About message-only windows
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Thread: About message-only windows

  1. #1

    About message-only windows

    I'm surprised how little information there is about message-only windows and the HWND_MESSAGE constant. I don't have Windows 2000 or XP, so I want someone to do the following.

    • List the steps necessary to reliably determine whether a window is a message-only window. (GetWindow, GetParent, etc.?)
    • Determine whether message-only windows can be enumerated using the EnumChildWindows function with HWND_MESSAGE as the first parameter.

  2. #2
    Join Date
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    You cannot enumerate message-only windows. Such a window does not receive broadcast messages, has no Z order and is not visible.

    Since you create a message-only window by specifying HWND_MESSAGE as parent parameter in CreateWindowEx you can use FindWindowEx passing HWND_MESSAGE as parent handle for FindWindowEx parameter.

    GetParent should return HWND_MESSAGE
    There are only 10 types of people in the world:
    Those who understand binary and those who do not.

  3. #3
    FindWindowEx does not fit my needs because it assumes that I know the classes of the windows beforehand. Assume that I have no idea what message-only windows there are.


    So,would a function like this work for enumerating message-only windows? If not, I don't see how FindWindowEx is able to search message-only windows quickly.

    Code:
    void DebugOut(const char *fmt, ...){
     va_list a=NULL;
     char szDebugString[1024];
     if(lstrlenA(fmt)==0)return;
     va_start(a,fmt);
     vsprintf(szDebugString,fmt,a);
     va_end(a);
     if(lstrlenA(szDebugString)==0)return;
     OutputDebugString(szDebugString);
     OutputDebugString("\r\n");
    }
    
    BOOL EnumMessageOnlyWindows(WNDENUMPROC wep, LPARAM lParam){
     HWND hwnd;
     DWORD i;
     DebugOut("EnumMessageOnlyWindows start %d",GetTickCount());
     for(i=0;;i+=4){
      hwnd=(HWND)i;
      if(!IsWindow(hwnd))continue;
    #ifdef DEBUGWINDOWS
      DebugOut("%08X %08X %08X",GetWindow(hwnd,GW_HWNDFIRST)
                               ,GetWindow(hwnd,GW_HWNDPREV)
                               ,GetWindow(hwnd,GW_HWNDNEXT));
    #endif
      if(GetParent(hwnd)!=HWND_MESSAGE)
       continue;
    #ifdef DEBUGWINDOWS
      DebugOut("%08X is a message-only window",hwnd);
    #endif
      wep(hwnd,lParam);
      if(i==0xFFFFFFFC)break;
     }
     DebugOut("EnumMessageOnlyWindows end %d",GetTickCount());
     return TRUE;
    }
    Last edited by poccil; September 8th, 2002 at 08:58 AM.

  4. #4
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    In your post you have mentioned that you do not have Windows 2K nor XP.
    What operating system are you using?
    There are only 10 types of people in the world:
    Those who understand binary and those who do not.

  5. #5
    I use Windows 98 Second Edition. I'm writing a window spy program.

  6. #6

  7. #7

  8. #8
    Join Date
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    poccil:

    ...
    You have posted several of "…" and several days I was under impression that somebody else resolved your problem already.

    Just out of curiosity I looked at your thread and found that you were posting yourself triple dots. That does not help to show urgency, it rather shows that you have gotten many answers.

    I could not get back to you any earlier I have to make bread money too. I was away on some errands away from any computer I could use to access code guru.

    Anyway I had a little chance to experiment (you were right documentation is kind of quiet about message only windows). Did you try to do anything?

    Unfortunately I could not find anything else beyond my experience.

    The only way I found is following:

    Code:
    void CTestWnd::EnummerateMessageOnlyWindows()
    {
      HWND hWndFound = ::FindWindowEx(HWND_MESSAGE, NULL, NULL, NULL); //will find first message only window
    
      while(hWndFound)
      {
    
        hWndFound = ::GetNextWindow(hWndFound, GW_HWNDNEXT); 
    
      }
    
    }
    I have confirmed that this is reliable method using Windows 2K, but if newer SDK on your system you will be able to achieve the same results since I am not using 2K specific calls.

    I will try this code on ME at home. Let me know how are you doing.
    There are only 10 types of people in the world:
    Those who understand binary and those who do not.

  9. #9
    Thanks for your function. I never realized that the parameter for the class name can be NULL.

    By the way, I did find a Windows 2000 computer to test, but since it doesn't have any other software on it yet, I cannot use it much for now. During the time I could use it, I discovered that the function I posted does not work.

    I'll definitely try your suggestion in the morning, if I can.

  10. #10
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    FindWindowEx and FindWindow as well can have all formal parameters set to NULL.

    In this case both will find top level window – all windows’ classes and window names will match.
    There are only 10 types of people in the world:
    Those who understand binary and those who do not.

  11. #11
    Thanks, JohnCz, for your help. I've confirmed that the function works successfully. Now my window spy can do what Spy++ failed to do.

  12. #12
    Join Date
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    Location
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    Posts
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    You are welcome.

    How did you get the idea any way? It is interesting idea.
    Besides message only windows is fairly new concept and I think SPY was written before that and never updated.
    There are only 10 types of people in the world:
    Those who understand binary and those who do not.

  13. #13
    I created the Window Viewer both as a way to improve on Spy++ and as a personal programming exercise. Today, In fact, I released a new version if anyone's interested.

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