HOWTO: Enumerate Windows Using the WIN32 API

ID: Q183009

The information in this article applies to:

Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 6.0
Microsoft Visual Basic Control Creation, Learning, Professional, and Enterprise Editions for Windows, version 5.0

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

Start a new project in Visual Basic. Form1 is created by default.

Add two CommandButtons and a TextBox.

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

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

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.)

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.

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

Additional query words: find locate Callback

Keywords : kbAPI kbSDKWin32 kbVBp kbVBp500 kbVBp600 kbGrpVB kbDSupport
Version : WINDOWS:5.0,6.0
Platform : WINDOWS
Issue type : kbhowto