1. VBA Modules, Functions, Variables, and Constants
Chapter 7
VBA Modules, Functions, Variables, and Constants

2. Chapter Objectives
Design VBA code that is organized into standard modules, independent class modules, and form and report class modules
Determine when each type of module is appropriate
Develop simple sub procedures, functions, and property procedures

3. Chapter Objectives
Determine when a sub procedure or a function is most appropriate
Declare arguments, variables, and constants
Invoke procedures and pass arguments between procedures
Cancel and manage events through VBA

4. Modules Procedure Module
Collection of VBA statements combined in a manner to accomplish a processing task
Module
Group of procedures related to a specific process
Makes maintaining the application easier in the long run

5. Modules Form and report class modules
Include code for all event procedures triggered by events occurring on a specific form or report, or the controls on that form or report
Figure 7-1 Procedures within modules

6. Modules Standard module Independent class modules
Module you can place sub and function procedures and declarations in to make available to other procedures throughout your application
Procedures can be executed whenever the application is running
Independent class modules
Not connected to a form or report
Procedures inside an independent class module can be executed as long as the application is open

7. Selecting Module Types
Selection of the best module type for a procedure depends on:
Runtime efficiency of the application
Amount of primary memory expected on the computer executing the application
Number of forms and reports that use a procedure

8. Selecting Module Types
Standard modules and independent class modules are loaded into primary memory when an application opens
Use primary memory even when they are not needed, yet the time needed to load the module occurs once
Form and class modules are loaded into primary memory when the form or report opens
Do not use memory until form or report is opened, but the form or report takes longer to open because module must be loaded

9. Sub Procedures Sub procedures Containers for programming code
Invoked at any time by writing a statement within a different procedure to invoke the necessary sub procedure
Place its name, and if needed, the values for its arguments on a line within the invoking procedure

10. Functions Functions Return values
Invoked by placing it in an expression or using it as a value to display in a control
Application can use the value returned by a function in the expression

11. Property Procedures Property procedure
Defines a property that is attached to an object through dot notation
Activated by assigning or using the value of a property
Used if the procedure will correspond to something that could be a property

12. Creating and Using Sub Procedures
Table 7-1 Data types in VBA and their corresponding types in Access tables

13. Creating and Using Sub Procedures
Table 7-1 Data types in VBA and their corresponding types in Access tables (continued)

14. Passing Arguments by Reference and by Value
When arguments are processed by reference:
The memory address containing the value to be used is “referenced” by the argument
When arguments are processed by value:
A copy of the value, instead of a reference to the memory location containing the value, is supplied to the procedure

15. Optional Keyword Optional keyword Named arguments approach
Can be used with arguments
Specifies that the invoking procedure does not need to provide a value for the argument
Named arguments approach
Arguments can be placed in any order and commas do not have to be used to represent blank arguments

16. Nuances of Argument Use
A procedure must be invoked using the same number of actual arguments as formal arguments in the sub statement, unless optional arguments are used
The actual arguments will supply values for the formal arguments in the order in which they are listed, so the data types must be compatible

17. Event Procedure Arguments
Event procedures
Special types of sub procedures located in form and report class modules
Most do not take arguments, but some have one or more predefined arguments
Flags
Arguments that contain values that Access evaluates during and after the procedure executes to determine how to continue the application’s processing

18. Event Procedure Arguments
Table 7-2 Event procedures with single arguments

19. Event Procedure Arguments
Intrinsic constants
Represent the legal values for arguments that specify actions other than canceling events
True
Intrinsic constant that represents value –1

20. Event Procedure Arguments
Table 7-3 Event procedure with multiple or special arguments

21. Event Procedure Arguments
Table 7-3 Event procedure with multiple or special arguments (continued)

22. Creating and Using Functions
Function Procedures
Similar to sub procedures
Use formal arguments, can be declared as Public or Private
Can contain variable and constant declaration statements
In a function procedure, the function is assigned a value
Assignment is fundamental difference between sub procedures and functions

23. Property Procedures – Let, Set, and Get
Property Let and Set procedures
Accept information from an invoking procedure, but do not return a value
Property Get procedures
Returns a value to the calling procedure
Property Let and Get usually appear in pairs

24. Property Procedures – Let, Set, and Get
Figure 7-2 Property procedures for frmIDSearchWindow

25. Declaring Variables Dim Statements
Define variables that will be used within procedures
Variables are frequently used to store immediate results as execution of the procedure moves from one line to another

26. Declaring Variables
Figure 7-3 Part of txtPaymentNo_BeforeUpdate in frmProcessPayment

27. Declaring Variables Private Public
Used in the Declarations section of a module to declare variables that are used only within the procedure contained by the module
Public
Used in the Declarations section to declare variables that can be used by any procedure in any module

28. Declaring Variables Static
Used in a procedure to declare variables that retain their value even after the procedure finishes executing
May be declared only within procedures

29. The Variant Data Type Variant data type VarType built-in function
Can contain almost any type of data, including numbers, strings, and dates
Only data type in VBA that can store null and empty values
VarType built-in function
Used to determine the type of data stored in a Variant

30. The Variant Data Type
Table 7-4 Values returned by VarType and variable testing functions

31. The User-Defined Type
VBA provides a way to create a user-defined type with a Type statement
Allows you to define a complex data structure
Useful when the values of many similar variables need to be copied to other variables

32. Single- and Multiple- Dimension Arrays
Collections of variables given a single name but indexed by one or more values
Array indexes begin at zero
ReDim statement
Can change the size of the array

33. Scope, Life, and the Dim Statement
Where and how variables are declared determine which other procedures can use the variable
Scope of a variable
How long the variable actually exists
Life of a variable

34. Scope, Life, and the Dim Statement
Table 7-5 Variable and constant scope prefixes

35. Scope, Life, and the Dim Statement
Figure 7-4 Procedure that facilitates the reuse of values

36. Scope, Life, and the Dim Statement
Any variable declared in the Declarations section of a module maintains its stored value as long as:
The application continues to run or
The form or report remains open
Variables declared with the Dim statement in a procedure are available to that procedure only as long as the procedure is running

37. Scope, Life, and the Static Statement
Variables declared with the Static statement in a procedure continue to exist after the procedure finishes
Programmers frequently use static variables to determine whether a newly entered value is the same as a previous value

38. Intrinsic and Symbolic Constants
Named item that retains the same value throughout the execution of a program
Intrinsic constant
Integer values that have some particular meaning
Makes programming easier for the developer and facilitates program maintenance

39. Intrinsic and Symbolic Constants
Constant that is defined by the programmer
Retains a constant value throughout the execution of a procedure
Similar to a variable except that its value is specified as soon as the constant is declared

40. Intrinsic and Symbolic Constants
Figure 7-5 Public constants in the Declarations section of the basUtilities module

41. Controlling Processing in the Declarations Section
Option Compare statement
Automatically included in Declarations section
Defines the default method to use when comparing text data
Three types of methods used when comparing text data:
Binary method
Comparisons will be case-sensitive

42. Controlling Processing in the Declarations Section
Three types of methods used when comparing text data (continued):
Text method
Comparisons will not be case sensitive
Database method
Comparisons are based on character’s relative positions according to the sort order specified when the database was created or compacted

43. Controlling Processing in the Declarations Section
If the Declarations section of the module containing the procedure contains an Option Explicit statement:
Variables must be explicitly defined prior to their use
If it does not:
Variables do not need to be declared before they are used

44. Chapter Summary
VBA statements are written inside functions procedures, sub procedures, and property procedures
Standard modules
Contain functions and sub procedures
Loaded into memory as soon as the application opens
Form and Report class modules
Contain all three types of procedures

45. Chapter Summary Functions differ from sub procedures in two ways
A function returns a value
A function has an associated data type
Functions should be written in cases where a value is being returned

46. Chapter Summary All procedures have arguments
Argument values can be passed
by reference
Changes made to the value passed into the procedure are reflected in the environment where the procedure was originally invoked
by value
Make a copy of the actual argument value available to the procedure

47. Chapter Summary Variables Can be local or they can be public
Usually only available while the code in which they have been declared is executing
Deleted from memory unless they have been declared as static
May be declared as one of a number of different data types

48. Chapter Summary Arrays Constants
Collections of indexed variables with a common name, and user defined types, which allow programmers to create their own data structures
Constants
Help make the program code more understandable