Attempted to Read or Write Protected Memory

I’ve been working on switching over to a “new” machine (more on that in a new post). In the process my time card program stopped working with the following error:

System.AccessViolationException was unhandled Message: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

Unfortunately this error doesn’t show up until well after it occurs. So you need to make some educated guesses as to where it is coming from. So what I did is I just commented out code one at a time in the procedure where it was originating from. The code that was shown to be problematic was called from two different places - so the error occurred only from one of the branches but not the other. So that was a bit confusing. It was also confusing because it didn’t happen on my Windows XP computer, just on the “new” Windows 8 computer.

Eventually I figured out (with help from StackOverflow) that it was caused by changing the values of my drop down list during the click event of the combo box.

To fix the problem, Microsoft recommends that you don’t change the values of the combo box during the event. So, I added a timer component to the form. The timer allows you to call a function in the future after completing other operations. I also use a timer in the Scribble Filter preview box when someone selects multiple lines on the form - so Excel doesn’t go crazy will I’m selected the corresponding rows.

Tue Feb 12, 2013 | tags: fail error windows-forms async

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