DATABASE AUTOMATION USING VBA (ADVANCED MICROSOFT ACCESS, X405.6)

Transcription

1 Technology & Information Management Instructor: Michael Kremer, Ph.D. Database Program: Microsoft Access Series DATABASE AUTOMATION USING VBA (ADVANCED MICROSOFT ACCESS, X405.6) Section 4

2 AGENDA 7. Working with Objects

3 Working with Objects 7.

4 7.1 OVERVIEW OF OBJECTS 96 VBA is a OO programming language. Collection of objects exposed by an application (such as MS Word) is called a library. You can use multiple libraries in Access VBA. Object is a physical thing having properties, methods and events. An object can contain other objects, these objects are organized in the object hierarchy. Properties: Physical attribute having multiple possible values.

5 7.1 OVERVIEW OF OBJECTS 97 Some properties can be set, while others can only be read (inherent properties). Methods: Action that can be performed by or on an object. Events: Something that happens to an object. Events and methods are related in a cause-and-effect way. An event happens when the user does something, the actual doing is the method. The difference between event and method is sometimes not as clear.

6 7.2 OBJECTS IN MS ACCESS 98 Navigation Pane (Main Database Window) lists main objects. Many more objects in MS Access, they are all organized in a hierarchical way. MS Access is comprised of DB, Application layer and VBA, each has its own object hierarchy. Refer to these objects by using a reference variable.

7 7.2 OBJECTS IN MS ACCESS 99

8 7.3 THE COLLECTION OBJECT 100 There are many objects in MS Access. Collection object serves as a container to group objects of similar properties and behaviors. Most common properties of a collection object: Count: Number of objects contained in the collection. Item: Reference to specific object in the collection. Parent: Reference to parent object. Example: Loop through collection of tables

9 7.3 THE COLLECTION OBJECT 101

10 7.3 THE COLLECTION OBJECT Tables collection also includes system tables (prefix Msys). To differentiate between a single object and a collection of objects, use plural s. For example, Forms. Within a form, there is the Controls collection. Forms Collection 102 Customer Form CustomerPets Form Controls Collection Controls Collection CommandButton Label PetName textbox Line

11 7.3 THE COLLECTION OBJECT 103 Once a form is referenced, the controls collection of that form needs to be referenced to reach an individual control. It is important to distinguish between singular and collection objects when building references.

12 7.4 NAVIGATING OBJECT HIERARCHY 104 All objects, whether singular or not, are somehow related to each other. Forms Form Controls Control Which object contains which object is determined by the Object Hierarchy. Similar to relational database. Diagrams are used to show object hierarchies. We are going to look at one small part of the entire object hierarchy, the table object hierarchy. Tables and queries are special, as they actually contain two different objects: Table definition or structure: TableDef object Table data: Recordset object

13 7.4 NAVIGATING OBJECT HIERARCHY 105 TableDefs is a collection of all tables. Within that collection, a TableDef objects Within a TableDef objects, the collection of fields, indexes, and properties.

14 7.4 NAVIGATING OBJECT HIERARCHY 106 Fields Table Properties Indexes Field Properties

15 7.4 NAVIGATING OBJECT HIERARCHY 107 Complete TableDefs collection

16 7.4 NAVIGATING OBJECT HIERARCHY 108 TableDef object model belongs to the database. Input Mask, Format are properties added through the application layer. Application Layer also contains a table collection object, simply to manage tables within the access application. Partial object hierarchy of Application Object application CurrentData Forms CurrentProject AllDatabaseDiagrams(ADP) AllFunctions(ADP) AllQueries AllStoredProcedures(ADP) AllTables AllViews(ADP) Reports Modules Screen AllForms AllMacros AllModules AllReports Properties DoCmd

17 7.4 NAVIGATING OBJECT HIERARCHY 109 Application hierarchy also contains many singular objects, two of them are shown here. DoCmd object allows you to run any menu command programmatically. Screen object refers to the currently active object. DoCmd Application Object Screen Forms Modules Reports Form Module Report Controls Controls Control Module Module Control

18 7.4 NAVIGATING OBJECT HIERARCHY 110 VBA object hierarchy: VBA collection object is different than a collection object. Err object is used for keeping track of errors. Debug object is used for debugging tools. Database Object Hierarchy is probably most complex one. Two main collection objects are Workspace and Errors collection. Main object is DBEngine.

19 7.4 NAVIGATING OBJECT HIERARCHY 111 Workspaces are used to isolate transactions from each other. Users and Groups collections are contained within a workspace. Groups are created to assign multiple permissions to multiple users. Users may belong to multiple groups. Database collection is contained within a workspace.

20 7.5 REFERRING TO OBJECTS 112 In order to manipulate objects using VBA, a specific syntax needs to be followed to refer to that object. Knowing the object hierarchy makes this task easier. To correctly refer to an object, one must travel from the top (application object) to the desired object. Collections play an important role, in that an object within a collection must be identified as a member of that collection. Forms![frm_Employees].Caption Three ways to refer to an object: Index by Name, Index by Variable, Index by Position

21 7.5 REFERRING TO OBJECTS 113

22 7.5 REFERRING TO OBJECTS 114 Start at the top of the hierarchy, this is the application object. The exclamation mark (!) (or bang operator) is used to step from a collection to one of its members. CollectionName! ObjectName dot operator is used to step from an object to one of its collection ObjectName. CollectionName Application.Forms![Employees].Controls![FirstName]

23 7.5 REFERRING TO OBJECTS 115 References can become quite complex, when using Expression Builder references may look different. Take advantage of Default collections: Object having more than one collection has a default collection determined by MS Access. Object having only one collection has a default of that collection. Fully qualified: Application.Forms![Employees].Controls![FirstName] Simplified: Forms![Employees]![FirstName]

24 7.5 REFERRING TO OBJECTS 116 Intelli-Sense for building references. References in main/sub configuration Forms![MainFormName].Controls![SubformControlName] Again we can leave the default collection controls out of the syntax: Forms![MainFormName]![SubformControlName] To refer to the properties of the subform control, use the dot operator: Forms![MainFormName]![SubformControlName].Properties

25 7.5 REFERRING TO OBJECTS 117

26 7.5 REFERRING TO OBJECTS 118 To refer to the subform contained in the subform control: Forms![MainFormName].Controls![SubformControlName].Form.Property

27 7.5 REFERRING TO OBJECTS 119 To refer to a control on a subform, the fully qualified syntax is: Forms![MainFormName].Controls![SubformName].Form.Controls![ControlName]

28 7.5 REFERRING TO OBJECTS 120

29 7.6 OBJECT VARIABLES 121 Object references can become quite lengthy. Use Object variables, data type of Object. Object variable does not hold the object itself, it simply holds the reference to the object in memory.

30 7.6 OBJECT VARIABLES 122 When assigning object variables, you must use the Set keyword. Remember, Let keyword was optional. Once reference is not needed anymore, use Set ctl = Nothing

31 7.6 OBJECT VARIABLES 123

32 7.7 WORKING WITH OBJECTS IN COLLECTIONS 124 Looping through the Controls Collection.

33 7.7 WORKING WITH OBJECTS IN COLLECTIONS 125 Count of controls included all types of control, including labels and command buttons. Controls can be very different, yet they are all contained in one collection. Violates basic principle of a collection. Read-only property at the control object named ControlType enables us to differentiate between different types of controls. Loop through controls:

34 7.7 WORKING WITH OBJECTS IN COLLECTIONS 126

35 7.7 WORKING WITH OBJECTS IN COLLECTIONS 127 Use ControlType property to affect only one type of control: actextbox (109) aclabel (100) accombobox (111) aclistbox (110) accheckbox (106) actabctl (123) acoptionbutton (105) acsubform (112) acimage (103) acline (102) acoptiongroup (107) acrectangle (101)

36 7.7 WORKING WITH OBJECTS IN COLLECTIONS 128

37 7.8 OBJECT PROPERTIES 129 Using VBA, properties can be set at run-time. Same properties as in the property sheet in design view. However, additionally properties are exposed in VBA. Forms![frm_Customer].Controls![CustomerName].Properties.ControlSource

38 7.8 OBJECT PROPERTIES 130 When referencing properties or methods, must use dot operator: Forms![frm_Customer]![CustomerName].ControlSource Two actions can be taken when working with properties : Change the value of a property, that is set the property Read the value of a property, that is get the property

39 7.9 OBJECT METHODS 131 A method is a programmed behavior that the object performs on itself. Some common methods are close, delete, edit, and requery. Intelli-Sense or Auto Object Member list indicate Set property Run method Properties Methods method and properties by using a different icon. Methods can be used in VBA However, methods cannot be used in expressions.

40 7.9 OBJECT METHODS 132 Using a form method: Forms![frm_Customer].Requery When calling a method with arguments, use the following syntax: Object.method [(] argumentlist [)] If the method returns no result no parentheses are needed around the argument list. If a result is returned the argument list must be enclosed in parentheses.

41 7.9 OBJECT METHODS 133 When a method returns a result, you may assign it into a variable. Make sure to declare the variable correctly.

42 7.9 OBJECT METHODS 134 Arguments can be also passed as named Arguments Some common methods:

43 7.9 OBJECT METHODS 135

44 7.10 USING THE OBJECT BROWSER 136 Project/Library Box Search Box Classes List Search Result List Members of List Details Pane