Global Variables Access Visual Basic

Program-Wide Data Storage Tutorial

Global variables are a powerful feature in Microsoft Access. There are basically two classes these Visual Basic global variables.

• Local variables defined in a form instance, usually when the form opens.  These variables persist as long as the form remains open. These variables and constants are also known as Public Variables and Public Constants since they are known only to the form and subforms attached to a main form.
  
  

  New! Download Access example of Global Variables as Query Parameters

• Instance-wide variables persist for the duration of the Microsoft Access database session.  These variables, including global constants, are defined in association with a module and become active as soon as the module is called.

Here's an example of the Visual Basic code required to setup public form-level variables in a form:

Public gbl_previous_tab As String
Public gbl_username As String
Option Explicit

Private Sub Form_Open(Cancel As Integer)
    ' doing something here
End Sub

As this example show the declaration of a database global variable come right after the 'Option Compare Database' statement and before all declarations of (any) subroutines and functions within the form.

The definition of instance-wide Access global variables is carried out in a module.  The following is the code we use to initialize our Access global variables:

' Access global variables definition
Global GBL_Username As String
Global GBL_Previous_Tab As String

Option Explicit

Public Sub Init_Globals()
' Access global variable initialization
    GBL_Username = Environ("username")
    GBL_Previous_Tab = " "
End Sub

Then we make a call to the Init_Globals subroutine in our first-opening form as follows:

Option Explicit

Private Sub Form_Open(Cancel As Integer)
    DoCmd.Maximize
    Call Init_Globals
End Sub

As you can see there a lots of things you can keep track with Access global variables.  You can also do some neat tricks - like passing parameters to SQL queries using global variables.

Try our downloadable Access database demonstration of using Global variables as query parameters.

More Global Variable examples:

Access Database Security Alternative

initialize global variables Call set_globals ' Hide tabs Me.TabCtl0.Pages. ... set global access level to failsafe no access then lookup access level ... www.blueclaw-db.com/microsoft_access_security.htm