How To Enumerate Windows Using the WIN32 API

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Article ID: 183009 - View products that this article applies to.
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SUMMARY

You can list Windows, including Child Windows, using the GetWindow API. However, an application that calls GetWindow to perform this task risks being caught in an infinite loop or referencing a handle to a window that has been destroyed. Using EnumWindows for top-level Windows and EnumChildWindows for Child Windows or EnumThreadWindows for all non-child windows associated with a thread is a preferred method and is demonstrated in this article.

MORE INFORMATION

EnumWindows enumerates all top-level Windows, but not Child Windows. The EnumChildWindows function does not enumerate top-level windows owned by the specified window nor does it enumerate any other owned windows. The EnumThreadWindows function enumerates all non-child windows associated with a thread. This sample uses all three to list the Class and Title of Windows it finds. Note that while all Windows have a Class, not all have a Title.

Step-by-Step Example

  1. Start a new project in Visual Basic. Form1 is created by default.
  2. Add two CommandButtons and a TextBox.
  3. Copy the following code into the Form's module:
          Option Explicit
    
          Private Sub Command1_Click()
             Dim lRet As Long, lParam As Long
             Dim lhWnd As Long
    
             lhWnd = Me.hwnd  ' Find the Form's Child Windows
             ' Comment the line above and uncomment the line below to
             ' enumerate Windows for the DeskTop rather than for the Form
             'lhWnd = GetDesktopWindow()  ' Find the Desktop's Child Windows
             ' enumerate the list
             lRet = EnumChildWindows(lhWnd, AddressOf EnumChildProc, lParam)
          End Sub
    
          Private Sub Command2_Click()
             Dim lRet As Long
             Dim lParam As Long
    
             'enumerate the list
             lRet = EnumWindows(AddressOf EnumWinProc, lParam)
             ' How many Windows did we find?
             Debug.Print TopCount; " Total Top level Windows"
             Debug.Print ChildCount; " Total Child Windows"
             Debug.Print ThreadCount; " Total Thread Windows"
             Debug.Print "For a grand total of "; TopCount + _
             ChildCount + ThreadCount; " Windows!"
          End Sub
    					
  4. Add a Module with the following code:
          Option Explicit
    
          Type RECT
             Left As Long
             Top As Long
             Right As Long
             Bottom As Long
          End Type
    
          Declare Function GetWindowRect Lib "user32" (ByVal hwnd As Long, _
             lpRect As RECT) As Long
    
          Declare Function MoveWindow Lib "user32" (ByVal hwnd As Long, _
             ByVal x As Long, ByVal y As Long, ByVal nWidth As Long, _
             ByVal nHeight As Long, ByVal bRepaint As Long) As Long
    
          Declare Function GetDesktopWindow Lib "user32" () As Long
    
          Declare Function EnumWindows Lib "user32" _
             (ByVal lpEnumFunc As Long, ByVal lParam As Long) As Long
    
          Declare Function EnumChildWindows Lib "user32" (ByVal hWndParent _
             As Long, ByVal lpEnumFunc As Long, ByVal lParam As Long) As Long
    
          Declare Function EnumThreadWindows Lib "user32" (ByVal dwThreadId _
             As Long, ByVal lpfn As Long, ByVal lParam As Long) As Long
    
          Declare Function GetWindowThreadProcessId Lib "user32" _
             (ByVal hwnd As Long, lpdwProcessId As Long) As Long
    
          Declare Function GetClassName Lib "user32" Alias "GetClassNameA" _
             (ByVal hwnd As Long, ByVal lpClassName As String, _
             ByVal nMaxCount As Long) As Long
    
          Declare Function GetWindowText Lib "user32" Alias "GetWindowTextA" _
             (ByVal hwnd As Long, ByVal lpString As String, _
             ByVal cch As Long) As Long
    
          Public TopCount As Integer     ' Number of Top level Windows
          Public ChildCount As Integer   ' Number of Child Windows
          Public ThreadCount As Integer  ' Number of Thread Windows
    
          Function EnumWinProc(ByVal lhWnd As Long, ByVal lParam As Long) _
             As Long
             Dim RetVal As Long, ProcessID As Long, ThreadID As Long
             Dim WinClassBuf As String * 255, WinTitleBuf As String * 255
             Dim WinClass As String, WinTitle As String
    
             RetVal = GetClassName(lhWnd, WinClassBuf, 255)
             WinClass = StripNulls(WinClassBuf)  ' remove extra Nulls & spaces
             RetVal = GetWindowText(lhWnd, WinTitleBuf, 255)
             WinTitle = StripNulls(WinTitleBuf)
             TopCount = TopCount + 1
             ' see the Windows Class and Title for each top level Window
             Debug.Print "Top level Class = "; WinClass; ", Title = "; WinTitle
             ' Usually either enumerate Child or Thread Windows, not both.
             ' In this example, EnumThreadWindows may produce a very long list!
             RetVal = EnumChildWindows(lhWnd, AddressOf EnumChildProc, lParam)
             ThreadID = GetWindowThreadProcessId(lhWnd, ProcessID)
             RetVal = EnumThreadWindows(ThreadID, AddressOf EnumThreadProc, _
             lParam)
             EnumWinProc = True
          End Function
    
          Function EnumChildProc(ByVal lhWnd As Long, ByVal lParam As Long) _
             As Long
             Dim RetVal As Long
             Dim WinClassBuf As String * 255, WinTitleBuf As String * 255
             Dim WinClass As String, WinTitle As String
             Dim WinRect As RECT
             Dim WinWidth As Long, WinHeight As Long
    
             RetVal = GetClassName(lhWnd, WinClassBuf, 255)
             WinClass = StripNulls(WinClassBuf)  ' remove extra Nulls & spaces
             RetVal = GetWindowText(lhWnd, WinTitleBuf, 255)
             WinTitle = StripNulls(WinTitleBuf)
             ChildCount = ChildCount + 1
             ' see the Windows Class and Title for each Child Window enumerated
             Debug.Print "   Child Class = "; WinClass; ", Title = "; WinTitle
             ' You can find any type of Window by searching for its WinClass
             If WinClass = "ThunderTextBox" Then    ' TextBox Window
                RetVal = GetWindowRect(lhWnd, WinRect)  ' get current size
                WinWidth = WinRect.Right - WinRect.Left ' keep current width
                WinHeight = (WinRect.Bottom - WinRect.Top) * 2 ' double height
                RetVal = MoveWindow(lhWnd, 0, 0, WinWidth, WinHeight, True)
                EnumChildProc = False
             Else
                EnumChildProc = True
             End If
          End Function
    
          Function EnumThreadProc(ByVal lhWnd As Long, ByVal lParam As Long) _
             As Long
             Dim RetVal As Long
             Dim WinClassBuf As String * 255, WinTitleBuf As String * 255
             Dim WinClass As String, WinTitle As String
    
             RetVal = GetClassName(lhWnd, WinClassBuf, 255)
             WinClass = StripNulls(WinClassBuf)  ' remove extra Nulls & spaces
             RetVal = GetWindowText(lhWnd, WinTitleBuf, 255)
             WinTitle = StripNulls(WinTitleBuf)
             ThreadCount = ThreadCount + 1
             ' see the Windows Class and Title for top level Window
             Debug.Print "Thread Window Class = "; WinClass; ", Title = "; _
             WinTitle
             EnumThreadProc = True
          End Function
    
          Public Function StripNulls(OriginalStr As String) As String
             ' This removes the extra Nulls so String comparisons will work
             If (InStr(OriginalStr, Chr(0)) > 0) Then
                OriginalStr = Left(OriginalStr, InStr(OriginalStr, Chr(0)) - 1)
             End If
             StripNulls = OriginalStr
          End Function
    
    					
  5. Run the project and click on Command1. This enumerates the Form's child Windows until it finds the TextBox, then doubles the height of the TextBox and moves it to position 0, 0 (upper-left of the Form.)
  6. Click on Command2. It now lists the Class and Title (if there is one) for all top-level Windows, for their Child Windows, and any non-child Windows associated with their threads, to the Immediate Window. Note that this can be a very long list and may take a minute to complete.
  7. From the Run Menu, choose End, or click the END button to stop the program. Change the code in Sub Command1_Click according to the comments to pass the handle from GetDesktopWindow. Run the project and click on Command1 to enumerate all child Windows of the DeskTop. Note that this procedure can take some time to complete.

REFERENCES

For more information, please search on the following topics in either the Win32 Programmer's Reference or the Microsoft Developer Network (MSDN) Library CD-ROM:

  • EnumWindows
  • EnumChildWindows
  • EnumThreadWindows
  • GetDesktopWindow
  • GetClassName
  • GetWindowRect
  • GetWindowText
  • GetWindowThreadProcessId
  • MoveWindow

Properties

Article ID: 183009 - Last Review: July 1, 2004 - Revision: 2.1
APPLIES TO
  • Microsoft Visual Basic 6.0 Learning Edition
  • Microsoft Visual Basic 6.0 Professional Edition
  • Microsoft Visual Basic 6.0 Enterprise Edition
  • Microsoft Visual Basic 5.0 Control Creation Edition
  • Microsoft Visual Basic 5.0 Learning Edition
  • Microsoft Visual Basic 5.0 Professional Edition
  • Microsoft Visual Basic 5.0 Enterprise Edition
Keywords: 
kbhowto kbapi KB183009

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