Why does my form sometimes vanish when closing a dialog?

Question

Occasionally, seemingly randomly, when I close a dialog form my main form seems to move back in the window order, disappearing behind the next application back (usually Visual Studio). It retains focus, so clicking it in the taskbar minimises it, requiring another click. Whenever this happens, the control colours seem to change a little as well, but revert if I maximise and restore the window.

Any idea why this happens?

Edit: This happens when I'm debugging; it might happen at runtime too, but I usually don't have anything behind the application then, so I haven't noticed. Nobody has mentioned it.

Answer 1

This will happen when the dialog closes and Windows cannot find any window in your app that isn't disabled. Forced to move the focus somewhere, it will pick a window of another app to give the focus to. Your form will disappear behind it.

Exactly why your main form is disabled when this happens isn't clear. The color change certainly suggests you are changing the Enabled property of the form. Everything turns battle-ship gray when you do that. Setting Enabled back to true after the dialog closes doesn't work, it's too late. Just don't tinker with Enabled, the ShowDialog() method already disables other windows.