Howto get the TopMost Form in a WinForm App using Win32 API

public class Win32
{
    public const int GW_HWNDNEXT = 2; // The next window is below the specified window
    public const int GW_HWNDPREV = 3; // The previous window is above
    public const int GW_HWNDFIRST = 0; // TopMost Windows
    private const int SW_HIDE = 0;

    [DllImport("user32", CharSet = CharSet.Auto, SetLastError = true, ExactSpelling = true)]
    public static extern IntPtr GetWindow(IntPtr hwnd, int wFlag);

    [DllImport("user32.dll")]
    static extern IntPtr GetTopWindow(IntPtr hWnd);

    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool IsWindowVisible(IntPtr hWnd);

    [DllImport("user32.dll", CharSet = CharSet.Auto, EntryPoint = "GetWindow",SetLastError = true)]
    public static extern IntPtr GetNextWindow(IntPtr hwnd, [MarshalAs(UnmanagedType.U4)] int wFlag);

    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    static extern int GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount);

    [DllImport("user32.dll")]
    private static extern bool ShowWindowAsync(IntPtr hWnd, int nCmdShow);


    /// <summary>
    /// Cautam Forma care este TopMost si o returnam.
    /// Iteram doar prin ferestrele care sunt vizibile, incepand cu cel mai mare Z-order si continuand
    /// cu cele care se ascund in spatele ei.
    /// </summary>
    /// <returns>Forma care este topmost in momentul apelarii functiei</returns>
    public static Form GetTopMostWindow(IntPtr hWnd_mainFrm)
    {
        Form frm = null;

        IntPtr hwnd = GetTopWindow((IntPtr)null);
        
        //StringBuilder sb = new StringBuilder(256);
        //GetWindowText(hwnd, sb, 256);
        //Console.WriteLine("TOP WINDOW: " + sb.ToString());

        if (hwnd != IntPtr.Zero)
        {
            while ((!IsWindowVisible(hwnd) || frm == null) && hwnd != hWnd_mainFrm)
            {
                // Get next above window if not visible
                hwnd = GetNextWindow(hwnd, GW_HWNDNEXT);
                
                //GetWindowText(hwnd, sb, 256);
                //Console.WriteLine(sb.ToString().Length == 0 ? "Fereastra fara nume" : sb.ToString());

                try
                {
                    frm = (Form)Form.FromHandle(hwnd);
                }
                catch
                {
                    // Crapa daca incercam sa facem cast la un handle care nu e de tip Form
                    // In mod normal daca nu poate face cast returneaza null.
                    // Da la unele cast-uri crapa... pana mea!
                }
            }
        }
        
        return frm;
    }
}