MS-Access / Getting Started

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Dim Statement

Use a Dim statement in the Declarations section of a module to declare a variable or a variable array that can be used in all procedures in the module. Use a Dim statement within a procedure to declare a variable used only in that procedure.

Syntax

Dim {[WithEvents] variablename
  [([<array dimension>],... )] [As [New]
  datatype]},...

where <array dimension> is

[lowerbound To ] upperbound

Notes

If you do not include an <array dimension> specification but you do include the parentheses, you must include a ReDim statement in eac procedure that uses the array to dynamically allocate the array at run time. You can define an array with as many as 60 dimensions. If you do not include a lowerbound value in an <array dimension> specification, the default lower bound is 0. You can reset the default lower bound to 1 by including an Option Base 1 statement in the module Declarations section. The lowerbound and upperbound values must be integers, and upperbound must be greater than or equal to lowerbound. The number of members of an array is limited only by the amount of memory on your computer.

Valid datatype entries are Byte, Boolean, Integer, Long, Currency, Single, Double, Date, String (for variable-length strings), String * length (for fixed-length strings), Object, Variant, or one of the object types described earlier in this tutorial. You can also declare a userdefined variable structure using the Type statement and then use the user type name as a data type. You should always explicitly declare the data type of your variables. If you do not include the As datatype clause, Visual Basic assigns the Variant data type.

Use the New keyword to indicate that a declared object variable is a new instance of an object that doesn't have to be set before you use it. You can use the New keyword only with object variables to create a new instance of that class of object without requiring a Set statement. You can't use New to declare dependent objects. If you do not use the New keyword, you cannot reference the object or any of its properties or methods until you set the variable to an object using a Set statement.

Use the WithEvents keyword to indicate an object variable within a class module that responds to events triggered by an ActiveX object. Form and report modules that respond to events on the related form and report objects are class modules. You can also define custom class modules to create custom objects. If you use the WithEvents keyword, you cannot use the New keyword.

Visual Basic initializes declared variables at compile time. Numeric variables are initialized to zero (0), variant variables are initialized to empty, variable-length string variables are initialized as zero-length strings, and fixed-length string variables are filled with American National Standards Institute (ANSI) zeros (Chr(0)). If you use a Dim statement within a procedure to declare variables, Visual Basic reinitializes the variables each time you run the procedure.

Examples

To declare a variable named intMyInteger as an integer, enter the following:

Dim intMyInteger As Integer

To declare a variable named dbMyDatabase as a database object, enter the following:

Dim dbMyDatabase As Database

To declare an array named strMyString that contains fixed-length strings that are 20 characters long and contains 50 entries from 51 through 100, enter the following:

Dim strMyString(51 To 100) As String * 20

To declare a database variable, a new table variable, and two new field variables for the table; set up the objects; and append the new table to the Tabledefs collection, enter the following:

Public Sub NewTableExample()
    Dim db As DAO.Database
    Dim tdf As New DAO.TableDef, _
	fld1 As New DAO.Field, _
	fld2 As New DAO.Field
    ' Initialize the table name
    tdf.Name = "MyTable"
    ' Set the name of the first field
    fld1.Name = "MyField1"
    ' Set its data type
    fld1.Type = dbLong
    ' Append the first field to the Fields
    ' collection of the table
    tdf.Fields.Append fld1
    ' Set up the second field
    fld2.Name = "MyField2"
    fld2.Type = dbText
    fld2.Size = 20
    ' Append the second field to the table
    tdf.Fields.Append fld2
    ' Establish an object on the current database
    Set db = CurrentDb
    ' Create a new table by appending tdf to
    ' the Tabledefs collection of the database
    db.TableDefs.Append tdf
End Sub

To declare an object variable to respond to events in another class module, enter the following:

Option Explicit
Dim WithEvents objOtherClass As MyClass

Sub LoadClass ()
    Set objOtherClass = New MyClass
End Sub

Sub objOtherClass_Signal(ByVal strMsg As string)
    MsgBox "MyClass Signal event sent this " & _
	"message: " & strMsg
End Sub

In class module MyClass, enter the following:

Option Explicit
Public Event Signal(ByVal strMsg As String)

Public Sub RaiseSignal(ByVal strText As String)
    RaiseEvent Signal(strText)
End Sub

In any other module, execute the following statement:

MyClass.RaiseSignal "Hello"