The Old New Thing

Modality, part 8: A timed MessageBox, the better version

March 4, 2005 Mar 4, 2005 03/4/05

Raymond Chen

A few days ago, we saw a simple version of a timed message box which had a limitation that it could be used from only one thread at a time. Today we'll work to remove that limitation. As you may recall, the reason why it could be used from only one thread at a time was that we kept the "Did the message box time out?" flag in a global. To ...

Modality, part 7: A timed MessageBox, the cheap version

March 1, 2005 Mar 1, 2005 03/1/05

Raymond Chen

As we noted at the end of part 3, now that you know the conventions surrounding the WM_QUIT message you can put them to your advantage. The more robust you want the TimedMessageBox function to be, the more work you need to do. Here's the cheap version, based on the sample in the Knowledge Base, but with some additional bug fixes...

Modality, part 6: Interacting with a program that has gone modal

February 28, 2005 Feb 28, 2005 02/28/05

Raymond Chen

Earlier we saw the importance of setting the right owner window for modal UI. It is also important, when manipulating a window, to respect its modality. For example, consider the program we ended up with last time, the one which calls the MessageBox function to display a modal dialog. If we wanted to get that program to exit and sent a ...

Modality, part 5: Setting the correct owner for modal UI

February 24, 2005 Feb 24, 2005 02/24/05

Raymond Chen

Here is the very simple fix for the buggy program we presented last time. void OnChar(HWND hwnd, TCHAR ch, int cRepeat) { switch (ch) { case ' ': MessageBox(hwnd, TEXT("Message"), TEXT("Title"), MB_OK); if (!IsWindow(hwnd)) MessageBeep(-1); break; } } We have fixed the problem by passing the correct owner window for the...

Modality, part 4: The importance of setting the correct owner for modal UI

February 23, 2005 Feb 23, 2005 02/23/05

Raymond Chen

If you decide to display some modal UI, it is important that you set the correct owner for that UI. If you fail to heed this rule, you will find yourself chasing some very strange bugs. Let's return to our scratch program and intentionally introduce a bug related to incorrect owner windows, so that we can see the consequences. void ...

Modality, part 3: The WM_QUIT message

February 22, 2005 Feb 22, 2005 02/22/05

Raymond Chen

After our two quick introductions to modality, we're now going to dig in a little deeper. The trick with modality is that when you call a modal function, the responsibility of message dispatch is handled by that function rather than by your main program. Consequently, if you have customized your main program's message pump, those ...

Modality, part 2: Code-modality vs UI-modality

February 21, 2005 Feb 21, 2005 02/21/05

Raymond Chen

Last time, we saw an example of code that was UI-modal but not code-modal. The opposite is also true: You can have code-modality without UI-modality. In fact, this is far more common than the UI-modal-but-not-code-modal scenario. You encounter modal loops without a visible change in UI state when you drag the scroll bar thumb, drag the window...

Modality, part 1: UI-modality vs code-modality

February 18, 2005 Feb 18, 2005 02/18/05

Raymond Chen

From the end-users' point of view, modality occurs when the users are locked into completing a task once it is begun, with the only escape being to cancel the entire operation. Opening a file is an example of a modal operation: Once the "Open" command has been selected, users have no choice but to select a file for opening (or to cancel the ...