WM_ENTERSIZEMOVE / WM_EXITSIZEMOVE - when using menu, not always paired

Question

To prevent my application changing the window content while user is moving its window around, I capture messages WM_ENTERSIZEMOVE / WM_EXITSIZEMOVE and I pause the application between the messages. However, sometimes it happens I receive WM_ENTERSIZEMOVE but no WM_EXITSIZEMOVE at all. One repro is:

• open the window menu
• click on Size
• do not resize the window, rather click into the window

Notice the window never received any WM_EXITSIZEMOVE.

When checking how this works, I have also checked Microsoft DirectX sample and I have noticed the same problem. Once you follow the repro steps above, the sample application looks frozen (I have tried it just now with BasicHLSL sample from March 2009 SDK).

How is the application expected to respond to this? Are there some other conditions which should terminate the "moving or sizing modal loop"?

Answer 1

I know this is rather late, but it might still help you - and it is likely to help others who find it in a search, like I did.

It seems that in the situation you mentioned, the WM_CAPTURECHANGED message is sent when the resizing is "cancelled". After extensive testing it seems that this is always sent just before WM_EXITSIZEMOVE is (or should be!), and at no other stage between WM_ENTERSIZEMOVE / WM_EXITSIZEMOVE.

The WM_CAPTURECHANGED message is sent at various other times too, so you should only react to it if a WM_ENTERSIZEMOVE message has been sent, but the following WM_EXITSIZEMOVE hasn't.