Preserving the Undo List

As you are working in Excel, there is a bit of a "safety net" in place in regards to changes you make. Most people know that if they mess things up, they can quickly press Ctrl+Z or choose the Undo command from the Edit menu or by using the Undo tool on the toolbar. If you don't like what you just did, you can easily undo it and get back to the way things were before.

When you run a macro, however, the macro doesn't "play nice" with the Undo list. In fact, running a macro completely erases the Undo list, and therefore you cannot automatically undo the effects of running the macro. There is no intrinsic command—in Excel or in VBA—to preserve the Undo list. There are a couple of ways that you can approach the problem, however.

If you feel that you might want to undo the effects of a macro, the first thing you can do is to save your workbook before running the macro. This, in effect, gives you a "pre-macro" version of the workbook. If you want to later revert to this version, simply close the workbook without saving and then reload it from disk.

Another option is to rethink the way you do your macros. If you have a macro that does a lot of processing of information in your worksheet, code the macro so that it maintains, in memory, the state of anything that it changes. You can then create a separate macro that reads this information and effectively undoes the effects of the first macro.

To make this approach really handy, the last step in your primary macro can be to "stuff" information on the Undo stack. This info can then be used, but the user, to "undo" macro that you created. For instance, the following macro command could be the last one in your primary macro:

Application.OnUndo "Primary Macro", "UndoPrimary"

After this command, when the user looks at the Undo list, he or she will see the text "Primary Macro." If they choose this option from the Undo list, then your "undo" macro (UndoPrimary) is executed.

You should note that this approach doesn't save what was on the Undo list before you ran the macro—there seems no way to do that. When your primary macro is through running, there will only be a single option available on the Undo list: Primary Macro.