[python-win32] Custom control, WS_CHILD

[Henry Baxter]

Problem solved!

I was using ctypes.byref to pass a reference to the window class, but before
calling CreateWindow the window class in question went out of scope and was
destroyed.

I'm worried this type of problem will happen more often, but I'm not sure
how to stop it...suggestions welcome!


Henry

On Jan 12, 2008 1:42 AM, Henry Baxter <henry.baxter at gmail.com> wrote:

> Hello,
>
> I have been doing some win32 programming using ctypes. I have successfully
> created windows, common controls, manipulated and shown images, and so
> forth. However, I am having trouble with custom controls.
>
> I can create a new window class, successfully register it, then
> successfully create a child window.
>
> When the parent window gets the UpdateWindow call, the program crashes. If
> I set the style of the child to not include WS_VISIBLE, the program does not
> crash, but the window of course does not appear. If I then call ShowWindow
> on the child window, the program crashes.
>
> I have carefully monitored the windows messages that are being seen by the
> main window's procedure and the child window's procedure, and the crash
> always happens right after the first WM_PAINT to the parent window. No
> further messages are seen by either procedure before it crashes. Before the
> crash both procedures process normal messages like WM_CREATE etc.
>
>
> Backing up a step, I started from scratch with a main window and a normal
> child button control, made sure it worked fine, then used SetWindowLong to
> replace the window procedure on the child control. This works fine as long
> as I don't replace the window procedure too early - if I replace it before
> the first call to UpdateWindow in the startup procedure of the application,
> the program once again crashes (and I really do believe these two problems
> are related).
>
>
> Basically, it seems that I am missing something vital from my windows
> procedure that has something to do with the window being a WS_CHILD, and to
> do with creation or painting. The system's button window procedure has it,
> and my main window doesn't need it, but my custom child control does.
>
> For testing purposes I call DefWindowProc with the appropriate arguments,
> and don't do anything else in the child window's procedure. Is there
> something else I need to do though?
>
>
>
> I'm really stuck, really confused. Any suggestions?
>
>
>
> --
> Henry
>
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