Enumerating Windows/Controls of another application from .Net

Question

I'm developing a small utility application that needs to detect whether another one has one of its MDI child windows open (it's an off-the-shelf Win32 business application over which I have neither source code nor control). From my app, I would like to be able to poll or detect when a particular MDI Child window is open.

In .Net, it's easy to iterate over running processes, but I haven't found an easy way to iterate through the (sub)windows and controls of a given Win32 process from .Net.

Any ideas?

Update
Thanks for the answers they got me on the right path.
I found an article with a test project that uses both EnumWindowsand EnumChidWindows and other API calls to get extended information on controls.

Answer 1

This is an old post, but a common problem. I have a similar situation where I'm trying to control the behaviour of an off-the-shelf software application. I mostly succeeded by using Kixstart, but came up against the limitations of using SETFOCUS and SENDKEYS because at certain points the off-the-shelf software is displaying windows where WindowTitle is blank. So I developed a little utility which identifies visible Windows by their ProcessName as well as WindowTitle (or lack thereof) and sends a message to close a window which matches.

Most of the examples I've seen of EnumWindows callback functions ignore windows which aren't visible or which have blank titles, whereas this code enumerates all windows including invisible ones.

This code is Visual Basic and uses a configuration file in the format

PRC=process name
WIN=window title

Hope this is useful to somebody

Imports System
Imports System.IO
Imports System.Runtime.InteropServices
Imports System.Text
Module Module1
    Dim hShellWindow As IntPtr = GetShellWindow()
    Dim dictWindows As New Dictionary(Of IntPtr, String)
    Dim dictChildWindows As New Dictionary(Of IntPtr, String)
    Dim currentProcessID As Integer = -1
    <DllImport("USER32.DLL")>
    Function GetShellWindow() As IntPtr
    End Function
    <DllImport("USER32.DLL")>
    Function GetForegroundWindow() As IntPtr
    End Function
    <DllImport("USER32.DLL")>
    Function GetWindowText(ByVal hWnd As IntPtr, ByVal lpString As StringBuilder, ByVal nMaxCount As Integer) As Integer
    End Function
    <DllImport("USER32.DLL")>
    Function GetWindowTextLength(ByVal hWnd As IntPtr) As Integer
    End Function
    <DllImport("user32.dll", SetLastError:=True)>
    Function GetWindowThreadProcessId(ByVal hWnd As IntPtr, <Out()> ByRef lpdwProcessId As UInt32) As UInt32
    End Function
    <DllImport("USER32.DLL")>
    Function IsWindowVisible(ByVal hWnd As IntPtr) As Boolean
    End Function
    Delegate Function EnumWindowsProc(ByVal hWnd As IntPtr, ByVal lParam As Integer) As Boolean
    <DllImport("USER32.DLL")>
    Function EnumWindows(ByVal enumFunc As EnumWindowsProc, ByVal lParam As Integer) As Boolean
    End Function
    <DllImport("USER32.DLL")>
    Function EnumChildWindows(ByVal hWndParent As System.IntPtr, ByVal lpEnumFunc As EnumWindowsProc, ByVal lParam As Integer) As Boolean
    End Function
    <DllImport("USER32.DLL")>
    Function PostMessage(ByVal hwnd As Integer, ByVal message As UInteger, ByVal wParam As Integer, ByVal lParam As Integer) As Boolean
    End Function
    <DllImport("USER32.DLL")>
    Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As UInteger, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr
    End Function

    Function enumWindowsInternal(ByVal hWnd As IntPtr, ByVal lParam As Integer) As Boolean
        Dim a As String = ""
        Dim length As Integer = GetWindowTextLength(hWnd)
        If (length > 0) Then
            Dim stringBuilder As New System.Text.StringBuilder(length)
            GetWindowText(hWnd, stringBuilder, (length + 1))
            a = stringBuilder.ToString
        End If
        dictWindows.Add(hWnd, a)
        EnumChildWindows(hWnd, AddressOf enumChildWindowsInternal, 0)
        Return True
    End Function
    Function enumChildWindowsInternal(ByVal hWnd As IntPtr, ByVal lParam As Integer) As Boolean
        Dim a As String = ""
        Dim length As Integer = GetWindowTextLength(hWnd)
        If (length > 0) Then
            Dim stringBuilder As New System.Text.StringBuilder(length)
            GetWindowText(hWnd, stringBuilder, (length + 1))
            a = stringBuilder.ToString
        End If
        dictChildWindows.Add(hWnd, a)
        Return True
    End Function
    Function cleanstring(ByVal a As String) As String
        Dim c As String = ""
        Dim b As String = ""
        Dim i As Integer
        Do While i < Len(a)
            i = i + 1
            c = Mid(a, i, 1)
            If Asc(c) > 31 And Asc(c) < 128 Then
                b = b & c
            End If
        Loop
        cleanstring = b
    End Function
    Sub Main()
        '
        '
        Dim a As String = ""
        Dim b As String = ""
        Dim c As String = ""
        Dim d As String = ""
        Dim f As String = "C:\FIS5\WK.txt"
        Dim a1 As String = ""
        Dim a2 As String = ""
        Dim p As Process
        Dim windows As IDictionary(Of IntPtr, String)
        Dim kvp As KeyValuePair(Of IntPtr, String)
        Dim windowPid As UInt32
        Dim hWnd As IntPtr
        Dim fhWnd As IntPtr
        Dim WM_CLOSE As UInteger = &H12
        Dim WM_SYSCOMMAND As UInteger = &H112
        Dim SC_CLOSE As UInteger = &HF060
        Dim x As Boolean = True
        Dim y As IntPtr
        Dim processes As Process() = Process.GetProcesses
        Dim params As String = File.ReadAllText("C:\FIS5\WindowKiller.txt")
        Dim words As String() = params.Split(vbCrLf)
        Dim word As String
        Dim myprocname As String = ""
        Dim mywinname As String = ""
        Dim i As Integer = 0
        Dim v1 As Integer = 0
        For Each word In words
            word = Trim(cleanstring(word)).ToUpper
            i = InStr(word, "=", CompareMethod.Text)
            ' a = a & word & " " & i.ToString & vbCrLf
            If i = 4 And 4 < Len(word) Then
                If Left(word, 4) = "PRC=" Then
                    myprocname = Mid(word, 5)
                End If
                If Left(word, 4) = "WIN=" Then
                    mywinname = Mid(word, 5)
                End If
            End If
        Next
        a = a & params & vbCrLf & "procname=" & myprocname & ", winname=" & mywinname & vbCrLf
        fhWnd = GetForegroundWindow()
        dictWindows.Clear()
        dictChildWindows.Clear()
        EnumWindows(AddressOf enumWindowsInternal, 0)
        windows = dictChildWindows
        For Each kvp In windows
            hWnd = kvp.Key
            GetWindowThreadProcessId(hWnd, windowPid)
            b = ""
            c = ""
            For Each p In processes
                If p.Id = windowPid Then
                    b = p.ProcessName
                    c = p.Id.ToString
                End If
            Next
            d = "hidden"
            If IsWindowVisible(hWnd) Then
                d = "visible"
            End If
            If hWnd = fhWnd Then
                d = d & ", foreground"
            End If
            a = a & "Child window=" & hWnd.ToString & ", processname=" & b & ", procid=" & c & ", windowname=" & kvp.Value & ", " & d & vbCrLf
        Next
        windows = dictWindows
        For Each kvp In windows
            v1 = 0
            hWnd = kvp.Key
            GetWindowThreadProcessId(hWnd, windowPid)
            b = ""
            c = ""
            For Each p In processes
                If p.Id = windowPid Then
                    b = p.ProcessName
                    c = p.Id.ToString
                End If
            Next
            d = "hidden"
            If IsWindowVisible(hWnd) Then
                d = "visible"
                v1 = 1
            End If
            If hWnd = fhWnd Then
                d = d & ", foreground"
            End If
            word = kvp.Value
            a = a & "Window=" & hWnd.ToString & ", processname=" & b & ", procid=" & c & ", windowname=" & word & ", " & d & vbCrLf
            If Trim(cleanstring(b).ToUpper) = myprocname Then
                a = a & "procname match" & vbCrLf
                If Trim(cleanstring(word)).ToUpper = mywinname And v1 <> 0 Then
                    a = a & "ATTEMPTING To CLOSE: " & b & " # " & word & " # " & c & vbCrLf
                    ' x = PostMessage(hWnd, WM_CLOSE, 0, 0)
                    'If x Then
                    'a = a & "PostMessage returned True" & vbCrLf
                    'Else
                    'a = a & "PostMessage returned False" & vbCrLf
                    'End If
                    y = SendMessage(hWnd, WM_SYSCOMMAND, SC_CLOSE, 0)
                    a = a & "SendMessage returned " & y.ToString & vbCrLf
                End If
            End If
        Next
        My.Computer.FileSystem.WriteAllText(f, a, False)
    End Sub
End Module

Answer 2

You must use native Win32 API.

EnumChildWindows (user32)

[DllImport("user32")]

[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool EnumChildWindows(IntPtr window, EnumWindowProc callback, IntPtr i);

/// <summary>
/// Returns a list of child windows
/// </summary>
/// <param name="parent">Parent of the windows to return</param>
/// <returns>List of child windows</returns>
public static List<IntPtr> GetChildWindows(IntPtr parent)
{
List<IntPtr> result = new List<IntPtr>();
GCHandle listHandle = GCHandle.Alloc(result);
try
{
    EnumWindowProc childProc = new EnumWindowProc(EnumWindow);
    EnumChildWindows(parent, childProc, GCHandle.ToIntPtr(listHandle));
}
finally
{
    if (listHandle.IsAllocated)
    listHandle.Free();
}
return result;
}

/// <summary>
/// Callback method to be used when enumerating windows.
/// </summary>
/// <param name="handle">Handle of the next window</param>
/// <param name="pointer">Pointer to a GCHandle that holds a reference to the list to fill</param>
/// <returns>True to continue the enumeration, false to bail</returns>
private static bool EnumWindow(IntPtr handle, IntPtr pointer)
{
GCHandle gch = GCHandle.FromIntPtr(pointer);
List<IntPtr> list = gch.Target as List<IntPtr>;
if (list == null)
{
    throw new InvalidCastException("GCHandle Target could not be cast as List<IntPtr>");
}
list.Add(handle);
//  You can modify this to check to see if you want to cancel the operation, then return a null here
return true;
}

/// <summary>
/// Delegate for the EnumChildWindows method
/// </summary>
/// <param name="hWnd">Window handle</param>
/// <param name="parameter">Caller-defined variable; we use it for a pointer to our list</param>
/// <returns>True to continue enumerating, false to bail.</returns>
public delegate bool EnumWindowProc(IntPtr hWnd, IntPtr parameter);

Answer 3

You can use P/Invoke to access EnumWindows and EnumChidWindows to itereate through the subwindows/controls of any window.