using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

using System.Runtime.InteropServices;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            System.Diagnostics.Debug.Print(System.Diagnostics.Process.GetCurrentProcess().MainWindowHandle.ToString("X8"));
            System.Diagnostics.Debug.Print(CFindWindow.FindMainWindowFromProcessId(System.Diagnostics.Process.GetCurrentProcess().Id).ToString("X8"));
            System.Diagnostics.Debug.Print(CFindWindow.FindMainWindowFromCurrentProcessId().ToString("X8"));
            System.Diagnostics.Debug.Print(CFindWindow.FindWindow(null, "Form1").ToString("X8"));
            System.Diagnostics.Debug.Print(CFindWindow.FindWindowEx(IntPtr.Zero, IntPtr.Zero, null, "Form1").ToString("X8"));
        }
    }
    public static class CFindWindow
    {
        private delegate bool EnumWindowsProc(IntPtr hWnd,IntPtr lParam);
        [DllImport("user32.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Winapi)]
        private extern static bool EnumWindows(EnumWindowsProc EnumProc,IntPtr lParam);
        [DllImport("user32.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Winapi)]
        private extern static IntPtr GetAncestor(IntPtr hWnd, int gaFlags);
        [DllImport("user32.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Winapi)]
        private extern static int GetWindowThreadProcessId(IntPtr hWnd, ref int lpdwProcessId);
        [DllImport("user32.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Winapi)]
        public extern static IntPtr FindWindow(string lpszClass, string lpszWindow);
        [DllImport("user32.dll", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Winapi)]
        public extern static IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter,string lpszClass, string lpszWindow);

        // GetAncestor Flags
        private const int GA_PARENT = 1;
        private const int GA_ROOT = 2;
        private const int GA_ROOTOWNER = 3;

        private static IntPtr m_Wnd;

        private static bool _EnumWindowsProc(IntPtr hWnd, IntPtr lParam)
        {
            int dwProcessId = 0;
            GetWindowThreadProcessId(hWnd,ref dwProcessId);
            if (dwProcessId == (int)lParam)
            {
                m_Wnd = GetAncestor(hWnd, GA_ROOTOWNER);
                return false;
            }
            return true;
        }

        public static IntPtr FindMainWindowFromProcessId(int nProcess)
        {
            m_Wnd = IntPtr.Zero;
            EnumWindows(_EnumWindowsProc, (IntPtr)nProcess);
            return m_Wnd;
        }

        public static IntPtr FindMainWindowFromCurrentProcessId()
        {
            return FindMainWindowFromProcessId(System.Diagnostics.Process.GetCurrentProcess().Id);
        }
    }
}