivit'@ androidla!el,@Astring/app_name@< >intent-filter< >a&tion androidname,@android.intent.a&tion.M)40@ /< >&ategor'androidname,@android.intent.&ategor'.B)C0=+D%@ /< >/intent-filter< >/a&tivit'< >/appli&ation<>/manifest<

The manifest file.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ < >=he&k7ox androidid,@AJid/&!_id@ androidla'out_width,@wrap_&ontent@

androidla'out_height,@wrap_&ontent@ androidtext,@Astring/&!la!el@ /<>/BinearBa'out<

The 'heck/oxJ element creates a 'heck/ox widget.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<=he&k7ox>/string< >string name,@&!la!el@<"how title>/string<>/resour&es<

*tring resources.

2ainActivity.avapa&kage &om.zet&ode.&he&k!oxE

import android.app.)&tivit'Eimport android.os.7undleEimport android.view.iewEimport android.view.iew.Hn=li&kBistenerEimport android.widget.=he&k7oxE

pu!li& &lass Main)&tivit' extends )&tivit'F private =he&k7ox &!E

7D



AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E set=ontentiew3%.la'out.main6E

initC436E I

pu!li& void initC436F

&! , 3=he&k7ox6 findiew7'4d3%.id.&!_id6E &!.set=he&ked3true6E

&!.setHn=li&kBistener3new Hn=li&kBistener36F

AHverride pu!li& void on=li&k3iew v6

F =he&k7ox &! , 3=he&k7ox6 vE

if 3&!.is=he&ked366F

set*itle3@=he&k7ox@6E I else F set*itle3@@6E I I I6E II

The 'heck/ox toggles the visibility of the screen title. 8hen the 'heck/ox is in a checked

state, the title is visible. )thervise it is not.

import android.widget.=he&k7oxE

8e import the 'heck/ox class into the source file.

&! , 3=he&k7ox6 findiew7'4d3%.id.&!_id6E

8e find the reference to the 'heck/ox widget, defined in the main.xml file.

&!.set=he&ked3true6E

The title is visible by default, so the 'heck/ox must be in a checked state. 8e use the

set=he&ked36 method to change the state of the widget.

&!.setHn=li&kBistener3new Hn=li&kBistener36F AHverride pu!li& void on=li&k3iew v6

F=he&k7ox &! , 3=he&k7ox6 vE

if 3&!.is=he&ked366F

7G



set*itle3@=he&k7ox@6E I else F set*itle3@@6E I II6E

In the Hn=li&kBistener36 we define the on=li&k36 method. 8e determine the state of the

widget using the is=he&ked36 method. The title of the screen is modified with the

set*itle36 method.

?igure@ 'heck/ox widget

In this chapter of the Android development tutorial we have presented button widgets.

Intents

In this chapter of the Android development tutorial, we will talk about Intents.

According to the Android developer documentation, an 0ntent is an asynchronous message. It

is an abstract description of an operation to be performed. Intents are used to navigate

through activities. Activities, services and broadcast receivers are activated through intents.Intents enable loose coupling of code in the application. An Intent is passed to the some

method like =ontext.start)&tivit'36 or =ontext.start"ervi&e36 to perform some

action.

There are two types of intents. 9xplicit and implicit. In explicit intents you provide the name

of the Activity class. In implicit intents, you tell the system what to do rather than name the

Activity class to launch.

Implicit Intent

isplaying a web page can be done via an implicit intent. It will start a default web browser

with the specified web page. In the example we will display the contents of a web page. The

manifest file is not modified.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ androidorientation,@verti&al@ <

>7utton androidid,@AJid/!utton1@ androidla'out_width,@wrap_&ontent@

7H



androidla'out_height,@wrap_&ontent@ androidla'out_margin,@dp@ androidon=li&k,@on=li&ked@ androidtext,@Astring/!tn_title@ /< >/BinearBa'out<

In the main.xml layout file, we have ust a simple button widget. 'licking on the button will

show the web page.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<Crl>/string< >string name,@!tn_title@<isit>/string<>/resour&es<

*tring resources.

2ainActivity.avapa&kage &om.zet&ode.urlE

import android.app.)&tivit'Eimport android.os.7undleEimport android.&ontent.4ntentEimport android.net.CriEimport android.view.iewE

pu!li& &lass Main)&tivit' extends )&tivit'F

AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E set=ontentiew3%.la'out.main6E I

pu!li& void on=li&ked3iew view6 F 4ntent intent , new 4ntent34ntent.)=*4H0_4DNL

Cri.parse3@http//www.google.&om@66E start)&tivit'3intent6E

II

This is the 2ainActivity.ava source file.

pu!li& void on=li&ked3iew view6F 4ntent intent , new 4ntent34ntent.)=*4H0_4DNL

Cri.parse3@http//www.google.&om@66E start)&tivit'3intent6EI

In the on=li&ked36 method, we create an Intent obect and start a new activity. 8ith this

implicit intent, we tell Android to start a default web browser with google.com web pageopened.

7B



?igure@ 8eb page in Android emulator

Explicit intent In explicit intents, we provide the exact class to be run.

Android2anifest.xml>?xml version,@1.@ en&oding,@utf-8@?<>manifest xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ pa&kage,@&om.zet&ode.expli&it@ androidversion=ode,@1@ androidversion0ame,@1.@< >appli&ation androidla!el,@Astring/app_name@

androidi&on,@Adrawa!le/i&_laun&her@< >a&tivit' androidname,@Main)&tivit'@ androidla!el,@Astring/app_name@< >intent-filter< >a&tion androidname,@android.intent.a&tion.M)40@ /< >&ategor'androidname,@android.intent.&ategor'.B)C0=+D%@ /< >/intent-filter< >/a&tivit'<

>a&tivit' androidname,@.0ext)&tivit'@<>/a&tivit'<

>/appli&ation<>/manifest<

In the manifest file we register the new activity under the name 5extActivity. The leading dot

is a shorthand for the full package name, com."etcode.explicit in our case.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ < >7utton androidid,@AJid/!utton1@ androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@

7K



androidla'out_margin,@dp@ androidon=li&k,@on=li&ked@ androidtext,@Astring/!tn_title@ /<>/BinearBa'out<

In the main.xml file we have one button. 'licking on this button will start a new explicit

activity.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<Dxpli&it>/string< >string name,@!tn_title@<0ext>/string<>/resour&es<

This is the strings.xml resource file.

$ ls sr&/&om/zet&ode/expli&it/Main)&tivit'.ava 0ext)&tivit'.ava

In the src0com0"etcode0explicit subdirectory we have two source files for two activities.

2ainActivity.avapa&kage &om.zet&ode.expli&itE

import android.app.)&tivit'Eimport android.os.7undleEimport android.view.iewEimport android.&ontent.4ntentE

pu!li& &lass Main)&tivit' extends )&tivit'F AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E set=ontentiew3%.la'out.main6E I

pu!li& void on=li&ked3iew view6 F 4ntent intent , new 4ntent3thisL 0ext)&tivit'.&lass6E start)&tivit'3intent6E

II

This is the source for the main activity. In the on'licked34 method, we start a new explicit

intent.

pu!li& void on=li&ked3iew view6F 4ntent intent , new 4ntent3thisL 0ext)&tivit'.&lass6E start)&tivit'3intent6EI

The second parameter of the Intent constructor is the class name to be invoked. The activityis started with the start)&tivit'36 method.

7



5extActivity.avapa&kage &om.zet&ode.expli&itE

import android.app.)&tivit'Eimport android.os.7undleEimport android.widget.*extiewE

import android.widget.BinearBa'outE

pu!li& &lass 0ext)&tivit' extends )&tivit'F AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E initC436E I

pu!li& void initC436 F

BinearBa'out la' , new BinearBa'out3this6E

*extiew tv , new *extiew3this6E tv.set*ext3@0ext s&reen@6E la'.addiew3tv6E

set=ontentiew3la'6E II

This is the 1extActivit.java source code. In this activity, we show a Text!iew on the screen.

It is programatically placed into a linear layout.

Transfering data

Intents are used to transfer data from one activity to another. 8e use the putDxtra36 method

to add extra data to an intent. In the following example, we write a name to the edit text and

click on the *end button. 8e will land on another screen where we will see a greeting to the

name, that we have entered.

$ ls res/la'out/s&reen1.xml s&reen2.xml$ ls sr&/&om/zet&ode/swit&h2/:irst"&reen.ava "e&ond"&reen.ava

In the res0layout directory we have two E2L layout files. In the src0com0"etcode0switch$ we

have source files of two activities.

Android2anifest.xml>?xml version,@1.@ en&oding,@utf-8@?<>manifest xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ pa&kage,@&om.zet&ode.swit&h2@ androidversion=ode,@1@ androidversion0ame,@1.@< >appli&ation androidla!el,@Astring/app_name@ androidi&on,@Adrawa!le/i&_laun&her@< >a&tivit' androidname,@.:irst"&reen@< >intent-filter<

$%



>a&tion androidname,@android.intent.a&tion.M)40@ /< >&ategor'androidname,@android.intent.&ategor'.B)C0=+D%@ /< >/intent-filter< >/a&tivit'<

>a&tivit' androidname,@."e&ond"&reen@<>/a&tivit'< >/appli&ation<

>/manifest<

In the manifest file we define two activities. The ?irst*creen and the *econd*creen activity.

The ?irst*creen is the main activity.

screen7.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@

androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ < >Ddit*ext androidid,@AJid/edit4d@ androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@ androidla'out_margin*op,@1dip@ androidla'out_margin7ottom,@1dip@ androidhint,@Astring/et+int@ /<

>7utton androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@

androidtext,@Astring/!tn_send@androidon=li&k,@sendMessage@ /<>/BinearBa'out<

The screen.xml layout file is loaded by the ?irst*creen activity. It displays an 9ditText and a

/utton widget. The android@hint attribute shows a default shaded text in the 9ditText.

screen$.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@

androidla'out_height,@fill_parent@ < >*extiew androidid,@AJid/tv4d@ androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@ /<>/BinearBa'out<

In the screen2.xml file we have one Text!iew widget. It will display the text that we will

transfer from one screen to another. It is loaded by the *econd*creen activity.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es<

$7



>string name,@app_name@<"wit&h>/string< >string name,@et+int@<Dnter 'our name>/string< >string name,@!tn_send@<"end>/string<>/resour&es<


?irst*creen.avapa&kage &om.zet&ode.swit&h2E

import android.app.)&tivit'Eimport android.os.7undleEimport android.&ontent.4ntentEimport android.view.iewEimport android.widget.Ddit*extE

pu!li& &lass :irst"&reen extends )&tivit'F

private Ddit*ext inameE AHverride

pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E

set*itle3@:irst s&reen@6E set=ontentiew3%.la'out.s&reen16E

iname , 3Ddit*ext6 findiew7'4d3%.id.edit4d6E I

pu!li& void sendMessage3iew view6F

4ntent swit&h*o , new 4ntent3thisL "e&ond"&reen.&lass6Eswit&h*o.putDxtra3@name@L iname.get*ext36.to"tring366Estart)&tivit'3swit&h*o6E

II

The ?irst*creen is the main activity. The sendMessage36 method is called, when we click on

the button.

pu!li& void sendMessage3iew view6F 4ntent swit&h*o , new 4ntent3thisL "e&ond"&reen.&lass6E

swit&h*o.putDxtra3@name@L iname.get*ext36.to"tring366Estart)&tivit'3swit&h*o6E

I

In the sendMessage36 method, we create an instance of an Intent. It will direct us to the

*econd*creen activity. 8ith the putDxtra36 method, we add data from the 9ditText to the

intent. The first parameter is the name by which we will refer the data. The second parameter

is the data to be transfered.

*econd*creen.ava

pa&kage &om.zet&ode.swit&h2E

import android.app.)&tivit'E

$$



import android.os.7undleEimport android.&ontent.4ntentEimport android.widget.*extiewE

pu!li& &lass "e&ond"&reen extends )&tivit'F

AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E set=ontentiew3%.la'out.s&reen26E

setupC436E I

void setupC436 F set*itle3@"e&ond s&reen@6E

*extiew tv , 3*extiew6 findiew7'4d3%.id.tv4d6E 4ntent i , get4ntent36E

"tring name , i.get"tringDxtra3@[email protected]*ext3@Oou have entered @ J name6E

II

This is the *econd*creen.ava source file. It is called by the ?irst*creen activity.

setupC436E

In the setup<I34 method, we set up the user interface of the screen.

set*itle3@"e&ond s&reen@6E

8e give the title to the screen with the set*itle36 method.

4ntent i , get4ntent36E"tring name , i.get"tringDxtra3@[email protected]*ext3@Oou have entered @ J name6E

The get4ntent36 method returns the intent that started the activity. 8e get the extra data

using the get"tringDxtra36 method. The data is set to the Text!iew.

In this chapter of the Android development tutorial, we have written about Intents.

Layout management

In this chapter of the Android development tutorial we will talk about layout management.

widgets.

8hen we design the user interface of our application, we decide what components we will

use and how we will organi"e those components in the application. To organi"e ourcomponents, we use speciali"ed non visible obects called layout managers.

$&



There are several layout managers in Android. A &inear&aout lines up its views in one row

or column. A !rame&aout is a simple layout manager used to display one view. A

3elative&aout is a layout manager in which the views are positioned in relation to each other

or to the parent. The most powerful layout manager is the 4rid&aout manager. It arranges

the views in a grid.

Showing an image with rame!a"out

The first example shows an image using the ?rameLayout manager.

$ ls res/drawa!le-hdpi/i&_laun&her.png zamok.pg

epending on a android virtual device we are using, we put the image in the corresponding

subdirectory of the res directory.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>:rameBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidla'out_gravit',@top@ androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@ < >4mageiew

androidla'out_height,@mat&h_parent@androidla'out_width,@mat&h_parent@androidsr&,@Adrawa!le/zamok@ /<

>/:rameBa'out<

In the ?rameLayout manager, we put one Image!iew.

>:rameBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidla'out_gravit',@top@ androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@ <

The :rameBa'out is big enough to display the 4mageiew by setting the layout width and

height to wrap_&ontent. It is pushed to the top using the la'out_gravit' attribute.

>4mageiewandroidla'out_height,@mat&h_parent@androidla'out_width,@mat&h_parent@androidsr&,@Adrawa!le/zamok@ /<

The 4mageiew displays an image. The image is located in a subdirectory of the res directory.

$D



?igure@ *howing an image with a ?rameLayout

A row of #uttons

In the example we create a row of four buttons.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@horizontal@ androidla'out_width,@mat&h_parent@

androidla'out_height,@mat&h_parent@ < >7utton

androidla'out_height,@wrap_&ontent@ androidla'out_width,@wrap_&ontent@ androidtext,@7utton1@ /<

>7utton androidla'out_height,@wrap_&ontent@ androidla'out_width,@wrap_&ontent@ androidtext,@7utton2@ /<

>7utton androidla'out_height,@wrap_&ontent@ androidla'out_width,@wrap_&ontent@ androidtext,@7utton@ /< >7utton

androidla'out_height,@wrap_&ontent@ androidla'out_width,@wrap_&ontent@ androidtext,@7utton@ /<

>/BinearBa'out<

8e have a hori"ontal BinearBa'out. In this layout, we add four buttons.

>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@

$G



androidorientation,@horizontal@ androidla'out_width,@mat&h_parent@ androidla'out_height,@mat&h_parent@ <

8e create a hori"ontal LinearLayout manager. The width and height of the layout match the

parent which means that it fills the entire screen.

>7utton androidla'out_height,@wrap_&ontent@ androidla'out_width,@wrap_&ontent@ androidtext,@7utton1@ /<

9ach of the four buttons use the wrap>content property. They are then ust big enough to

display their content.

?igure@ A row of buttons

A row of #uttons II

In the third example of this chapter, we show how to programatically create a row of buttonswith a LinearLayout manager.

2ainActivity.avapa&kage &om.zet&ode.!tnrow2E

import android.app.)&tivit'Eimport android.os.7undleEimport android.widget.7uttonEimport android.widget.BinearBa'outE

pu!li& &lass 7utton%ow2 extends )&tivit'F

AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E

initC436E I

pu!li& void initC436 F 7utton !tn1 , new 7utton3this6E !tn1.set*ext3@7utton@6E

7utton !tn2 , new 7utton3this6E !tn2.set*ext3@7utton@6E

$H



7utton !tn , new 7utton3this6E !tn.set*ext3@7utton@6E

7utton !tn , new 7utton3this6E !tn.set*ext3@7utton@6E

BinearBa'out ll , new BinearBa'out3this6E ll.setHrientation3BinearBa'out.+H%4PH0*)B6E

ll.addiew3!tn16E ll.addiew3!tn26E ll.addiew3!tn6E ll.addiew3!tn6E

set=ontentiew3ll6E II

?our buttons are placed in a hori"ontal LinearLayout. 8e will not use the layout E2L file inthis sample.

7utton !tn1 , new 7utton3this6E!tn1.set*ext3@7utton@6E

A 7utton widget is created. The text is set for the button with the set*ext36 method.

BinearBa'out ll , new BinearBa'out3this6Ell.setHrientation3BinearBa'out.+H%4PH0*)B6E

A hori"ontal BinearBa'out is created.

ll.addiew3!tn16Ell.addiew3!tn26Ell.addiew3!tn6Ell.addiew3!tn6E

/uttons are added to the layout manager.

set=ontentiew3ll6E

The linear layout manager is set to be the content view of the activity.

A column of #uttons

8e use the ?rameLayout and the LinearLayout managers to create a column of buttons

centered on the screen.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>:rameBa'out

xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@androidla'out_width,@wrap_&ontent@

androidla'out_height,@wrap_&ontent@ androidla'out_gravit',@&enter@<

$B



>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@

androidorientation,@verti&al@ androidla'out_width,@mat&h_parent@ androidla'out_height,@mat&h_parent@ <

>7utton androidla'out_height,@wrap_&ontent@ androidla'out_width,@wrap_&ontent@

androidtext,@7utton@ /<



>7utton androidla'out_height,@wrap_&ontent@

androidla'out_width,@wrap_&ontent@androidtext,@7utton@ /<



>/BinearBa'out<

>/:rameBa'out<

A LinearLayout manager with four buttons is placed in the ?rameLayout manager.

>:rameBa'outxmlnsandroid,@http//s&hemas.android.&om/apk/res/android@androidla'out_width,@wrap_&ontent@androidla'out_height,@wrap_&ontent@

androidla'out_gravit',@&enter@<

The ?rameLayout does not occupy all the available space. It is ust big enough to take all the

four buttons. And therefore we can use the la'out_gravit' attribute to center the

LinearLayout and its four buttons.

>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@mat&h_parent@ androidla'out_height,@mat&h_parent@ <

A vertical LinearLayout is created.

$K



?igure@ A column of buttons

Relati$e!a"out

6elativeLayout lets child views specify their position relative to the parent view or to each

other. The views are referenced by their ids.

main.xml

>?xml version,@1.@ en&oding,@utf-8@?<>%elativeBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ <

>Ddit*ext androidid,@AJid/et4d@ androidla'out_margin*op,@1dp@

androidla'out_width,@mat&h_parent@ androidla'out_height,@wrap_&ontent@ /<

>7utton

androidid,@AJid/!tn_send4d@ androidla'out_!elow,@AJid/et4d@ androidla'out_width,@wrap_&ontent@

androidla'out_height,@wrap_&ontent@androidtext,@"end@ /<

>7utton androidid,@AJid/!tn_&lear4d@ androidla'out_!elow,@AJid/et4d@ androidla'out_to%ightHf,@AJid/!tn_send4d@ androidla'out_width,@wrap_&ontent@

androidla'out_height,@wrap_&ontent@androidtext,@=lear@ /<

>/%elativeBa'out<

$



The E2L code displays an 9ditText with two buttons.

>Ddit*ext androidid,@AJid/et4d@ androidla'out_margin*op,@1dp@

androidla'out_width,@mat&h_parent@

androidla'out_height,@wrap_&ontent@ /<

The Ddit*ext will be stretched from right to left by setting the androidla'out_width to

androidmat&h_parent . The widget will be high enough to show its contents. 8e specify

some gap between the widget and the border of the screen with androidla'out_margin*op

property.

>7utton androidid,@AJid/!tn_send4d@ androidla'out_!elow,@AJid/et4d@ androidla'out_width,@wrap_&ontent@

androidla'out_height,@wrap_&ontent@androidtext,@"end@ /<

The *end button widget will be placed below the 9ditText widget. To accomplish this, we

use the androidla'out_!elow property. 5ote that we reference the id of the widget that we

relate to.

>7utton androidid,@AJid/!tn_&lear4d@ androidla'out_!elow,@AJid/et4d@ androidla'out_to%ightHf,@AJid/!tn_send4d@ androidla'out_width,@wrap_&ontent@

androidla'out_height,@wrap_&ontent@androidtext,@=lear@ /<

The 'lear button is placed below the 9ditText widget and to the right of the *end button. 8e

accomplish this by two properties. The androidla'out_!elow and the

androidla'out_to%ightHf property.

?igure@ 6elativeLayout example

&%



%rid

A 4rid&aout manager places its children in a rectangular grid. The grid consists of row and

columns. The intersections of rows and columns are cells. 9ach cell is referenced by its

index. A view in a grid can occupy one or more cells. The gravit is a property that specifies

how a view should be placed in its group of cells.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>KridBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidla'out_width,@mat&h_parent@

androidla'out_height,@mat&h_parent@ <

>7utton androidtext,@3L 6@

androidla'out_row,@@

androidla'out_&olumn,@@ /<

>7utton androidla'out_row,@@

androidla'out_&olumn,@1@androidla'out_&olumn"pan,@2@

androidla'out_gravit',@fill_horizontal@ /<


androidla'out_row,@@androidla'out_&olumn,@@ /<

>7utton androidtext,@3L 6@androidla'out_row,@@androidla'out_&olumn,@@ /<

>7uttonandroidla'out_row,@1@

androidla'out_&olumn,@@ androidla'out_row"pan,@@

androidla'out_&olumn"pan,@@androidla'out_gravit',@fill@ /<

>7utton androidtext,@=enter@

androidla'out_row,@@ androidla'out_&olumn,@@ androidla'out_&olumn"pan,@@

androidla'out_gravit',@&enter_horizontal@ /<

>7utton androidtext,@%ight@


androidla'out_gravit',@right@ /<

>/KridBa'out<

&7



In the example we put a few buttons in a (ridLayout. 8e show how a button can stretch over

several cells.


androidla'out_row,@@androidla'out_&olumn,@@ /<

<sing the la'out_row and la'out_&olumn properties, we place a button at top-left cell. The

indeces start from "ero.

>7utton androidla'out_row,@@

androidla'out_&olumn,@1@androidla'out_&olumn"pan,@2@

androidla'out_gravit',@fill_horizontal@ /<

This button will span two columns. The la'out_gravit' property will cause the button tofill the two columns.

>7uttonandroidla'out_row,@1@

androidla'out_&olumn,@@ androidla'out_row"pan,@@

androidla'out_&olumn"pan,@@androidla'out_gravit',@fill@ /<

This button will span three rows and five columns.

>7utton androidtext,@=enter@


androidla'out_gravit',@&enter_horizontal@ /<

A view may not occupy all the space that was allotted to it. This button is hori"ontally

centered within five columns.

&$



?igure@ (ridLayout example

In this chapter of the Android development tutorial we worked with layout management.

'pinner widget

In this chapter of the Android development tutorial we will present a spinner widget.

A spinner widget enables a user to select an item from a list of options. In the normal state itshows the currently selected item. 'licking on the spinner widget shows a dropdown menu

with all available items. The user can choose a new one from the list. The "pinner class is

used to create a spinner widget.

The *pinner widget can be populated in the E2L file. )r it can be programatically filled. In

the latter case we need an Adapter class to populate the *pinner widget. An adapter is a

bridge between a *pinner and its data.

Spinner I

In the first example we have a *pinner widget whose items are defined in an E2L file.

Android2anifest.xml>?xml version,@1.@ en&oding,@utf-8@?<>manifest xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ pa&kage,@&om.zet&ode.finish@ androidversion=ode,@1@ androidversion0ame,@1.@< >appli&ation androidla!el,@Astring/app_name@androidi&on,@Adrawa!le/i&_laun&her@< >a&tivit' androidname,@Main)&tivit'@ androidla!el,@Astring/app_name@<

>intent-filter< >a&tion androidname,@android.intent.a&tion.M)40@ /<

&&



>&ategor' androidname,@android.intent.&ategor'.B)C0=+D%@ /< >/intent-filter< >/a&tivit'< >/appli&ation<>/manifest<

This is the manifest file for the program.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ < >"pinner androidid,@AJid/spn@ androidla'out_width,@wrap_&ontent@

androidla'out_height,@wrap_&ontent@ androidentries,@Aarra'/dlangs@ androidla'out_margin*op,@1dip@ androidprompt,@Astring/spn_title@ /<

>*extiew androidid,@AJid/tv4d@ androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@

androidla'out_margin*op,@1dip@ /<

>/BinearBa'out<

In the main.xml layout file, we have a *pinner and a Text!iew. The

android#entries+,@arra/dlangs, attribute defines a E2L resource that provides an array of

strings. The strings are written in the strings.xml file.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<"pinner>/string< >string name,@spn_title@<=hoose a language>/string<

>string-arra' name,@dlangs@<

>item<('thon>/item< >item<(+(>/item< >item<(erl>/item< >item<*&l>/item< >item<%u!'>/item< >/string-arra'<

>/resour&es<

In the strings.xml file we have the elements of the string array. These are displayed when we

click on the *pinner widget.

2ainActivity.avapa&kage &om.zet&ode.spinnerE

&D



import android.app.)&tivit'Eimport android.os.7undleEimport android.view.iewEimport android.widget.*extiewEimport android.widget."pinnerEimport android.widget.)dapteriewE

import android.widget.)dapteriew.Hn4tem"ele&tedBistenerE

pu!li& &lass Main)&tivit' extends )&tivit' implementsHn4tem"ele&tedBistenerF private *extiew tvE


tv , 3*extiew6 findiew7'4d3%.id.tv4d6E

"pinner spn , 3"pinner6 findiew7'4d3%.id.spn6E spn.setHn4tem"ele&tedBistener3this6E I

AHverride pu!li& void on4tem"ele&ted3)dapteriew>?< parentL iew vL int posL longid6

F "tring item , parent.get4tem)t(osition3pos6.to"tring36E tv.set*ext3item6E

I

AHverride pu!li& void on0othing"ele&ted3)dapteriew>?< arg6

Ftv.set*ext3@@6E

II

The selected item from the *pinner widget is displayed in the Text!iew widget.

pu!li& &lass Main)&tivit' extends )&tivit' implementsHn4tem"ele&tedBistener

The 2ainActivity class implements the Hn4tem"ele&tedBistener . The class must now

implement two methods. The on4tem"ele&ted36 and on0othing"ele&ted36 methods.

"pinner spn , 3"pinner6 findiew7'4d3%.id.spn6Espn.setHn4tem"ele&tedBistener3this6E

These two lines get the reference to the *pinner widget and set the )nItem*electedListener

for it.

AHverride

pu!li& void on4tem"ele&ted3)dapteriew>?< parentL iew vL int posL long id6F

&G



"tring item , parent.get4tem)t(osition3pos6.to"tring36E tv.set*ext3item6EI

In the on4tem"ele&ted36 method we get the currently selected *pinner item with the

get4tem)t(osition36. The item is transformed to a string and set to the Text!iew.

?igure@ *pinner widget

Spinner II

In the second spinner example, we will define our list of spinner elements programatically.

?or this we will use the )rra')dapter in conunction with the )rra'Bist.

An Adapter design pattern is used by Android platform to work with the *pinner widget. The

)rra')dapter is an intermediary between the data source and the data view. In this case the

data source is the ArrayList and the view is the *pinner widget. <sing an adapter we are

decoupling our code.

Android2anifest.xml>?xml version,@1.@ en&oding,@utf-8@?<>manifest xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ pa&kage,@&om.zet&ode.toast@ androidversion=ode,@1@ androidversion0ame,@1.@< >appli&ation androidla!el,@Astring/app_name@

androidi&on,@Adrawa!le/i&_laun&her@< >a&tivit' androidname,@Main)&tivit'@ androidla!el,@Astring/app_name@< >intent-filter<

>a&tion androidname,@android.intent.a&tion.M)40@ /< >&ategor'androidname,@android.intent.&ategor'.B)C0=+D%@ /< >/intent-filter< >/a&tivit'< >/appli&ation<>/manifest<

This is the manifest file.


&H



androidla'out_height,@fill_parent@ < >"pinner

androidid,@AJid/spn4d@ androidla'out_width,@wrap_&ontent@

androidla'out_height,@wrap_&ontent@ androidla'out_margin*op,@1dip@androidprompt,@Astring/spn_title@ /<

>*extiew androidid,@AJid/tv4d@ androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@ androidla'out_margin*op,@1dip@ /< >/BinearBa'out<

In the main.xml file we have two widgets. The *pinner and the Text!iew widget. This time

we do not define the array data entries for the *pinner.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<"pinner2>/string< >string name,@spn_title@<=hoose a language>/string<>/resour&es<


2ainActivity.avapa&kage &om.zet&ode.spinner2E

import ava.util.)rra'BistEimport ava.util.BistE

import android.app.)&tivit'Eimport android.os.7undleEimport android.view.iewEimport android.widget."pinnerEimport android.widget.)rra')dapterEimport android.widget.*extiewEimport android.widget.)dapteriewEimport android.widget.)dapteriew.Hn4tem"ele&tedBistenerE

pu!li& &lass Main)&tivit' extends )&tivit' implementsHn4tem"ele&tedBistenerF private *extiew tvE private "pinner spnE


setup36E

&B



I

pu!li& void setup36 F tv , 3*extiew6 findiew7'4d3%.id.tv4d6E

spn , 3"pinner6 findiew7'4d3%.id.spn4d6E fill"pinner3spn6E spn.setHn4tem"ele&tedBistener3this6E I

pu!li& void fill"pinner3"pinner spn6F

Bist>"tring< lst , new )rra'Bist>"tring<36E lst.add3@('thon@6E lst.add3@(+(@6E lst.add3@(erl@6E lst.add3@*&l@6E lst.add3@%u!'@6E

)rra')dapter>"tring< da , new )rra')dapter>"tring<3thisL android.%.la'out.simple_spinner_itemL lst6E da.set#rop#owniew%esour&e3android.%.la'out.simple_spinner_item6E

spn.set)dapter3da6E I

AHverride pu!li& void on4tem"ele&ted3)dapteriew>?< parentL iew vL int posL longid6

F "tring item , parent.get4tem)t(osition3pos6.to"tring36E

tv.set*ext3item6E I

AHverride pu!li& void on0othing"ele&ted3)dapteriew>?< arg6

Ftv.set*ext3@@6E

II

In the 2ainActivity.ava source file we fill the *pinner widget with data and implement the

)nItem*electedListener for the widget.

spn , 3"pinner6 findiew7'4d3%.id.spn4d6Efill"pinner3spn6E

8e get the reference to the "pinner widget and call the fill*pinner34 method to populate it

with data.

Bist>"tring< lst , new )rra'Bist>"tring<36Elst.add3@('[email protected]@(+(@6Elst.add3@([email protected]@*&[email protected]@%u!'@6E

An )rra'Bist is created and filled with strings.

&K



)rra')dapter>"tring< da , new )rra')dapter>"tring<3thisL android.%.la'out.simple_spinner_itemL lst6E

The instance of the )rra')dapter is created. It takes the ArrayList as a parameter.

da.set#rop#owniew%esour&e3android.%.la'out.simple_spinner_item6E

This line determines the look of the dropdown menu of the *pinner widget. This one is a

dropdown without radio buttons. A spinner with the

android.%.la'out.simple_spinner_dropdown_item defined has radio buttons in its rows.

spn.set)dapter3da6E

The adapter is set for the *pinner widget.

?igure@ *pinner dropdown menu

In this chapter of the Android development tutorial, we have written about a spinner widget.

'eek&ar widget

In this chapter of the Android development tutorial we will present the *eek/ar widget.

The *eek/ar widget is used to select a value from a range of values. The user drags a thumb

of the widget to select a specific value. To process the *eek/ar events, we implement the

5ee"6ar.%n5ee"6ar$hange&istener listener.

&



SeekBar example

8e have a *eek/ar widget and a Text!iew widget. The current value from the *eek/ar is

displayed in the Text!iew. Android manifest file is left untouched.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ <>"eek7ar androidid,@AJid/s!4d@ androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@ androidla'out_margin,@1dp@ androidmax,@1@

androidprogress,@@ /<>*extiew androidid,@AJid/tv4d@ androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@ androidla'out_marginBeft,@1dp@ /<>/BinearBa'out<

In the main.xml layout file, we have two widgets defined. The *eek/ar widget and the

Text!iew widget.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<"eek7ar>/string< >string name,@init_tv_value@<>/string<>/resour&es<

This is strings.xml resource file. The init>tv>value is the initial value of the Text!iew widget.

2ainActivity.avapa&kage &om.zet&ode.seek!arE

import android.app.)&tivit'Eimport android.os.7undleEimport android.widget.*extiewEimport android.widget."eek7arEimport android.widget."eek7ar.Hn"eek7ar=hangeBistenerE

pu!li& &lass Main)&tivit' extends )&tivit' implementsHn"eek7ar=hangeBistener

F *extiew tvE

AHverride

pu!li& void on=reate37undle saved4nstan&e"tate6 F

D%



super.on=reate3saved4nstan&e"tate6E set=ontentiew3%.la'out.main6E

"eek7ar s! , 3"eek7ar6 findiew7'4d3%.id.s!4d6E s!.setHn"eek7ar=hangeBistener3this6E

tv , 3*extiew6 findiew7'4d3%.id.tv4d6E "tring val , this.get"tring3%.string.init_tv_value6E tv.set*ext3val6E I

AHverride pu!li& void on(rogress=hanged3"eek7ar seek7arL int progressL !oolean fromCser6

F tv.set*ext3"tring.valueHf3progress66E I

AHverride

pu!li& void on"tart*ra&king*ou&h3"eek7ar seek7ar6F // not implemented

I

AHverride pu!li& void on"top*ra&king*ou&h3"eek7ar seek7ar6

F // not implemented

II

The current value from the *eek/ar is set to the Text!iew widget.

pu!li& &lass Main)&tivit' extends )&tivit' implementsHn"eek7ar=hangeBistener

The 2ainActivity class implements the )n*eek/ar'hangeListener. 8e neet to define three

abstract methods. The on+rogress'hanged34, the on*tartTrackingTouch34 and the

on*topTrackingTouch34 method. The last two methods are not implemented. They are related

to touch gestures. 8e provide only empty methods.

"eek7ar s! , 3"eek7ar6 findiew7'4d3%.id.s!4d6Es!.setHn"eek7ar=hangeBistener3this6E

8e get the reference to the *eek/ar widget and set a listener for it.

tv , 3*extiew6 findiew7'4d3%.id.tv4d6E"tring val , this.get"tring3%.string.init_tv_value6Etv.set*ext3val6E

8e get the reference to the Text!iew widget. 8e retrieve the init>tv>value from the string

resources and set it to the Text!iew.

AHverridepu!li& void on(rogress=hanged3"eek7ar seek7arL int progressL

!oolean fromCser6F

D7



tv.set*ext3"tring.valueHf3progress66EI

8hen we move the thumb of the *eek/ar, the on(rogress=hanged36 method is called. The

progress parameter is the current value of the *eek/ar. The default range is %..7%%. 8e set

the current value of the *eek/ar to the Text!iew widget.

?igure@ *eek/ar widget

In this chapter of the Android development tutorial, we have written about the *eek/arwidget.

Progress&ar widget

In this chapter of the Android development tutorial we will present the +rogress/ar widget. A

7rogress6ar is a widget that shows visually a progress of some task. The widget comes in

two basic modes. There is a circular bar and a hori"ontal bar.

8e will have two examples to demonstrate both of them.

&rogressBar I

8e have a hori"ontal +rogress/ar widget and a Text!iew widget, that shows the percentage

of the task completed. The manifest file is left untouched.


androidla'out_height,@fill_parent@ <>(rogress7ar

androidid,@AJid/p!4d@ androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@ st'le,@?androidattr/progress7ar"t'le+orizontal@ androidla'out_margin,@1dp@ /<>*extiew androidid,@AJid/tv4d@ androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@

androidla'out_margin,@1dp@ /<>/BinearBa'out<

D$





runHnCi*hread3new %unna!le36 Fpu!li& void run36 F

tv.set*ext3@:inished@6E I I6E

I +andler hnd , new +andler36

FAHverride

pu!li& void handleMessage3Message msg6F

prgJJE p!.set(rogress3prg6E

"tring per& , "tring.valueHf3prg6.to"tring36E tv.set*ext3per&J@Q &ompleted@6E I

IE IEI

8e create a thread to control the progress of a +rogress/ar.

new *hread3m'*hread6.start36E

A new thread is started. In Android, lengthy tasks should by performed inside a thread to

prevent the application from appearing unresponsive. A thread ends by returning from its

main34 method, or by an exception.

AHverridepu!li& void run36F while 3prg > 16 F tr' F hnd.sendMessage3hnd.o!tainMessage366E *hread.sleep316E I &at&h34nterruptedDx&eption e6

FBog.e3@D%%H%@L @*hread was 4nterrupted@6E

I I


tv.set*ext3@:inished@6E I I6EI

The code in a thread is placed in the run36 method. 8e will simulate a lengthy task by

calling the *hread.sleep36 method. This forces us to handle the 0nterrupted8xception.

Android application runs in a single-thread model. All components of the main activity are

DD



created in the main thread. These components cannot be manipulated in other threads. To

work around this, we use either the 9andler obect or call the runHnCi*hread36 method.


tv.set*ext3@:inished@6E II6E

)nly the original thread that created a view hierarchy can touch its views. ere we are

modifying the Text!iew widget. Therefore we have put the code into the runHnCi*hread36

method, which runs the code in the main, <I thread, where the widget was created.

+andler hnd , new +andler36F

AHverride pu!li& void handleMessage3Message msg6

F prgJJE p!.set(rogress3prg6E

"tring per& , "tring.valueHf3prg6.to"tring36E tv.set*ext3per&J@Q &ompleted@6E IIE

Another way to touch widgets from another thread is to use the 9andler obect. It is used to

enueue an action to be performed on a different thread than its own. 8e update the progress

bar and set a percentage of the task completed to the text view.

?igure@ +rogress/ar widget

&rogressBar II

In the second example, we show the usage of the +rogress/ar in a circular mode. The

manifest file does not need to be modified.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@

<>(rogress7arandroidid,@AJid/p!4d@

DG



androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@ /<>*extiew androidid,@AJid/tv4d@ androidla'out_width,@fill_parent@

androidla'out_height,@wrap_&ontent@ androidtext,@Astring/msg@ /<>/BinearBa'out<

In the main.xml file we have a +rogress/ar and a Text!iew. The +rogress/ar has the default

style, which is the circular style. This is the same as if we have used the stle+,:

android#attr/progress6ar5tle, attribute.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es<

>string name,@app_name@<=ir(rog7ar>/string< >string name,@msg@<(lease wait...>/string<>/resour&es<

8e have two string resources in the strings.xml file.

2ainActivity.avapa&kage &om.zet&ode.prog!arE

import android.app.)&tivit'Eimport android.os.7undleEimport android.os.+andlerE

import android.os.MessageEimport android.widget.(rogress7arEimport android.widget.*extiewEimport android.view.iewEimport android.util.BogE

pu!li& &lass Main)&tivit' extends )&tivit'F (rogress7ar p!E *extiew tvE int prg , E

AHverride


p! , 3(rogress7ar6 findiew7'4d3%.id.p!4d6E tv , 3*extiew6 findiew7'4d3%.id.tv4d6E

new *hread3m'*hread6.start36E I

private %unna!le m'*hread , new %unna!le36 F

AHverride pu!li& void run36F

DH



while 3prg > 16 F tr' F hnd.sendMessage3hnd.o!tainMessage366E *hread.sleep316E

I &at&h34nterruptedDx&eption e6F

Bog.e3@D%%H%@L @*hread was 4nterrupted@6E I I


tv.set*ext3@:inished@6E p!.setisi!ilit'3iew.KH0D6E

I I6E

I +andler hnd , new +andler36

FAHverride

pu!li& void handleMessage3Message msg6F

prgJJE p!.set(rogress3prg6E I IE IEI

The code is similar to the first example with a few modifications.


tv.set*ext3@:inished@6E p!.setisi!ilit'3iew.KH0D6E

II6E

After the task was completed, we hide the +rogress/ar using the setisi!ilit'36 method.

The circle itself is an endless animation, so after the task was finished, we need to hide the

widget.

?igure@ 'ircular +rogress/ar widget

In this chapter of the Android development tutorial, we have mentioned +rogress/ar widget.

DB



Listiew widget

In this chapter of the Android development tutorial, we will explore the List!iew widget.

A &ist(iew is a widget that shows items in a verticall scrolling list. An Adapter obect is usedto fill the List!iew with data.

!istView widget I

In the example, we show a List!iew widget with the names of the planets of our solar

system. 8e use an ArrayAdapter to fill the List!iew with data.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@

androidorientation,@verti&al@androidla'out_width,@fill_parent@androidla'out_height,@fill_parent@<

>Bistiewandroidid,@AJid/lv4d@

androidla'out_width,@fill_parent@androidla'out_height,@fill_parent@ /<

>/BinearBa'out<

In the main.xml file we define one List!iew widget.

row.xml>?xml version,@1.@ en&oding,@utf-8@?<>*extiew xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ androidpadding,@1dp@ androidtext"ize,@2sp@<>/*extiew<

In the row.xml file we define, how a list row will look like. 8e will have one Text!iew in

each row of a List!iew. The sp is a unit used for setting the font si"e.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<Bistiew>/string< >string-arra' name,@planets@< >item<Mer&ur'>/item< >item<enus>/item< >item<Darth>/item< >item<Mars>/item< >item<Rupiter>/item< >item<"aturn>/item< >item<Cranus>/item<

>item<0eptune>/item< >item<(luto>/item< >/string-arra'<

DK



>/resour&es<

The names of the planets are specified in the strings.xml file within a string array attribute.

2ainActivity.ava

pa&kage &om.zet&ode.listviewE

import android.app.)&tivit'Eimport android.os.7undleEimport android.widget.)rra')dapterEimport android.widget.BistiewE

pu!li& &lass Main)&tivit' extends )&tivit'F private Bistiew lvE

private )rra')dapter>"tring< laE

AHverride


setupC436E I

pu!li& void setupC436 F

lv , 3Bistiew6 findiew7'4d3%.id.lv4d6E"tringST planets , get%esour&es36.get"tring)rra'3%.arra'.planets6Elv.set)dapter3new )rra')dapter>"tring<3thisL %.la'out.rowL

planets66E II

This is the 2ainActivity.ava source file.

lv , 3Bistiew6 findiew7'4d3%.id.lv4d6E

8e get the reference to the List!iew widget.

"tringST planets , get%esour&es36.get"tring)rra'3%.arra'.planets6E

This code line retrieves the names of the planets from the resource file.

lv.set)dapter3new )rra')dapter>"tring<3thisL %.la'out.rowL planets66E

An ArrayAdapter is created and set to the List!iew.

D



?igure@ List!iew widget

!istView widget II

A &istActivit is a special activity that holds a List!iew obect. List!iew is a common widget

and it typically takes the whole screen. Therefore a special activity was created. In the

example, the manifest file is not modified. 8e will also not need the main.xml layout file.

row.xml>?xml version,@1.@ en&oding,@utf-8@?<>*extiew xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidla'out_width,@fill_parent@

androidla'out_height,@fill_parent@ androidpadding,@1dp@ androidtext"ize,@2sp@<>/*extiew<

In the row.xml file we define one Text!iew in each row of a List!iew.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<Bistiew2>/string<>/resour&es<


2ainActivity.avapa&kage &om.zet&ode.listview2E

import android.app.Bist)&tivit'Eimport android.os.7undleEimport android.view.iewEimport android.widget.)rra')dapterEimport android.widget.)dapteriewEimport android.widget.)dapteriew.Hn4tem=li&kBistenerE

import android.widget.)dapteriew.Hn4tem"ele&tedBistenerEimport android.widget.BistiewEimport android.widget.*extiewE

G%



pu!li& &lass Main)&tivit' extends Bist)&tivit'implements Hn4tem=li&kBistenerL Hn4tem"ele&tedBistener

FAHverride

pu!li& void on=reate37undle saved4nstan&e"tate6

F super.on=reate3saved4nstan&e"tate6E setupC436E I


)rra')dapter>"tring< la , new )rra')dapter>"tring<3thisL%.la'out.row6E

la.add3@Mer&ur'@6E la.add3@enus@6E la.add3@Darth@6E la.add3@Mars@6E

la.add3@Rupiter@6E la.add3@"aturn@6E la.add3@Cranus@6E la.add3@0eptune@6E la.add3@(luto@6E

setBist)dapter3la6E

Bistiew lv , getBistiew36E lv.setHn4tem=li&kBistener3this6E lv.setHn4tem"ele&tedBistener3this6E I

pu!li& void on4tem=li&k3)dapteriew>?< parentL iew viewL int positionL long id6F

"tring planet , 33*extiew6 view6.get*ext36.to"tring36E set*itle3planet6E I

pu!li& void on4tem"ele&ted3)dapteriew>?< parentL iew viewL int positionL long id6

F"tring planet , 33*extiew6 view6.get*ext36.to"tring36E

set*itle3planet6E I

pu!li& void on0othing"ele&ted3)dapteriew>?< parent6F

// not implemented II

8e programatically create the items of the List!iew. 8e react to click and select events of

the List!iew. The planet that we select or click on will be shown in the titlebar.

pu!li& &lass Main)&tivit' extends Bist)&tivit'implements Hn4tem=li&kBistenerL Hn4tem"ele&tedBistener

G7



The 2ainActivity extends the Bist)&tivit' and implements two listeners. /y

implementing these two listeners, we must implement three abstract methods that are

associated with these listeners.

AHverride

pu!li& void on=reate37undle saved4nstan&e"tate6F super.on=reate3saved4nstan&e"tate6E setupC436EI

In the on'reate34 method we do not call the set'ontent!iew34 method. The List!iew widget

of the ListActivity will take up the whole screen.

)rra')dapter>"tring< la , new )rra')dapter>"tring<3thisL %.la'out.row6Ela.add3@Mer&ur'@6Ela.add3@[email protected]@Darth@6E...

8e create an instance of the )rra')dapter. 8e add names of the planets to the adapter.

setBist)dapter3la6E

*ets the adapter for the associated List!iew obect.

Bistiew lv , getBistiew36Elv.setHn4tem=li&kBistener3this6Elv.setHn4tem"ele&tedBistener3this6E

?rom the ListActivity we get the List!iew widget. The two listeners are set for the List!iew

widget.

pu!li& void on4tem=li&k3)dapteriew>?< parentL iew viewL int positionL long id6F

"tring planet , 33*extiew6 view6.get*ext36.to"tring36E set*itle3planet6EI

Implementing the Hn4tem=li&kBistener, we have to define the on4tem=li&k36 method.

8e get the planet name from the *extiew of the clicked row and set it to the titlebar.

pu!li& void on4tem"ele&ted3)dapteriew>?< parentL iew viewL int positionL long id6F

"tring planet , 33*extiew6 view6.get*ext36.to"tring36E set*itle3planet6EI

pu!li& void on0othing"ele&ted3)dapteriew>?< parent6F

// not implementedI

G$



After implementing the Hn4tem"ele&tedBistener we have to define two abstract methods.

The first method sets the currently selected planet to the titlebar. The second method is not

implemented.

?igure@ *elected row of a List!iew widget

In this chapter of the Android development tutorial, we have mentioned the List!iew widget.

Pickers

In this chapter of the Android development tutorial we will talk about android +ickers.+ickers are widgets that enable us to select a single value from a set of values.

There are number, date or time pickers.

'um#er&icker

1umber7ic"er is a widget that allows us to select a number from a predefined range of

values. The manifest file is not modified in this example.

main.xml>?xml version,@1.@ en&oding,@utf-8@?<>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ <

>0um!er(i&ker androidid,@AJid/np4d@ androidla'out_margin*op,@dp@ androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@ /<

>*extiew

androidid,@AJid/tv4d@ androidla'out_width,@wrap_&ontent@

G&



androidla'out_height,@wrap_&ontent@ androidla'out_margin*op,@dp@

androidla'out_marginBeft,@dp@ androidtext,@@ androidtext"ize,@sp@ /<

>/BinearBa'out<

In the layout file we have a 5umber+icker widget and a Text!iew widget. The Text!iew

widget will display the selected value of the 5umber+icker.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<0um!er(i&ker>/string<>/resour&es<

The strings resource file.

2ainActivity.avapa&kage &om.zet&ode.numpi&kE

import android.app.)&tivit'Eimport android.os.7undleEimport android.widget.0um!er(i&kerEimport android.widget.*extiewEimport android.widget.0um!er(i&ker.Hnalue=hangeBistenerE


private *extiew tvE


setupC436E I

pu!li& void setupC436 F tv , 3*extiew6 findiew7'4d3%.id.tv4d6E

0um!er(i&ker np , 30um!er(i&ker6 findiew7'4d3%.id.np4d6E

np.setHnalue=hangedBistener3new Hnalue=hangeBistener36 F pu!li& void onalue=hange30um!er(i&ker pi&kerL int oldalL

int newal6 F tv.set*ext3"tring.valueHf3newal66E

II6E

np.setMaxalue316E np.setMinalue36E I

GD



I

'licking on the plus and minus signs of the 5umber+icker we select a new value. The

currently selected value is displayed in the Text!iew widget.

0um!er(i&ker np , 30um!er(i&ker6 findiew7'4d3%.id.np4d6E

A reference to the 0um!er(i&ker widget is retrieved from the main.xml file.

np.setHnalue=hangedBistener3new Hnalue=hangeBistener36F pu!li& void onalue=hange30um!er(i&ker pi&kerL int oldalL

int newal6 F tv.set*ext3"tring.valueHf3newal66E

II6E

A Hnalue=hangeBistener is added to the 5umber+icker widget. It will call the

onalue=hange36 method when the value of the 5umber+icker is changed. Inside this

method, we set the currently selected value to the Text!iew widget.

np.setMaxalue316Enp.setMinalue36E

8e set the maximum and minimum value for the 5umber+icker.

?igure@ 5umber+icker widget

Time&icker

A *ime7ic"er is a widget for selecting the time of day. It has two modes, $D hour or A20+2

mode. *election of the hour and minute digit can be conrolled by vertical spinners. A

;ate7ic"er is a widget for selecting a date. It is very similar to the Time+icker.

The manifest file is not modified.

GG




<

>*ime(i&ker androidid,@AJid/tp4d@ androidla'out_margin*op,@dp@ androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@ /<

>*extiew androidid,@AJid/tv4d@ androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@ androidla'out_margin*op,@dp@

androidla'out_marginBeft,@dp@

androidtext"ize,@sp@ /<

>/BinearBa'out<

In the main.xml file we have a Time+icker and Text!iew widgets. The selected time is

displayed in the Text!iew.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<*ime(i&ker>/string<>/resour&es<


2ainActivity.avapa&kage &om.zet&ode.timepi&kerE

import android.app.)&tivit'Eimport android.os.7undleEimport android.widget.*ime(i&kerEimport android.widget.*extiewEimport android.widget.*ime(i&ker.Hn*ime=hangedBistenerE

pu!li& &lass Main)&tivit' extends )&tivit'F private *extiew tvE


setupC436E I

pu!li& void setupC436 F tv , 3*extiew6 findiew7'4d3%.id.tv4d6E

GH



*ime(i&ker tp , 3*ime(i&ker6 findiew7'4d3%.id.tp4d6E displa'=urrent*ime3tp6E

tp.setHn*ime=hangedBistener3new Hn*ime=hangedBistener36 F

pu!li& void on*ime=hanged3*ime(i&ker viewL int hourHf#a'Lint minute6 F "tring7uilder tm , new "tring7uilder36E tm.append3hourHf#a'6E tm.append3@ h @6E

tm.append3minute6E tm.append3@ m@6E tv.set*ext3tm6E

II6E

I

pu!li& void displa'=urrent*ime3*ime(i&ker tp6 F int h , tp.get=urrent+our36E int m , tp.get=urrentMinute36E

"tring7uilder tm , new "tring7uilder36E tm.append3h6E tm.append3@ h @6E

tm.append3m6E tm.append3@ m@6E tv.set*ext3tm6E

II

The Time+icker listens to the Hn*ime=hangedBistener . 8hen the time is changed, the new

time value is set to the Text!iew inside the on*ime=hanged36 method.

tp.setHn*ime=hangedBistener3new Hn*ime=hangedBistener36F pu!li& void on*ime=hanged3*ime(i&ker viewL int hourHf#a'L

int minute6 F "tring7uilder tm , new "tring7uilder36E tm.append3hourHf#a'6E tm.append3@ h @6E

tm.append3minute6E tm.append3@ m@6E tv.set*ext3tm6E

II6E

Inside an anonymous Hn*ime=hangedBistener class we implement the on*ime=hanged36

method. 8ith the *tring/uilder we build the string to be displayed and set it to the Text!iew

widget.

pu!li& void displa'=urrent*ime3*ime(i&ker tp6F int h , tp.get=urrent+our36E int m , tp.get=urrentMinute36E

GB



"tring7uilder tm , new "tring7uilder36E tm.append3h6E tm.append3@ h @6E

tm.append3m6E tm.append3@ m@6E tv.set*ext3tm6E

I

8hen the activity is first shown, we display the current time.

?igure@ Time+icker widget

In this chapter of the Android development tutorial, we have written about +ickers.

(enus

In this chapter of the Android development tutorial we will work with menus. 2enus group

available commands of an application. In traditional desktop applications menus are part of a

menubar which is located mostly in the top area of the application. 'ontext or popup menus

are special cases of menus.

There are three kinds of menus in Android. )ptions menu, context menu and popup menu.

The options menu is the primary collection of menu items for an activity. In the options

menu we should have commands that have global impact on the applications. ?or example a

*ettings menu. It is displayed either at the top or at the bottom of the activity. The context

menu shows menu items in a specific context. ?or example for List!iew items. It is shown

when the user performs a long-click on an element. A popup menu displays a list of items in

a vertical list thatFs anchored to the view that invoked the menu. It appears below the anchor

view if there is room, or above the view otherwise. It should relate to regions of content in the

activity.

2enus can be created manually by coding or they can be defined in an E2L file. If we

define our menus in an E2L file we use the Menu0nflater obect to create menus from theE2L file.

GK



(ptions menu

)ur options menu will have two menu items. 8hen we select a menu item a Toast window is

shown with the name of the selected menu item. The options menu is displayed after we click

on the menu button.

The manifest file is not modified in this example.

?igure@ 2enu button

main.xml>?xml version,@1.@ en&oding,@utf-8@?<

>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ < >*extiew

androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@ androidtext,@Astring/message@ /< >/BinearBa'out<

In the main.xml layout file, we have one Text!iew widget. It will display a welcomemessage.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<HptionsMenu>/string< >string name,@message@<#emonstrating Hptions Menu>/string< >string name,@om1@<"ettings>/string< >string name,@om2@<*ools>/string<>/resour&es<

This is strings.xml file.

options>menu.xml>?xml version,@1.@ en&oding,@utf-8@?<>menu xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@< >item androidid,@AJid/settings@ androidtitle,@Astring/om1@ /< >item androidid,@AJid/tools@ androidtitle,@Astring/om2@ /<>/menu<

This is options_menu.xml file. It defines two menu items. The file is located in the res0menu0

subdirectory.

G





Inside the on=reateHptionsMenu36 method, we build the options menu from the

options>menu.xml file. 8e use the Menu4nflater class to do the ob.

AHverridepu!li& !oolean onHptions4tem"ele&ted3Menu4tem item6F...I

The onHptions4tem"ele&ted36 method handles the click events on the menu items.

&ase %.id.settings *oast.make*ext3Main)&tivit'.thisL @"ettings menu sele&ted.@L

*oast.BD0K*+_"+H%*6.show36E return trueE

In case of the selection of the *ettings menu item we show a Toast window with C*ettings

menu selectedC message.

?igure@ )ptions menu at the bottom of the activity

Context menu

8e have a List!iew with the names of our planets. A long-click on an element will show a

context menu with tree options. elete, <ppercase and Lowercase.



H7



>Bistiewandroidid,@AJid/lv4d@

androidla'out_width,@fill_parent@androidla'out_height,@fill_parent@ /<

>/BinearBa'out<

This is main.xml file. It contais a List!iew widget.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<=ontextMenu>/string< >string-arra' name,@planets@< >item<Mer&ur'>/item< >item<enus>/item< >item<Darth>/item<

>item<Mars>/item< >item<Rupiter>/item< >item<"aturn>/item< >item<Cranus>/item< >item<0eptune>/item< >item<(luto>/item< >/string-arra'<>/resour&es<


row.xml>?xml version,@1.@ en&oding,@utf-8@?<>*extiew xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ androidpadding,@1dp@ androidtext"ize,@2sp@<>/*extiew<

This is the row.xml resource file. 9ach row of a List!iew consists of a single Text!iew.

2ainActivity.avapa&kage &om.zet&ode.&onmenuE

import android.app.)&tivit'Eimport android.os.7undleEimport android.widget.)rra')dapterEimport android.widget.BistiewEimport android.view.iewEimport android.view.MenuEimport android.view.Menu4nflaterEimport android.view.Menu4temEimport android.view.=ontextMenuEimport android.view.=ontextMenu.=ontextMenu4nfoEimport android.widget.)dapteriew.)dapter=ontextMenu4nfoE

import ava.util.)rra'sE

import ava.util.)rra'BistE

H$



pu!li& &lass Main)&tivit' extends )&tivit'F private Bistiew lvE

private )rra')dapter>"tring< laE


setupC436E I


lv , 3Bistiew6 findiew7'4d3%.id.lv4d6E"tringST planets , get%esour&es36.get"tring)rra'3%.arra'.planets6E

)rra'Bist>"tring< lst , new )rra'Bist>"tring<36E lst.add)ll3)rra's.asBist3planets66E

la , new )rra')dapter>"tring<3thisL %.la'out.rowL lst6E lv.set)dapter3la6E register:or=ontextMenu3lv6E I

AHverride pu!li& void on=reate=ontextMenu3=ontextMenu menuL iew vL

=ontextMenu4nfo menu4nfo6F

super.on=reate=ontextMenu3menuL vL menu4nfo6E

Menu4nflater inflater , getMenu4nflater36E inflater.inflate3%.menu.&ontext_menuL menu6E I

AHverride pu!li& !oolean on=ontext4tem"ele&ted3Menu4tem item6

F )dapter=ontextMenu4nfo info , 3)dapter=ontextMenu4nfo6item.getMenu4nfo36E

int pos , info.positionE "tring i , la.get4tem3pos6E

swit&h 3item.get4tem4d366F

&ase %.id.del4d la.remove3i6E return trueE

&ase %.id.up4d"tring upln , i.toCpper=ase36E

la.remove3i6E la.insert3uplnL pos6E

return trueE

&ase %.id.lo4d "tring lpln , i.toBower=ase36E la.remove3i6E la.insert3lplnL pos6E

H&



return trueE

default return super.on=ontext4tem"ele&ted3item6E I I

I

In order to implement the context menu, we have to override the on=reate=ontextMenu36

and the on=ontext4tem"ele&ted36 methods. 8e also need to call the

register:or=ontextMenu36 method for a specific view.

"tringST planets , get%esour&es36.get"tring)rra'3%.arra'.planets6E)rra'Bist>"tring< lst , new )rra'Bist>"tring<36Elst.add)ll3)rra's.asBist3planets66E

8e will be deleting items of the List!iew. Therefore, we need to use an ArrayList. )therwise

the list would be read-only.

register:or=ontextMenu3lv6E

The context menu is registered for the List!iew widget.

AHverridepu!li& void on=reate=ontextMenu3=ontextMenu menuL iew vL

=ontextMenu4nfo menu4nfo6F super.on=reate=ontextMenu3menuL vL menu4nfo6E Menu4nflater inflater , getMenu4nflater36E inflater.inflate3%.menu.&ontext_menuL menu6EI

In the on=reate=ontextMenu36 method we build the context menu from the

context>menu.xml file.

AHverridepu!li& !oolean on=ontext4tem"ele&ted3Menu4tem item6F...I

The on=ontext4tem"ele&ted36 reacts to list item selection events.

)dapter=ontextMenu4nfo info , 3)dapter=ontextMenu4nfo6 item.getMenu4nfo36E

int pos , info.positionE"tring i , la.get4tem3pos6E

To find out more about the selected item, we use the )dapter=ontextMenu4nfo class. 8e

get the position and the text of the selected item.

&ase %.id.del4d la.remove3i6E

return trueE

HD



If we select the elete context menu option, we remove the item from the ArrayAdapter.

&ase %.id.up4d"tring upln , i.toCpper=ase36E

la.remove3i6E la.insert3uplnL pos6E

return trueE

?or the <ppercase option, we modify the string, remove the original one and insert a new

one.

?igure@ 'ontext menu with three options

&opup menu

The example shows a +opup2enu after clicking on a button.


main.xml>?xml version,@1.@ en&oding,@utf-8@?<

>BinearBa'out xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidorientation,@verti&al@ androidla'out_width,@fill_parent@ androidla'out_height,@fill_parent@ < >7utton

androidid,@AJid/!tn4d@ androidla'out_height,@wrap_&ontent@ androidla'out_width,@wrap_&ontent@ androidla'out_margin*op,@1dip@ androidtext,@Astring/!tn_la!el@ androidon=li&k,@on=li&k@ /<

>*extiew

HG



androidid,@AJid/tv4d@ androidla'out_width,@fill_parent@ androidla'out_height,@wrap_&ontent@

androidla'out_margin*op,@1dip@ /< >/BinearBa'out<

This is main.xml file. 8e have a /utton widget and a Text!iew widget. The button will show

a +opup2enu.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<(opupMenu>/string< >string name,@!tn_la!el@<"how menu>/string< >string name,@pm1@<4tem 1>/string< >string name,@pm2@<4tem 2>/string<>/resour&es<


popup>menu.xml>?xml version,@1.@ en&oding,@utf-8@?<>menu xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@< >item androidid,@AJid/settings@ androidtitle,@Astring/pm1@ /< >item androidid,@AJid/tools@ androidtitle,@Astring/pm2@ /<>/menu<

This is popup_menu.xml file. It defines two menu items. The file is located in the res0menu0subdirectory.

2ainActivity.avapa&kage &om.zet&ode.popmenuE

import android.app.)&tivit'Eimport android.os.7undleEimport android.view.iewEimport android.view.Menu4temEimport android.widget.*extiewEimport android.widget.(opupMenuE

import android.widget.(opupMenu.HnMenu4tem=li&kBistenerE

pu!li& &lass Main)&tivit' extends )&tivit' implements HnMenu4tem=li&kBistenerF

private *extiew tvE


tv , 3*extiew6 findiew7'4d3%.id.tv4d6EI

HH



pu!li& void on=li&k3iew v6F

show(opupMenu3v6E I

pu!li& void show(opupMenu3iew v6

F (opupMenu pm , new (opupMenu3Main)&tivit'.thisL v6E pm.getMenu4nflater36.inflate3%.menu.popup_menuL pm.getMenu366E

pm.setHnMenu4tem=li&kBistener3this6Epm.show36E

I

AHverride pu!li& !oolean onMenu4tem=li&k3Menu4tem item6

Ftv.set*ext3item.to"tring36 J @ sele&ted@6E

return trueEI

I

A +opup2enu is displayed after clicking on the button widget.

pu!li& void on=li&k3iew v6F

show(opupMenu3v6EI

This method is a callback to the button click. The relation is set in the main.xml file via an

attribute. The method calls the show+opup2enu34 method.

pu!li& void show(opupMenu3iew v6F (opupMenu pm , new (opupMenu3Main)&tivit'.thisL v6E pm.getMenu4nflater36.inflate3%.menu.popup_menuL pm.getMenu366E

pm.setHnMenu4tem=li&kBistener3this6Epm.show36E

I

8e create an instance of the (opupMenu class. It builds the menu, sets the

HnMenu4tem=li&kBistener and shows the (opupMenu.

AHverride

pu!li& !oolean onMenu4tem=li&k3Menu4tem item6F

tv.set*ext3item.to"tring36 J @ sele&ted@6E return trueEI

After selecting a menu item the onMenu4tem=li&k36 method is called. It sets the itemFs title

to the Text!iew widget.

In this chapter of the Android development tutorial, we have worked with menus.

"ialogs

HB



In this chapter of the Android development tutorial we will talk about dialogs. 8e will

discuss the Android Alertialog.

A dialog is defined as a conversation between two or more persons. In a computer application

a dialog is a window which is used to CtalkC to the application. A dialog is used to input data,

modify data, change the application settings etc.

An Alert;ialog is a dialog used to display information or receive data. It can display one, two

or three buttons. It is created with a /uilder subclass.

Displa"ing a message

8e will use the Alertialog to display a message. In the example, we do not need to modify

the manifest file.


>7utton androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@ androidla'out_margin*op,@1dip@ androidon=li&k,@on=li&ked@ androidtext,@Astring/!tn_la!el@ /< >/BinearBa'out<

In the main.xml layout file, we have a /utton widget. This button will display an Alertialog.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<#ispla'"ize>/string< >string name,@!tn_la!el@<"how>/string<>/resour&es<

This is strings.xml file.

2ainActivity.avapa&kage &om.zet&ode.displa'sizeE

import android.app.)&tivit'Eimport android.os.7undleEimport android.view.iewEimport android.graphi&s.(ointEimport android.app.)lert#ialogEimport android.&ontent.#ialog4nterfa&eEimport android.view.NindowManagerE

import android.view.#ispla'E

HK




AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E

set=ontentiew3%.la'out.main6E I

pu!li& void on=li&ked3iew view6 F (oint p , get#ispla'"ize36E

)lert#ialog ad , new )lert#ialog.7uilder3this6.&reate36E

ad.set*itle3@#ispla' size@6E "tring msg , "tring.format3@NidthQdL +eightQd@L p.xL p.'6E ad.setMessage3msg6E ad.set4&on3android.%.drawa!le.i&_dialog_info6E

ad.set7utton3@H@L new #ialog4nterfa&e.Hn=li&kBistener36 F pu!li& void on=li&k3#ialog4nterfa&e dialogL int whi&h6 F dialog.&an&el36E I I6E

ad.show36EI

pu!li& (oint get#ispla'"ize36 F NindowManager wm , 3NindowManager6

get"'stem"ervi&e3N40#HN_"D%4=D6E #ispla' ds , wm.get#efault#ispla'36E

(oint p , new (oint36E ds.get"ize3p6E

return pE II

8e use the Alertialog to display the si"e of the display.

(oint p , get#ispla'"ize36E

In the custom getisplay*i"e34 method, we determine the si"e of the display.

)lert#ialog ad , new )lert#ialog.7uilder3this6.&reate36E

An instance of the )lert#ialog is created.

ad.set*itle3@#ispla' size@6E"tring msg , "tring.format3@NidthQdL +eightQd@L p.xL p.'6Ead.setMessage3msg6Ead.set4&on3android.%.drawa!le.i&_dialog_info6E

8e set a title, message and an icon for the dialog.

H



ad.set7utton3@H@L new #ialog4nterfa&e.Hn=li&kBistener36 F pu!li& void on=li&k3#ialog4nterfa&e dialogL int whi&h6 F dialog.&an&el36E II6E

8e add a button to the dialog. 8hen we click on the )= button, the dialog is closed.

ad.show36E

The show36 method shows the dialog.

NindowManager wm , 3NindowManager6 get"'stem"ervi&e3N40#HN_"D%4=D6E#ispla' ds , wm.get#efault#ispla'36E

8e get the default display.

(oint p , new (oint36Eds.get"ize3p6E

8e find out the si"e of the display with the get"ize36 method.

?igure@ Alertialog showing the si"e of the display

Recei$ing data

The second example uses the Alertialog to receive data from a user. The dialog will ask a

user for his name. It will then display the input in a Text!iew widget.


B%




<

>7utton androidid,@AJid/!tn4d@ androidla'out_width,@wrap_&ontent@ androidla'out_height,@wrap_&ontent@ androidla'out_margin*op,@1dip@ androidon=li&k,@on=li&ked@ androidtext,@Astring/!tn_la!el@ /<

>*extiew androidid,@AJid/tv4d@ androidla'out_width,@fill_parent@

androidla'out_height,@wrap_&ontent@ /< >/BinearBa'out<

This is main.xml file. 8e have a /utton widget and a Text!iew widget. The button will show

the dialog window. The Text!iew will receive the input text from the dialog.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<4nput#ialog>/string< >string name,@!tn_la!el@<"how dialog>/string<

>/resour&es<


2ainActivity.avapa&kage &om.zet&ode.inputE

import android.app.)&tivit'Eimport android.os.7undleEimport android.app.)lert#ialogEimport android.view.iewEimport android.widget.Ddit*extE

import android.widget.*extiewEimport android.&ontent.#ialog4nterfa&eE

pu!li& &lass Main)&tivit' extends )&tivit'F private *extiew tvE


tv , 3*extiew6 findiew7'4d3%.id.tv4d6E I

B7



pu!li& void on=li&ked3iew view6 F )lert#ialog.7uilder ad , new )lert#ialog.7uilder3this6E

ad.set*itle3@4nput@6E ad.setMessage3@Dnter 'our name@6E

final Ddit*ext input , new Ddit*ext3this6E ad.setiew3input6E

ad.set(ositive7utton3@Hk@L new #ialog4nterfa&e.Hn=li&kBistener36 F pu!li& void on=li&k3#ialog4nterfa&e dlgL int whi&h6 F "tring val , input.get*ext36.to"tring36E "tring msg , "tring.format3@+ello QsU@L val6E tv.set*ext3msg6E I I6E

ad.set0egative7utton3@=an&el@L new

#ialog4nterfa&e.Hn=li&kBistener36 F pu!li& void on=li&k3#ialog4nterfa&e dlgL int whi&h6 F dlg.&an&el36E I I6E

ad.show36E II

'licking on the button widget will display the Alertialog. It has an 9ditText to receive the

input from a user.

)lert#ialog.7uilder ad , new )lert#ialog.7uilder3this6E

ad.set*itle3@[email protected]@Dnter 'our name@6E

8e set a title and a message for the dialog.

final Ddit*ext input , new Ddit*ext3this6Ead.setiew3input6E

8e add the Ddit*ext widget to the dialog.

ad.set(ositive7utton3@Hk@L new #ialog4nterfa&e.Hn=li&kBistener36 Fpu!li& void on=li&k3#ialog4nterfa&e dlgL int whi&h6 F "tring val , input.get*ext36.to"tring36E "tring msg , "tring.format3@+ello QsU@L val6E tv.set*ext3msg6E II6E

'licking on the )= button of the dialog, we get the text from the 9ditText widget. The text

used to format a greeting which is set to the Text!iew.

ad.set0egative7utton3@=an&el@L new #ialog4nterfa&e.Hn=li&kBistener36 F pu!li& void on=li&k3#ialog4nterfa&e dlgL int whi&h6 F dlg.&an&el36E

B$





bitmaps. A ;rawable is an obect that can be drawn. <nlike a !iew, a rawable does not

have any facility to receive events or otherwise interact with the user.

($al shape

8e are going to draw a circle on a !iew. The circle is defined in an E2L file. The manifestfile does not need to be modified.

oval.xml>?xml version,@1.@ en&oding,@utf-8@?<>shape xmlnsandroid,@http//s&hemas.android.&om/apk/res/android@ androidshape,@oval@<

>solidandroid&olor,@VWWWWWW@/<

>sizeandroidwidth,@5dp@

androidheight,@5dp@/<>/shape<

In the oval.xml file we create a circle shape. 8e define its colour and si"e. The oval.xml file

is located in the res0drawable directory. The directory had to be created.


<

>iew androidla'out_width,@1dp@ androidla'out_height,@1dp@ androidla'out_margin*op,@dp@ android!a&kground,@Adrawa!le/oval@ /<

>/BinearBa'out<

In the main.xml file, we define a simple !iew. The background of this view is filled with our

drawable obect.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<Hval"hape>/string<>/resour&es<

6esources file.

2ainActivity.avapa&kage &om.zet&ode.ovalshapeE

import android.app.)&tivit'Eimport android.os.7undleE

BD



pu!li& &lass Main)&tivit' extends )&tivit'F AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F

super.on=reate3saved4nstan&e"tate6E set=ontentiew3%.la'out.main6E II

The file ust loads the defined layout.

?igure@ )val *hape

Drawing a rectangle

In the second example, we will draw a rectangle on a !iew. It will be drawn in the on#raw36

method of the !iew. *ince we will be drawing on an existing !iew, we will have a

predefined 'anvas with its /itmap. 8e do not need to worry about them. The manifest file isnot modified. In this example the main.xml file will not be needed.

strings.xml>?xml version,@1.@ en&oding,@utf-8@?<>resour&es< >string name,@app_name@<#raw%e&t>/string<>/resour&es<

6esources.

raw!iew.avapa&kage &om.zet&ode.drawre&tE

import android.&ontent.=ontextEimport android.graphi&s.=anvasEimport android.graphi&s.=olorEimport android.graphi&s.(aintEimport android.view.iewE

pu!li& &lass #rawiew extends iewF (aint paint , new (aint36E

pu!li& #rawiew3=ontext &ontext6

F super3&ontext6E

BG



paint.set=olor3=olor.K%DD06E I

AHverride pu!li& void on#raw3=anvas &anvas6

F

&anvas.draw%e&t3L L 1L 1L paint6E II

8e have a custom raw!iew class. The file is located in the src0com0"etcode0drawrect0

directory.

pu!li& &lass #rawiew extends iew

The custom raw!iew class inherits from the base !iew class.

(aint paint , new (aint36E

An instance of the +aint class is created. It will define a colour for drawing.

paint.set=olor3=olor.K%DD06E

8e will paint in green colour.

AHverridepu!li& void on#raw3=anvas &anvas6F &anvas.draw%e&t3L L 1L 1L paint6E

I

The drawing is performed in the on#raw36 method. The method provides the =anvas obect

for us. 8e call the draw%e&t36 to draw the rectangle on the !iew.

2ainActivity.avapa&kage &om.zet&ode.drawre&tE

import android.app.)&tivit'Eimport android.graphi&s.=olorEimport android.os.7undleE

pu!li& &lass Main)&tivit' extends )&tivit'F AHverride pu!li& void on=reate37undle saved4nstan&e"tate6 F super.on=reate3saved4nstan&e"tate6E

#rawiew drawiew , new #rawiew3this6E drawiew.set7a&kground=olor3=olor.N+4*D6E set=ontentiew3drawiew6E II

In the 2ainActivity.ava source file we set the custom raw!iew to be the content !iew ofthe Activity.

BH



#rawiew drawiew , new #rawiew3this6E

8e create an instance of the #rawiew class.

drawiew.set7a&kground=olor3=olor.N+4*D6E

8e specify the background colour for the !iew.

set=ontentiew3drawiew6E

The raw!iew becomes the content !iew of the Activity.

?igure@ 6ectangle

In this chapter of the Android development tutorial, we did dome basic drawing.

Documents

ZetCode Android Tutorial