Child process window handle

[Keith Waters]

Does anyone know a neat way of getting the handle of the main
window of a child process?

This is the rather messy way I do it now. I launch the child
PB/DLL exe from the parent PB/DLL exe with CreateProcess. The
child process creates its main window and records the handle to
a memory mapped file in a DLL. Meanwhile, the parent process
waits for input idle (WaitForInputIdle) with a time-out of one
second and then calls the same DLL to retrieve the handle. It
works but I'm sure this method cannot be safe.

Thanks, Keith

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[Eric Pearson]

Off the top of my head, you could use EnumWindows to enumerate all of the top level windows. Use GetWindowThreadProcessId to get the process ID that created each window, and when you find one that matches the Process ID that was returned by CreateProcess... Bingo.

Of course whatever you do you will need to wait for the window to be created before you can start scanning for it.

-- Eric


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Perfect Sync Development Tools
Perfect Sync Web Site
Contact Us: mailto:[email protected][email protected]</A>



[This message has been edited by Eric Pearson (edited May 15, 2001).]

[Cecil Williams]

Keith,

If I totally understand what's going on, the GetParent function
retrieves a handle to the specified child window's
parent window. Give that a try!!!!

Cheers,
Cecil

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[Semen Matusovski]

If both apps are own, it's easy to coordinate

Parent.Bas

   #Compile Exe
   #Register None
   #Dim All
   #Include "win32api.inc"

   CallBack Function MainDlgProc
      Select Case CbMsg
         Case %WM_COMMAND
            Dim i As Long, hWndChild As Static Long
            If CbCtl = %IDOK Then i = Shell ("Child.Exe &H" + Hex$(CbHndl, 8))
         Case %WM_USER + 401
            hWndChild = CbWparam: SetWindowText CbHndl, "I am a parent. Child reported hWnd = &H" + Hex$(hWndChild, 8)
       End Select
   End Function

   Function PbMain
      Local hDlg As Long
      Dialog New 0, "Testing", , , 250, 40, %WS_CAPTION Or %WS_SYSMENU To hDlg
      Control Add Button, hDlg, %IDOK, "Start Child.Exe", 10, 10, 230, 15
      Dialog Show Modal hDlg Call MainDlgProc ' Show window
   End Function

Child.Bas

   #Compile Exe
   #Register None
   #Dim All
   #Include "win32api.inc"

   CallBack Function DlgProc
      Select Case CbMsg
         Case %WM_INITDIALOG
           PostMessage CbHndl, %WM_USER + 501, 0, 0
        Case %WM_USER + 501   
           SendMessage Val(Command$), %WM_USER + 401, CbHndl, 0
           SetForegroundWindow Val(Command$)
      End Select
   End Function

   Function PbMain
      Local hDlg As Long
      Dialog New 0, "", 0, 0, 200, 80, %WS_CAPTION Or %WS_SYSMENU To hDlg
      SetWindowText hDlg, "I am a child (hwnd = &H" + Hex$(hDlg, 8) + ")"
      Dialog Show Modal hDlg Call DlgProc ' Show window
   End Function

If second app is not own, it's possible to use a hook (somehow I posted a sample)

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E-MAIL: [email protected]

[Keith Waters]

Eric

Your scheme makes sense to me and I'm trying it. Cannot quite get
it to work properly yet as I seem to picking up wrong window handle.
I will try again tomorrow. Many thanks.

Semen

Your replies are always very interesting. I'm already using the
same interprocess communication as you suggest for other purposes
and so maybe I will use your method if I fail to get Eric's
aproach working. Again, many thanks.

Keith

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[Semen Matusovski]

EnumWindows is not a problem

   #Compile Exe
   #Dim All
   #Register None
   #Include "Win32Api.Inc"

   Global hNotepad As Long, hDlg As Long
   
   Function EnumWindowsCallBack(ByVal hwnd As Long, ByVal lParam As Long) As Long
       Local kProc As Long
       GetWindowThreadProcessId hWnd, kproc
       If kProc = lParam Then hNotePad = hWnd
       Function = 1
    End Function

   CallBack Function StartNotepad
      Dim eProc As Long
      Dim proc As PROCESS_INFORMATION
      Dim start As STARTUPINFO
      start.cb = SizeOf(start)
      If CreateProcess (ByVal 0&, "Notepad.exe", ByVal 0&, ByVal 0&, 1&, _
         %NORMAL_PRIORITY_CLASS, ByVal 0&, ByVal 0&, start, proc) Then eProc = proc.dwProcessId: _
         CloseHandle proc.hThread: CloseHandle proc.hProcess Else Exit Function
         
      While hNotepad = 0
         Sleep 50
         EnumWindows CodePtr(EnumWindowsCallBack), eProc
      Wend
      
      ShowWindow CbHndl, 0
      MessageBox CbHndl, "Click Ok to close Notepad's window", "Semen", %MB_TASKMODAL
      ShowWindow CbHndl, 1
      SendMessage hNotePad, %WM_SYSCOMMAND, %SC_CLOSE, 0
      hNotePad = 0
      
   End Function

   Function PbMain
      Dialog New hDlg, "test", , , 70, 30, %WS_SYSMENU Or %WS_CAPTION, %WS_EX_TOPMOST To hdlg
      Control Add Button, hDlg, %IDOK, "Start Notepad", 10, 10, 50, 15 Call StartNotePad
      Dialog Show Modal hDlg
   End Function

CBT- hook ... I found, but it was global (because I integrated own DLL).
So, here it's not comfortable way.

[This message has been edited by Semen Matusovski (edited May 15, 2001).]

[Keith Waters]

Semen

I think I'm doing the same, as follows.

GLOBAL g_tempDword AS DWORD

FUNCTION CheckForProcess (BYVAL hWnd AS LONG, BYVAL procID AS LONG) AS LONG
  LOCAL wProcID AS LONG

  CALL GetWindowThreadProcessId (hWnd, wProcID)

  IF wProcID = procID THEN
    g_tempDword = hWnd
    FUNCTION = %FALSE         'Stop enumerating
  ELSE
    FUNCTION = %TRUE
  END IF
END FUNCTION

FUNCTION ProcessMainWindow (BYVAL procId AS LONG) AS LONG

  g_tempDword = %NULL
  CALL EnumWindows (CODEPTR(CheckForProcess), procId)
  FUNCTION = g_tempDword
END FUNCTION

First I call CreateProcess to launch the process and then I do

  CALL WaitForInputIdle (pi.hProcess, 1000)  'We wait for upto 1 s

  g_hWndInspector = ProcessMainWindow (pi.dwProcessId)

Can't see why its not working. I think its getting a window of the
child exe but not the main window.

Keith

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[Semen Matusovski]

Keith --
Do you use WaitForInputIdle after or before CloseHandle pi.hProcess ?
If after, I guess that WaitForInputIdle returns "failed" (-1).
At least, this so under Win2000.

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E-MAIL: [email protected]

[Keith Waters]

Semen

I use WaitForInputIdle before CloseHandle as follows.

  CALL WaitForInputIdle (pi.hProcess, 1000)  'We wait for upto 1 s
  
  'Get inspector main window handle  
' g_hWndInspector = GetProcHWin()                      'Old method 
  g_hWndInspector = ProcessMainWindow (pi.dwProcessId) 'New method

  'Close process and thread handles (unless we need them)
  CALL CloseHandle (pi.hProcess)
  CALL CloseHandle (pi.hThread)

The old method (commented out) worked fine. The new method returns
a window handle but its not the main process window. When I get back
to my development machine I will find out what window it is picking up.
In the meantime, many thanks to you and Eric.

Keith

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[Keith Waters]

Here is an update to enumerating process windows (for anyone still interested).

I've checked and the EnumWindows function is passing parent and child window
handles back to the callback function. But hang on, the MSDN documentation
says that EnumWindows does not enumerate child windows. My process creates
a total of 6 windows before settling into input idle, a main window and 5
child windows, and I'm seeing all 6 in the callback.

So, I've double checked to make sure I'm including the %WS_CHILD style for
all except the main window and that I'm specifying a valid parent handle
(handle of main window, of course). It seems correct.

In my callback function I return %FALSE to end enumeration when I get the
first window belonging to the process. If instead I return %TRUE so that
enumeration continues, I get the last window belonging to the process.
In neither case is it the main window and I wouldn't expect it to be
because EnumWindows does not guarantee to enumerate in any particular order,
which is fair enough.

I will try calling GetParent(hWnd) in my callback function and checking if
the return value is %NULL. If it is then presumable that must be the main
window (ie. the only one without a parent). But I'm still puzzled why
EnumWindows is enumerating parent and children.

Keith

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[This message has been edited by Keith Waters (edited May 17, 2001).]

[Lance Edmonds]

EnumWindows enumerates top-level windows... there may be more than one top-level window per app or process.

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Keith Waters]

Yes Lance, I agree and the documentation emphasises by saying, quote
"The EnumWindows function does not enumerate child windows.".
My app only creates one top-level, all other windows are children.
Is the documentation wrong here?

Keith

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[This message has been edited by Keith Waters (edited May 17, 2001).]

[Semen Matusovski]

Meanwhile EnumWindows enumerates some child system windows (under Windows2000 - classname ComboLBox).

One thought - wrong combinations of styles (for example, %WS_CHILD together with %WS_POPUP)

   #Compile Exe
   #Dim All
   #Register None
   #Include "Win32Api.Inc"
   
   Function EnumWindowsCallBack(ByVal hwnd As Long, ByVal lParam As Long) As Long
       Local kProc As Long
       GetWindowThreadProcessId hWnd, kproc
       If kProc = GetCurrentProcessId Then _
          If (GetWindowLong(hWnd, %GWL_STYLE) And %WS_CHILD) = %WS_CHILD Then MsgBox "Child " + Hex$(hWnd)
       Function = 1
    End Function
   CallBack Function DlgProc
      Dim i As Long, hdlg(5) As Long
      Select Case CbMsg
         Case %WM_INITDIALOG
            For i = 1 To 5
               Dialog New CbHndl, "test" + Str$(i), 30 * i, 30 * i, 70, 100, %WS_CHILD Or %WS_POPUP Or %WS_BORDER To hdlg(i)
               Dialog Show Modeless hDlg(i)
            Next
      End Select
   End Function
   CallBack Function StartNotepad
      EnumWindows CodePtr(EnumWindowsCallBack), 0
      Dialog End CbHndl
   End Function
   Function PbMain
      Dim hDlg As Long
      Dialog New 0, "test", , , 400, 300, %WS_POPUP To hdlg
      Control Add Button, hDlg, %IDOK, "Start Notepad", 200, 100, 50, 15 Call StartNotePad
      Dialog Show Modal hDlg Call DlgProc
   End Function

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E-MAIL: [email protected]

[Keith Waters]

Semen

I've just checked for %WS_POPUP combined with %WS_CHILD and found
none. I'll check for other wrong combinations but I would have
thought if ther were any I'd have noticed other strange effects.
Thanks for alerting me to that possibility, tho.

Also, I'd thought of checking the window style GetWindowLong as
you suggest and I also thought of using GetParent. But the
central issue is why should all this be necessary when EnumWindows
is supposed to enumerate only top-level windows (ie. those with
no parent except the desktop). I feel I must be doing something
wrong but cannot trace it.

Thank anyway, Keith

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[Keith Waters]

The update.

The following worked.

GLOBAL g_tempDword AS DWORD
  
FUNCTION CheckForProcess (BYVAL hWnd AS LONG, BYVAL procID AS LONG) AS LONG
  LOCAL wProcID AS LONG
 
  CALL GetWindowThreadProcessId (hWnd, wProcID)
 
  IF wProcID = procID THEN           'If window of process
    IF %NULL = GetParent(hWnd) THEN  'If has no parent
      g_tempDword = hWnd             'Note window handle
      FUNCTION = %FALSE              'Stop enumerating
      EXIT FUNCTION
    END IF
  END IF
  FUNCTION = %TRUE                   'Continue enumerating
END FUNCTION
 
FUNCTION ProcessMainWindow (BYVAL procId AS LONG) AS LONG
  g_tempDword = %NULL
  CALL EnumWindows (CODEPTR(CheckForProcess), procId)
  FUNCTION = g_tempDword
END FUNCTION

The following didn't work because more than one window in the enumeration
passed the "(GetWindowLong (hWnd, %GWL_STYLE) AND %WS_CHILD) = 0" test
(sounds like Lance's point).

GLOBAL g_tempDword AS DWORD
 
FUNCTION CheckForProcess (BYVAL hWnd AS LONG, BYVAL procID AS LONG) AS LONG
  LOCAL wProcID AS LONG
 
  CALL GetWindowThreadProcessId (hWnd, wProcID)
 
  IF wProcID = procID THEN
    IF (GetWindowLong (hWnd, %GWL_STYLE) AND %WS_CHILD) = 0 THEN
      g_tempDword = hWnd        'Note window handle
      FUNCTION = %FALSE         'Stop enumerating
      EXIT FUNCTION
    END IF
  END IF
  FUNCTION = %TRUE            'Continue enumerating
END FUNCTION
 
FUNCTION ProcessMainWindow (BYVAL procId AS LONG) AS LONG
  g_tempDword = %NULL
  CALL EnumWindows (CODEPTR(CheckForProcess), procId)
  FUNCTION = g_tempDword
END FUNCTION

Keith

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