PRB: "For Each" Behavior on Dynamically Changing Control Array

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

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.

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