C# Signature:

[DllImport("user32.dll")]
static extern bool EnumDesktopWindows(IntPtr hDesktop,
   EnumDesktopWindowsDelegate lpfn, IntPtr lParam);

VB.net Signature:

Private Declare Auto Function EnumDesktopWindows Lib "user32" (ByVal hDesktop As IntPtr, ByVal lpEnumCallbackFuntion As enumdelegate, ByVal lParam As IntPtr) As Boolean

User-Defined Types:

None.

Notes:

None.

Tips & Tricks:

Please add some!

Sample Code:

using System;
using System.Text;
using System.Collections;
using System.Runtime.InteropServices;

/// <summary>
/// EnumDesktopWindows Demo - shows the caption of all desktop windows.
/// Authors: Svetlin Nakov, Martin Kulov
/// Bulgarian Association of Software Developers - http://www.devbg.org/en/
/// </summary>

public class EnumDesktopWindowsDemo
{
    const int MAXTITLE = 255;

    private static ArrayList mTitlesList;

    private delegate bool EnumDelegate(IntPtr hWnd, int lParam);

    [DllImport("user32.dll",
        EntryPoint="EnumDesktopWindows",
        ExactSpelling = false,
        CharSet=CharSet.Auto,
        SetLastError=true)]
    private static extern bool _EnumDesktopWindows(IntPtr hDesktop,
        EnumDelegate lpEnumCallbackFunction,
        IntPtr lParam);

    [DllImport("user32.dll",
        EntryPoint="GetWindowText",
        ExactSpelling=false,
        CharSet=CharSet.Auto,
        SetLastError=true)]
    private static extern int _GetWindowText(IntPtr hWnd,
        StringBuilder lpWindowText,
        int nMaxCount);

    private static bool EnumWindowsProc(IntPtr hWnd, int lParam)
    {
        string title = GetWindowText(hWnd);
        mTitlesList.Add(title);

        return true;
    }

    /// <summary>
    /// Returns the caption of a windows by given HWND identifier.
    /// </summary>
    public static string GetWindowText(IntPtr hWnd)
    {
        StringBuilder title = new StringBuilder(MAXTITLE);
        int titleLength = _GetWindowText(hWnd, title, title.Capacity + 1);
        title.Length = titleLength;

        return title.ToString();
    }

    /// <summary>
    /// Returns the caption of all desktop windows.
    /// </summary>
    public static string[] GetDesktopWindowsCaptions()
    {
        mTitlesList = new ArrayList();
        EnumDelegate enumfunc = new EnumDelegate(EnumWindowsProc);
        IntPtr hDesktop = IntPtr.Zero; // current desktop
        bool success = _EnumDesktopWindows(hDesktop, enumfunc, IntPtr.Zero);

        if (success)
        {
            // Copy the result to string array

            string[] titles = new string[mTitlesList.Count];
            mTitlesList.CopyTo(titles);
            return titles;
        }
        else
        {
            // Get the last Win32 error code
            int errorCode = Marshal.GetLastWin32Error();

            string errorMessage = String.Format("EnumDesktopWindows failed with code {0}.", errorCode);
            throw new Exception(errorMessage);
        }
    }

    static void Main()
    {
        string[] desktopWindowsCaptions = GetDesktopWindowsCaptions();

        foreach (string caption in desktopWindowsCaptions)
            Console.WriteLine(caption);
    }
}

Sample Code (VB.net):

    Const MAXTITLE As Integer = 255
    Public Shared mTitlesList As ArrayList
    Public Delegate Function EnumDelegate(ByVal hWnd As IntPtr, ByVal lParam As Integer) As Boolean

    Private Shared Function EnumWindowsProc(ByVal hWnd As IntPtr, ByVal lParam As Integer) As Boolean
    Dim title As String = GetWindowText(hWnd)
    mTitlesList.Add(title)
    Return True
    End Function

    Public Shared Function GetWindowText(ByVal hWnd As IntPtr) As String
    Dim title As System.Text.StringBuilder = New System.Text.StringBuilder(MAXTITLE)
    Dim titleLength As Integer = GetWindowText(hWnd, title, (title.Capacity + 1))
    title.Length = titleLength
    Return title.ToString
    End Function

    Public Shared Function GetDesktopWindowsCaptions() As String()
    mTitlesList = New ArrayList
    Dim enumfunc As EnumDelegate = New EnumDelegate(AddressOf EnumWindowsProc)
    Dim hDesktop As IntPtr = IntPtr.Zero
    ' current desktop
    Dim success As Boolean = EnumDesktopWindows(hDesktop, enumfunc, IntPtr.Zero)
    If success Then
        ' Copy the result to string array
        Dim titles() As String = New String((mTitlesList.Count) - 1) {}
        mTitlesList.CopyTo(titles)
        Return titles
    Else
        ' Get the last Win32 error code
        Dim errorMessage As String = String.Format("EnumDesktopWindows failed.")
        Throw New Exception(errorMessage)
    End If
    End Function

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Dim desktopWindowsCaptions() As String = GetDesktopWindowsCaptions()
    For Each caption As String In desktopWindowsCaptions
        Console.WriteLine(caption)
    Next
    End Sub

Alternative Managed API:

Do you know one? Please contribute it!