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Determining hWnd from Process ID....

Posted on 1998-07-17
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Last Modified: 2010-05-03
HI there,

My application uses the Shell command to instigate an instance of a sub-programme.  My question is this - the Shell command returns a double which is the process ID created - is there any way of finding the Window with which the process is associated.  Ideally i'd like to retrieve the hWnd value.

I want to do this so I can post a WM_CLOSE message to the window in order to terminate it gracefully.

Pete
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Question by:peterwest
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alamo earned 400 total points
ID: 1466074
There is no call to get the "window" for a process: there may be none, there may be more than one. Instead you have to use EnumWindows to enumerate all top level windows in the system. In your callback procedure, call GetWindowThreadProcessId to get the ProcessID of the thread which owns the window. When the process IDs match, you've got your window.

I'll post a comment in a moment with some sample code.
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by:alamo
ID: 1466075
Private Declare Function EnumWindows Lib "user32" (ByVal lpEnumFunc As Long, ByVal lParam As Long) As Integer

ProcessID& = Shell("notepad")
ret = EnumWindows(AddressOf EnumWindowsProc, ProcessID&)
If ret = 0 Then MsgBox "failed"

' This must be in a module
Private Declare Function GetWindowThreadProcessId Lib "user32" (ByVal hwnd As Long, lpdwProcessId As Long) As Long

Public Function EnumWindowsProc(ByVal hWind As Long, ByVal lParam As Long) As Boolean
Dim WProcessID&,ThreadID&

 ThreadID& = GetWindowThreadProcessId(hWind, WProcessID&)
 If WProcessID& = lParam Then
  ' send WM_CLOSE here
 End If
 EnumWindowsProc = True  'set to false if you don't want any more enumerated
End Function

That will do it... you will probably get more windows than you expect, but you are at the mercy of EnumWindows as to what windows you get. You might be able to winnow them down with something like:
If IsWindowEnabled(hWind) <> False and If IsWindowVisible(hWind) <> False and If IsIconic(hWind) = False Then

Hope this helps, good luck!
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by:peterwest
ID: 1466076
Hi again,

Sorry for the delay in grading your answer - i've tested the code and it worked fine.

Cheers

Pete
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