Aborting a Macro and Retaining Control

When you are developing a macro for others to use, you may want to add a method for the user to exit your macro before it ends, and still retain control of what the macro does. Ctrl+Break will stop a macro, but it doesn't exit gracefully, as it allows the user to view the code in the VBA Editor.

There are several ways you can approach this problem. The first is to build a "do you want to exit" prompt into your macro, and then have the macro display the prompt periodically. For instance, consider the following code:

Do ...

    '    your code goes here

    Counter = Counter + 1
    If Counter Mod 25 = 0 Then
        If MsgBox("Stop Macro?", vbYesNo) = vbYes Then End
    End If
Loop

The macro construction is based on the premise that you have a series of steps you want to repeat over and over again, through the use of a Do ... Loop structure. Every time through the loop, the value of Counter is incremented. Every 25 times through the loop, the "stop macro?" prompt is displayed, and the user has a chance to exit.

This approach is easy to implement and may work quite well for some purposes. The biggest drawback to this approach, however, is that it doesn't allow immediacy—the user must wait to exit the macro until at least 25 iterations have occurred.

Another approach is to "hide" the VBA code and apply a password to it. You do this by following these steps from within the VBA Editor:

1. Choose the VBAProject Properties option from the Tools menu. The editor displays the Project Properties dialog.
2. Make sure the Protection tab is displayed. (See Figure 1.)



Figure 1. The Protection tab of the Project Properties dialog box.

3. Choose the Lock Project for Viewing check box.
4. In the Password box, enter a password you want used to protect the macro.
5. In the Confirm Password box, enter the same password a second time.
6. Click OK.

Close the VBA Editor, then save the workbook. With the VBA project protected, the user can still click Ctrl+Break to stop the macro, but they won't be able to get to the actual program code. They will only be able to choose from the Continue or End buttons, both of which protect your code. As an added benefit, this approach also restricts the user from viewing your code by using menu, toolbar, or ribbon choices.

Perhaps the best approach, however, is to create an error handler that will essentially take charge whenever the user presses Esc or Ctrl+Break. The handler that is run can then ask the user if they really want to quit, and then shut down gracefully if they do. Here's some example code that shows how this is done:

Sub Looptest()
    Application.EnableCancelKey = xlErrorHandler
    On Error GoTo ErrHandler

    Dim x As Long
    Dim y As Long
    Dim lContinue As Long

    y = 100000000
    For x = 1 To y Step 1
    Next

    Application.EnableCancelKey = xlInterrupt
    Exit Sub

ErrHandler:
    If Err.Number = 18 Then
        lContinue = MsgBox(prompt:=Format(x / y, "0.0%") & _
          " complete" & vbCrLf & _
          "Do you want to Continue (YES)?" & vbCrLf & _
          "Do you want to QUIT? [Click NO]", _
          Buttons:=vbYesNo)
        If lContinue = vbYes Then
            Resume
        Else
            Application.EnableCancelKey = xlInterrupt
            MsgBox ("Program ended at your request")
            Exit Sub
        End If
    End If

    Application.EnableCancelKey = xlInterrupt
End Sub

Notice that this example uses the EnableCancelKey method, assigning it the name of the label that should be jumped to if the cancel key (Esc or Ctrl+Break) is pressed. In this case, ErrHandler is jumped to, and the user is asked what to do. If the user chooses to exit, then the macro is shut down gracefully.

Notice that the first thing done after the ErrHandler label is to check if the Number property of the Err object is equal to 18. If it is, you know that a cancel key was pressed. If not, then some other type of error occurred, and it should be handled in whatever way is appropriate for your macro.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (3021) applies to Microsoft Excel 97, 2000, 2002, and 2003. You can find a version of this tip for the ribbon interface of Excel (Excel 2007 and later) here: Aborting a Macro and Retaining Control.