How To Use One IsDialogMessage() Call for Many Modeless Dialogs (71450)

SUMMARY

In the Windows environment, an application can implement more than one modeless dialog box with a single call to the IsDialogMessage() function. This can be done by using the following three-step method:

Maintain the window handle to the currently active modeless dialog box in a global variable.
Pass the global variable as the hDlg parameter to the IsDialogMessage() function, which is normally called from the application's main message loop.
Update the global variable whenever a modeless dialog box's window procedure receives a WM_ACTIVATE message, as follows:
- If the dialog is losing activation (wParam is 0), set the global variable to NULL.
- If the dialog is becoming active (wParam is 1 or 2), set the global variable to the dialog's window handle.

MORE INFORMATION

The information below demonstrates how to implement this technique.

Declare a global variable for the modeless dialog box's window handle as follows:
```
      HWND hDlgCurrent = NULL;

					
```

In the application's main message loop, add a call to the IsDialogMessage() function as follows:

      while (GetMessage(&msg, NULL, 0, 0))
         {
         if (NULL == hDlgCurrent || !IsDialogMessage(hDlgCurrent, &msg))
            {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
            }
         }

In the modeless dialog box's window procedure, process the WM_ACTIVATE message as follows:

      switch (message)
         {
         case WM_ACTIVATE:
            if (0 == wParam)             // becoming inactive
               hDlgCurrent = NULL;
            else                         // becoming active
               hDlgCurrent = hDlg;

            return FALSE;
         }

For more information on the WM_ACTIVATE message, see page 6-47 in "Microsoft Windows Software Development Kit Reference Volume 1" for the Windows SDK version 3.0 and page 87 of "Programmer's Reference, Volume 3: Messages, Structures, and Macros" for the Windows SDK version 3.1.

For details on the IsDialogMessage() function, see page 4-266 in "Windows Software Development Kit Reference Volume 1" for the Windows SDK version 3.0 and page 553 of "Programmer's Reference, Volume 2: Functions" for the Windows SDK version 3.1.

For details on using a modeless dialog box in an application for the Windows environment, see Chapter 10 of "Programming Windows," second edition, (Microsoft Press) written by Charles Petzold.