Question

I’m working on a windows application where I’m implementing the whole event loop and everything like that myself (there’s a reason for that). In one place, I need to execute some code AFTER a window is shown. Normally, when the window is created, I do some initialisation when WM_CREATE message is received. WM_SHOWWINDOW is sent just BEFORE the window is displayed. However I need to get some code executed right AFTER the window is displayed for the first time. I can’t seem to find a notification message sent AFTER the window is shown. Could it be that there isn’t one?

Of course, I can keep a boolean – FirstRun – indicating whether or not I had performed my logic, and then execute the code when WM_ACTIVATE is received, provided the boolean is TRUE, then set FirstRun to FALSE so that the code is not execute the next time I am receive WM_ACTIVATE, but this seems somewhat unnatural to me.

It’s been ages since I did win32 programming on this level, so can’t remember much of it. What is the best approach here?

Answer 1

There is no special notification, but in many cases you can use this trick:

LRESULT CALLBACK MainWndProc(
HWND hwnd,        // handle to window
UINT uMsg,        // message identifier
WPARAM wParam,    // first message parameter
LPARAM lParam)    // second message parameter
{ 
switch (uMsg) 
{ 
    case WM_USER + 100:
        //window is just displayed, do some actions
        return DefWindowProc(hwnd, uMsg, wParam, lParam); 
    case WM_CREATE:
        PostMessage(hwnd, WM_USER + 100, 0, 0);
        return DefWindowProc(hwnd, uMsg, wParam, lParam);
    default: 
        return DefWindowProc(hwnd, uMsg, wParam, lParam); 
}
return 0;
}