INFO: Terminating the Creation of an MDI Child Window

• Microsoft Windows Software Development Kit (SDK) 3.1

SUMMARY

In an application designed with the Microsoft Windows Multiple Document Interface (MDI), there are situations in which it is desirable to destroy an MDI child window during the processing of its WM_CREATE message. For example, the design of the application may require terminating window creation if a memory allocation needed to hold data for an MDI child fails.

Unfortunately, returning -1 to end processing of the WM_CREATE message will not cleanly destroy the child window. Similarly, posting a WM_CLOSE message will cause the display to flash as the child is drawn, made active, and destroyed. This article describes a technique to avoid this unacceptable visual effect.

To avoid the flash, the application can clear the redraw flag for the MDI client window. This prevents the MDI client window and its children from painting. The remainder of this article contains code to implement this technique.

Before the application processes the MDI child window's WM_CREATE message, it does not change its display to reflect the new child window. If the application determines that it must abort creating the MDI child window at this time, it should clear the MDI client window's redraw flag and post a WM_CLOSE message to the child window. When the application processes the WM_DESTROY message, turn the redraw flag back on. The following code demonstrates these steps:

   case WM_CREATE:

    ...

       if (DestroyMePolitely)
           {
           SendMessage(hWndMDIClient, WM_SETREDRAW, FALSE, 0L);
           PostMessage(hWnd, WM_CLOSE, 0, 0L);
           }
       break;

   ...

   case WM_DESTROY:
       SendMessage(hWndMDIClient, WM_SETREDRAW, TRUE, 0L); 

Additional query words: 3.00 3.10

Keywords : kb16bitonly kbMDI kbSDKPlatform kbWndw
Version : WINDOWS:3.1
Platform : WINDOWS
Issue type : kbinfo