About message-only windows

[poccil]

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.

[JohnCz]

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

[poccil]

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.

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;
}

[JohnCz]

In your post you have mentioned that you do not have Windows 2K nor XP.
What operating system are you using?

[poccil]

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

[poccil]

...

[poccil]

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[JohnCz]

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:

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.

[poccil]

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.

[JohnCz]

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.

[poccil]

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

[JohnCz]

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.

[poccil]

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.