C++ - Dialog box question

Question

This is a more concrete question that is connected with my previous one.

I have an application that uses a timer. The code is written the way the my WM_TIMER handler call a DialogBoxParam(...) with some custom message handler (let's call it DlgProc ).

This is done somewhat the following way:

case WM_TIMER: { // Routine, that displays a special message box DisplayMessageBox(...); return 0; }

Now, if I make DlgProc handle the messages like this (see the code), this would result in tons of dialog boxes (one per WM_TIMER call).

   switch (msg)
   {
   case WM_INITDIALOG:
      // (...)
      return TRUE;
   case WM_COMMAND:
      // (...)
      return TRUE;
   return FALSE;
   }

But if I add a dummy WM_PAINT handler ( return TRUE; ) to my DlgProc , this results in exactly one shown DialogBox and 100% CPU load (that's because I receive tons of WM_PAINT messages).

Q:

What can be done here if I want my application to show exactly ONE dialog box and have no CPU load for WM_PAINT processing? (I mean like, have behaviour similiar to draw unique dialog box and fully pause the parent window) .

Also it would be great if someone explains what actually happens in this situation and why do I receive gazillions of WM_PAINT messages to my dialog box and why their processing (with return TRUE ) results in preventing the other dialog boxes creation.

Thank you.

Answer 1

1) You should disable the timer after the first WM_TIMER signal is caught if you want to show only one single dialog box. You can do this using KillTimer() .

2) Windows wants to keep the GUI up-to-date. Whenever a region on the screen should be updated, it is invalidated using InvalidateRect or InvalidateRgn. Now, for every "invalid" screen part, WM_PAINT is called in order to make in "valid" again.

If you don't do it (or just parts of it), Windows will call WM_PAINT again ... and again. One way is to call ValidateRect . In many cases BeginPaint() and EndPaint() are used to do the job.

3) Maybe most important: you should not just return FALSE! Try DefWindowProc() for windows and DefDlgProc() for dialogs. They will also take care of WM_PAINT appropriately.

Answer 2

不是您注册了WM_PAINT，而是一定要引起它（即使您没有添加WM_PAINT：处理程序），也要查找重新绘制函数（例如InvalidateRect（））