CODEWITHSUNDEEP
winapix86-64windows64
Steve Valliere
Steve Valliere

Reputation: 1207

No WM_SIZE received when windows resized

I have a fairly simple windows program that created a listview control that should exactly fill the client area. That works at start up, and I think will work if the window is resized --- except the windows NEVER receives any WM_SIZE messages (after the initial one sent on window creation.) I verified this using Spy++x64 as an administrator to ensure I was capturing everything. Spy++ showed the window receiving WM_SIZING, WM_WINPOSCHANGED, WM_NCCALCSIZE, and WM_WINPOSCHANGING (this list isn't in any particular order) but NEVER a WM_SIZE.

This is a 64-bit program, but I don't know why that should matter.

So, is there something I could have done that allows the window to be completely resizable, but prevent Windows from ever generating WM_SIZE messages when that happens? If not, is there something I need to do (that was never needed in the past 30 years) to let Windows know I need to see those WM_SIZE events?

Upvotes: 3

Views: 1318

Answers (1)

Steve Valliere
Steve Valliere

Reputation: 1207

It turns out that the default window procedure generates the WM_SIZE when it processed WM_WINDOWPOSCHANGED and, since I was handling WM_WINDOWPOSCHANGED, no size messages were created. So I forwarded the position changed message to the default handler and the messages are back.

This follows documented behavior. There's a remark in the documentation for the WM_WINDOWPOSCHANGED documentation:

By default, the DefWindowProc function sends the WM_SIZE and WM_MOVE messages to the window. The WM_SIZE and WM_MOVE messages are not sent if an application handles the WM_WINDOWPOSCHANGED message without calling DefWindowProc. It is more efficient to perform any move or size change processing during the WM_WINDOWPOSCHANGED message without calling DefWindowProc.

Yup, I'm sorry to admit that I failed to read the documentation for all of the Window messages that I was NOT having problems with when I needed to find out about WM_SIZE. Silly me for not assuming the documentation I needed about WM_SIZE was only to be found under some other message! All it says about the message generation in the WM_SIZE documentation is:

Sent to a window after its size has changed.

There is no mention AT ALL of any dependency on the default processing for a DIFFERENT message to be found. Ergo, the behavior is effectively undocumented, especially since it may be critical information, as it was for me.

Oh well, I give up, this place has become far too much of just smacking people down for asking questions some people think are too easily answered. Try to remember that not everyone has an eidetic memory and access to all of the documentation you have all memorized. Some of us look up the thing we're working on and expect to find the important details about it. THEY ARE NOT PRESENT. Bye!

Upvotes: 2

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