The dangers of messing with activation when handling a WM_ACTIVATE message

Raymond Chen

This is basically the same thing as The dangers of playing focus games when handling a WM_KILLFOCUS message, just with activation in place of focus. One developer discovered the hard way that if you mess with activation inside your WM_ACTIVATE handler, things get weird. The author noted that if he posted a message and did the work from the posted message, then everything came out okay.

A follow-up to the original message noted that passing the SWP_NOACTIVATE flag to the SetWindowPos function solves the problem. Do you understand why?

Raymond Chen

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