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I have a borderless WPF window (WindowStyle="None") that can be moved by catching LeftMouseDown and then call DragMove. That works fine.

However, I want to prevent any part of the window from leaving the screen area. I catch the LocationChanged but that is called AFTER the window has already moved and thus any changes to the windows position I make in that event cause the window to jump back, which looks very unprofessional.

Is there an event I can catch that is fired BEFORE the window is actually moved. I tried MouseMove and PreviewMouseMove but they don't get fired during DragMove.

This stuff works fine with WinForms.

Does anybody have a solution for this or is this just due to the half-baked nature and state of WPF?

H.B.
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Harald
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2 Answers2

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I didn't get the CoerceValueCallback approach to work (if anybody has a solution for this approach please share it).

My solution: Intercept WM_WINDOWPOSCHANGING message in a WPF WndProc. The solution is a bit long to post here, but here are 2 links that put me on the right track:

How to handle WndProc messages in WPF? (There were a few nay-sayers in this link that stated that WndProc would not work with WPF. I can't comment on the statement in that general fashion but in this particular case it works like a charm.)

http://huddledmasses.org/wpf-windows-that-snap-to-screen-edges/

Put body of OnPreviewPositionChange in WndProc.

Community
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Harald
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This stuff works fine with WinForms

Yes, but on the other hand, WinForms doesn't have DragMove... You could try to do it the same way as in WinForms, by handling MouseMove and moving the window yourself.

Another option would be to override the metadata for the Top and Left dependency properties with a CoerceValueCallback to prevent the window from leaving the screen. Not sure if that would work, though...

Thomas Levesque
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