DOCUMENT:Q190043  07-AUG-1998  [vbwin]
TITLE   :PRB: Controls Collection vs. Standard Collection in For Each
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:WINDOWS:6.0;
OPER/SYS:WINDOWS
KEYWORDS:kbVBp600 kbnokeyword

======================================================================
---------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Visual Basic Learning, Professional, and Enterprise Editions
   for Windows, version 6.0
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SYMPTOMS
========

When you remove controls from a Control collection in a For...Each loop,
you might receive the following error:

   Runtime error 735: The control is no longer usable because it has been
   removed from the control collection.

This occurs when you try to access the properties/methods of a control
within the same loop that you are using to remove it from the collection.

CAUSE
=====

When you remove an element from a standard VBA Collection object inside a
loop, the iterator is updated automatically. Consequently, the collection
is aware that the element has been removed, and will not attempt to access
that member after it has been removed. The Controls collection for the
Visual Basic Form object does not exhibit this behavior, and will fail with
Runtime error 735 if you attempt to access the properties/methods of a
control after it has been removed from the collection.

RESOLUTION
==========

To avoid Runtime error 735, do one of the following:

 - Remove the unwanted item(s) from the Collection before iterating over
   it.

 - Use two separate iterations. One to remove the unnecessary elements, and
   the other to access the collection elements. See step 4 in the MORE
   INFORMATION section of this article for an example.

STATUS
======

This behavior is by design.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Start a new Standard EXE project in Visual Basic.

2. Copy the following code to the code module for Form1.

      Private Sub Form_Load()
         Dim x As Control
         Dim y As Boolean

         Controls.Add "vb.commandbutton", "a"
         Controls.Add "vb.commandbutton", "b"
         Controls.Add "vb.commandbutton", "c"
         Controls.Add "vb.commandbutton", "d"
         Controls.Add "vb.commandbutton", "e"
         Controls.Add "vb.commandbutton", "f"
         For Each x In Controls
            Select Case x.Name
               Case "d", "e", "f"
               Controls.Remove x
            End Select
         Debug.Print x.Name
         Next
         End Sub

3. Run the project. Runtime error 735 occurs.

4. Replace the code from step 2 with the following code.
   NOTE: This code uses two separate iterations to accomplish the task.
   Because you can remove Control Collection elements by name, another
   alternative is to remove the controls without using a loop.

      Private Sub Form_Load()
         Dim x As Control
         Dim y As Boolean

         Controls.Add "vb.commandbutton", "a"
         Controls.Add "vb.commandbutton", "b"
         Controls.Add "vb.commandbutton", "c"
         Controls.Add "vb.commandbutton", "d"
         Controls.Add "vb.commandbutton", "e"
         Controls.Add "vb.commandbutton", "f"
         For Each x In Controls
            Select Case x.Name
               Case "d", "e", "f"
               Controls.Remove x
            End Select
         Next
         For Each x In Controls
            Debug.Print x.Name
         Next

      End Sub

5. Run the project.

RESULT: The names of the remaining controls appear in the Immediate window.

Additional query words:
======================================================================
Keywords          : kbVBp600 kbnokeyword
Version           : WINDOWS:6.0;
Platform          : WINDOWS
Issue type        : kbprb

=============================================================================

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