Q242308: HOWTO: Find a Window Handle from an Instance Handle
Article: Q242308
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:4.0,5.0,6.0
Operating System(s):
Keyword(s): kbAPI kbSDKWin32 kbVBp kbVBp400 kbVBp500 kbVBp600 kbGrpDSVB kbDSupport
Last Modified: 11-JAN-2001
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The information in this article applies to:
- Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0
- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0
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SUMMARY
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The Shell function in Microsoft Visual Basic is used to execute an application.
Often, it is useful to get a Window handle (hWnd) to the application so you can
manipulate it using the Windows APIs. However, the Shell function returns an
Instance handle (hInstance), which is different from a Window handle. This
article shows how to create and use a GetWinHandle() function to return a Window
handle based on an Instance handle.
MORE INFORMATION
================
By using the FindWindow() and GetWindow() APIs (or using EnumWindows in Visual
Basic 5.0 or later), you can loop through the Window handle list. For each
window handle, you can check to see if it has a parent window with GetParent().
If the Window handle does not have a parent handle, you have reached the main
window for an application. You can call GetWindowThreadProcessID(), which yields
the instance handle of the process for the given window handle, to check the
instance handle of the application against the instance handle received from the
Shell() function.
Step-by-Step Example
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1. Start a new Standard EXE project in Visual Basic. Form1 is created by
default.
2. Add a CommandButton (Command1) to the form.
3. From the Project menu, add a new module to the project, and enter the
following declarations and functions:
Public Const GW_HWNDNEXT = 2
Public Declare Function GetParent Lib "user32" (ByVal hwnd As Long) As Long
Public Declare Function GetWindow Lib "user32" (ByVal hwnd As Long, _
ByVal wCmd As Long) As Long
Public Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
(ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Public Declare Function GetWindowText Lib "user32" Alias "GetWindowTextA" _
(ByVal hwnd As Long, ByVal lpString As String, ByVal cch As Long) As Long
Public Declare Function GetWindowThreadProcessId Lib "user32" _
(ByVal hwnd As Long, lpdwprocessid As Long) As Long
Function ProcIDFromWnd(ByVal hwnd As Long) As Long
Dim idProc As Long
' Get PID for this HWnd
GetWindowThreadProcessId hwnd, idProc
' Return PID
ProcIDFromWnd = idProc
End Function
Function GetWinHandle(hInstance As Long) As Long
Dim tempHwnd As Long
' Grab the first window handle that Windows finds:
tempHwnd = FindWindow(vbNullString, vbNullString)
' Loop until you find a match or there are no more window handles:
Do Until tempHwnd = 0
' Check if no parent for this window
If GetParent(tempHwnd) = 0 Then
' Check for PID match
If hInstance = ProcIDFromWnd(tempHwnd) Then
' Return found handle
GetWinHandle = tempHwnd
' Exit search loop
Exit Do
End If
End If
' Get the next window handle
tempHwnd = GetWindow(tempHwnd, GW_HWNDNEXT)
Loop
End Function
4. Add the following code to the form:
Sub Command1_Click()
Dim hInst As Long ' Instance handle from Shell function.
Dim hWndApp As Long ' Window handle from GetWinHandle.
Dim buffer As String ' Holds caption of Window.
Dim numChars As Integer ' Count of bytes returned.
' Shell to an application
hInst = Shell("calc.exe")
' Begin search for handle
hWndApp = GetWinHandle(hInst)
If hWndApp <> 0 Then
' Init buffer
buffer = Space$(128)
' Get caption of window
numChars = GetWindowText(hWndApp, buffer, Len(buffer))
' Display window's caption
MsgBox "You shelled to the Application: " & Left$(buffer, numChars)
End If
End Sub
5. Press the F5 key to run the application. Click Command1 to see that the
Calculator has been shelled and to see a message box displaying "You shelled
to the Application: Calculator."
REFERENCES
==========
Topic in MSDN : "More about handles and process IDs"
For additional information on using the EnumWindows functions to find a specified
window, click the article number below to view the article in the Microsoft
Knowledge Base:
Q183009 HOWTO: Enumerate Windows Using the WIN32 API
For additional information on performing this task in 16-bit versions of VB,
click the article number below to view the article in the Microsoft Knowledge
Base:
Q127030 How to Find a Window Handle Based on an Instance Handle
Additional query words:
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Keywords : kbAPI kbSDKWin32 kbVBp kbVBp400 kbVBp500 kbVBp600 kbGrpDSVB kbDSupport
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600 kbVB400Search kbVB400
Version : WINDOWS:4.0,5.0,6.0
Issue type : kbhowto
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