VB6 Tip: Best practices requires that you ensure all forms unload

by Peter Aitken | Jan 14, 2005 8:00:00 AM

Tags: Microsoft development tools, Programming languages, Peter Aitken, Microsoft Visual Basic 6.0, Peter Aitken, Microsoft Visual Basic, main form, Visual Basic Tips Newsletter

Takeaway: Writing proper code requires that when a VB program ends, all of its forms will be unloaded and removed from memory.

When a Visual Basic 6 program ends, all of its forms should be unloaded and removed from memory. VB doesn't do this automatically; therefore, if your program contains a lot of forms, it's possible for one or more forms to remain in memory even after the program terminates.

Calling a form's Hide method or setting its Visible property to False doesn't unload it. Even if you explicitly unload a form (using the Unload procedure), it can still take up resources—unless the form's reference is set to Nothing. This tip shows how to ensure that all of the forms in a program unload and that their resources release upon program termination.

This technique makes use of the fact that a VB application has a global Forms collection whose elements represent all of the application's loaded forms.

You could loop through this collection, unloading all forms as shown in this code snippet:

Dim f As Form
For Each f In Forms
  Unload f
  Set f = Nothing
Next f

There's a problem with this straightforward approach: If you execute this code from a procedure, it works fine; but if you call it from the main form's Form_Unload event procedure, it will try to unload the main form, which is already in the process of unloading itself (otherwise the Form_Unload event procedure wouldn't have fired). Here's how you can get around this potential problem:

Public Sub UnloadAllForms(Optional FormToIgnore _
  As String = "")

  Dim f As Form
  For Each f In Forms
    If f.Name <> FormToIgnore Then
      Unload f
      Set f = Nothing
    End If
  Next f
   
End Sub

With this procedure in place, you'd call it like this from the main form's Form_Unload event procedure:

UnloadAllFormsMe.Name

It will unload all forms except the main form.

If calling it from a separate procedure, don't pass an argument, and the procedure will unload all of the program's forms.

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ensure all forms unloademmbe1@...  | 01/17/05

Unloading all forms?HenryStinson@...  | 01/21/05

Forms collection misapprehensionjohnwm  | 03/25/05

Is Nothing can cause Problems tooismith@...  | 04/13/07

Unloading formsae@...  | 11/04/05

Bad coding practice to begin withjreddy@...  | 02/01/07