PRB: "For Each" Behavior on Dynamically Changing Control Array (129450)


The information in this article applies to:

  • Microsoft Visual Basic Standard Edition, 32-bit, for Windows 4.0
  • Microsoft Visual Basic Professional Edition, 16-bit, for Windows 4.0
  • Microsoft Visual Basic Professional Edition, 32-bit, for Windows 4.0
  • Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows 4.0
  • Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows 4.0
This article was previously published under Q129450

SYMPTOMS

When using "For Each" to iterate through the elements of a control array that changes dynamically during the execution of the loop, the following unexpected behavior may occur:

  • Elements added after the For Each is started are not visited during its execution.
  • Elements deleted after the For Each is started are visited and generate error 340:
    Control array element 'n' doesn't exist.

CAUSE

The set of items (to be iterated over by the For Each) is set at the beginning of the iteration. Items added or deleted during the iteration do not affect the set of items iterated over.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

  1. Start a new project in Visual Basic. Form1 is created by default.
  2. Add a Command button (Command1) to your form.
  3. Set the Index property of Command1 to 0 (zero). This will create a control array with one element. You then refer to your control as Command1(0).
  4. Add the following code to the Form_Click event of Form1. 
          Sub Form_Click()
         On Error GoTo ErrorHandler
         Load Command1(1)
         Load Command1(2)
         Load Command1(3)

         For Each Elt In Command1
            Print "This is Command1("; Elt.Index; ")"
            If Elt.Index = 0 Then
               Unload Command1(2)
               Load Command1(4)
            End If

      SkipToHereOnError:
         Next
         Exit Sub

      ErrorHandler:
         Print Error$
         Resume SkipToHereOnError
      End Sub
  5. Start the program by choosing Start from the Run (or press the F5 key).
  6. Click Form1 to run the code in the Click event.
The following will be printed on Form1:

This is Command1(0)
This is Command1(1)
Control array element '2' doesn't exist
This is Command1(3)

NOTE: Attempting to access Command1(2) generates an error because it is unloaded at the first iteration of the loop, and that Command1(4) is not printed.
Modification Type:MajorLast Reviewed:12/9/2003
Keywords:kbprb KB129450
©2003 Microsoft Corporation. All rights reserved.