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8Chapter ObjectivesChapter Objectives
• Declare and use object variables• Create procedures that use built-in form
methods• Find and manipulate data with recordset
objects• Execute parameter queries in VBA• Communicate with other applications with
Automation objects
8Chapter ObjectivesChapter Objectives
• Find methods through the Object Browser
• Create class modules
• Open multiple form instances with user-defined objects
• Describe the features of a well-designed, object-based application
8 The World According to Methods
The World According to Methods
• Access uses objects and properties because people understand and use them in their daily lives and thus can easily apply the concepts to programming
• Method Procedure or action that belongs to an object
8Overview of Access MethodsOverview of Access Methods
• Access methods perform actions
Figure 8-1 NewDegreeType procedure
8Overview of Access MethodsOverview of Access Methods
Figure 8-1 NewDegreeType procedure (continued)
8Overview of Access MethodsOverview of Access Methods
• Facts about methods: RunCommand method
Similar to RunCommand macro actionDoCmd.RunCommand acCmdUndo erases the
user’s most recent entry from the form
Open methodWhen applied to a recordset object, the recordset
can access data in the table or query that is specified in the Source argument
8Overview of Access MethodsOverview of Access Methods
• Facts about methods (continued): AddNew method
Attached to a recordset objectCauses a recordset to create space for a new record
Update methodCauses the recordset to write the new record to the
database Close method
Removes the reference to the recordset
8Object VariablesObject Variables
• To invoke a method, the associated object must be referenced
• Dot and bang notations Allow the identification of specific forms,
reports, controls, tables, or fields Can be used when invoking a method
8Object VariablesObject Variables
• Dot and bang notation disadvantages: Can be long Not very efficient when used repeatedly
• Object variables Variables used in VBA procedures that contain a
pointer to the item of interest Efficient reference to Access application objects Must be used to reference DAO and ADO objects
8 Declaring and Setting Object Variables
Declaring and Setting Object Variables
• Declaration statements declare variables as String, Long, Integer, and so on
• VBA statements are similar to those found in many other procedural languages
• In VBA, data types used in declaration statements can also include objects
8 Another Technique for Setting Object VariablesAnother Technique for
Setting Object Variables
• Declare a control object variable and then set the object variable to the control that currently has the focus Control is identified by the ActiveControl
property of the Screen object Technique is used when a procedure can work
with whatever control has the focus
8 Built-in Methods Related to Microsoft Access Objects
Built-in Methods Related to Microsoft Access Objects
• Microsoft Access objects, including forms, reports, and applications, support many built-in methods
• Some objects, including forms, reports, and independent class modules, support the creation of custom methods
8DoCmd MethodsDoCmd Methods
• DoCmd objects Never manipulated by its methods, but those
methods frequently manipulate another object
• DoCmd methods Exist for almost every action that can be
selected from a macro’s action column Name matches a macro action Arguments usually correspond to the macro’s
action arguments
8 The RunCommand Method and Its Intrinsic Constants
The RunCommand Method and Its Intrinsic Constants
• Action performed by the RunCommand method depends on the value of its command argument Intrinsic constants is used to specify that value
Exist for almost all of the controls listed in the Access built-in menu bars
8 The RunCommand Method and Its Intrinsic Constants
The RunCommand Method and Its Intrinsic Constants
Figure 8-2 Deleting a record from frmStudentQDrops
8Form and Control MethodsForm and Control Methods
• Data shown on a form might not be current because: The recordset generated for the form may not
reflect recent changes to the databaseRefreshing a recordset refers to the process of
updating the fields of all records currently in the recordset
Requerying a form completely regenerates the recordset
8Form and Control MethodsForm and Control Methods
• Data on a form may not be current because (continued): A calculated control may not recalculate its
expression after the value of a control used in expression changes Calculated control should be recalculated
The form may know the correct values to display, but because Access is executing other procedures, it does not have time to display correct values Form needs repainting
8 Methods that Update Displayed Data
Methods that Update Displayed Data
• Access automatically refreshes, recalculates, and repaints forms at Access-defined intervals Refresh interval
Specified in the database’s Option window
8 Methods that Update Displayed Data
Methods that Update Displayed Data
• Refresh method To refresh the recordset
• Recalc method To cause a recalculation of the form’s calculated
controls
• Repaint method To force the system to repaint the screen
• Requery method To force Access to regenerate a recordset
8 Methods that Update Displayed Data
Methods that Update Displayed Data
Figure 8-4 Refreshing and requerying a form
8 Methods that Update Displayed Data
Methods that Update Displayed Data
Table 8-2 Form and control methods
8 Methods that Update Displayed Data
Methods that Update Displayed Data
Table 8-2 Form and control methods (continued)
8 Report, Module, and Application MethodsReport, Module, and Application Methods
• Application object Frequently used in Access applications
• Methods of the Application object: Echo Method
Used in conjunction with DoCmd’s HourGlass method
Turns screen updating off while several changes occur to the form
8 Report, Module, and Application MethodsReport, Module, and Application Methods
Table 8-3 Commonly used Application object methods
8ADO and DAO MethodsADO and DAO Methods
• Methods related to ActiveX Data Objects (ADO) and Data Access Objects (DAO) perform many operations including: Connecting to the database Executing queries Updating data not currently displayed in form
• ADO is replacing DAO as the standard method for manipulating data in Microsoft products
8 Methods of the Connection Object
Methods of the Connection Object
• Almost all procedures that use ADO objects require a Connection object Identifies and opens the database that contains
the tables and queries that are used within the procedure
Establishes a connection to a database that will be manipulated in VBA code
8 Methods of the Connection Object
Methods of the Connection Object
• Methods of a Connection Object: Close method
Shuts down the pathway to the database
Execute methodCan be used to execute queries
8 Executing Queries in VBA Through the Command Object
Executing Queries in VBA Through the Command Object
• The Execute method associated with the Command object in VBA causes a query to run
Figure 8-6 qryDeleteDeniedProspects
8Query ParametersQuery Parameters
• Frequently, action queries triggered in VBA code use VBA parameters
• Advantage of parameters is that the query will retrieve or update different data depending on the parameters’ values
• To execute a parameter query in VBA, the values of the parameters must be supplied
8Opening RecordsetsOpening Recordsets
• Programmers can use recordsets to locate and update data Must declare and set a recordset object variable Must open a pathway to the table or query that
contains the data through the Open method
• Recordset objects can be created from other recordset objects through the Clone method
8 Finding Records in a Recordset
Finding Records in a Recordset
• Bookmark property of a recordset A string expression that uniquely identifies the current
record
• AbsolutePosition property A long integer that contains the ordinal position of the
current record
• MoveFirst, MoveLast, MovePrevious, and MoveNext methods Used for simple movements to new records
8 Finding Records in a Recordset
Finding Records in a Recordset
• Move method Used in conjunction with a long integer to
move the specified number of records forward
• Seek method Used to search a recordset through the primary
key or indexes
• Filter propertySimilar to a form’s filter property
8 Editing, Deleting, and Updating Data in a Recordset
Editing, Deleting, and Updating Data in a Recordset
• Programmers frequently use recordsets to edit, delete, and update records
• Recordset methods specify how the data are to be updated
• Recordsets must be opened with a LockType that permit updating of the database
8Using DAO RecordsetsUsing DAO Recordsets
• Methods of DAO recordset FindFirst, FindNext, FindPrevious, and
FindLastSimilar to ADO’s Find method
AddNew, Update, and DeleteAlmost identical to their ADO counterparts
EditMust be executed before values in an existing record
are changed
8Using DAO RecordsetsUsing DAO Recordsets
• RecordsetClone property of a form Returns a pointer to the recordset
• NoMatch property Used to indicate whether the previous Find
method failed to find a match
8 ADO and DAO Methods – Some Final Thoughts
ADO and DAO Methods – Some Final Thoughts
• CompactDatabase method Associated with the JetEngine object Makes the database smaller
• Append method Places newly created objects in a collection
• Delete method of a collection object Removes an object from the collection
8The Object BrowserThe Object Browser
• The Object Browser is available in the Visual Basic Editor (VBE)
Figure 8-8 Object Browser for VBA Collection Add method
8 Automation Object Variables and Methods
Automation Object Variables and Methods
• GetObject function Returns a pointer to objects in another Windows
application called the source application
• Automation object variable Any variable that references an object contained in
another application
• CreateObject function Used to create new applications in Access
8 Object-Based Approach to Application Development
Object-Based Approach to Application Development
• The object-based philosophy of Access provides some guidance as to how an application should be organized
• Many objects make up an Access application Most possess the ability to test or manipulate
their own features
8 Object-Based Approach to Application Development
Object-Based Approach to Application Development
• Other objects such as collections and forms possess abilities that perform certain operations on themselves Procedures outside the object need to know
only which methods are available and what the methods do
• A benefit of locating methods with objects that they manipulate is that many objects can use the same method
8 Object-Based Approach to Application Development
Object-Based Approach to Application Development
• “Rules of thumb” for designing Access applications: Organize procedures based on the object being
manipulated Try to build objects that can be reused Build Objects that are not highly coupled with
other objects
8 Opening Multiple Instancesof a Form
Opening Multiple Instancesof a Form
• User-defined object Class object that can be used to create other
objects
• Class object A model of an object
• Instances of the class object Objects that are based on a class
8 Creating and Using Independent Class Modules
Creating and Using Independent Class Modules
• Independent class modules Contain sub procedures and functions Can also contain Let and Get property
procedures Treated as an object
• Class modules can also invoke events• Because a class module is an object,
instances of the object can be created
8Chapter SummaryChapter Summary
• In VBA objects and properties are manipulated and created by methods Access supplies built-in methods You can create your own methods
• Objects can be identified through the dot and bang notations Object variables shortens notation
• Object variables can be declared as any recognized ADO, DAO, or Microsoft Access object type
8Chapter SummaryChapter Summary
• Form objects are associated with several built-in methods Requery tells form to regenerate its recordset Recalc, Refresh, and Repaint ensure that
Access is displaying the correct data on a form
• DoCmd object offers many methods for manipulating data on a form
8Chapter SummaryChapter Summary
• Recordsets can be created with several methods and properties Recordset methods locate or change data in a table
• Filling parameters and executing an action query in VBA code updates data
• Automation object variables allow VBA in Access to use and manipulate objects in other languages such as Word and Excel