using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Runtime.InteropServices;

namespace WpfSendMsg
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        const int WM_COPYDATA = 0x004A;
        [DllImport("User32.dll", EntryPoint = "SendMessage")]
        private static extern int SendMessage(
            int hWnd, // handle to destination BR>            
            int Msg, // message
            int wParam, // first message parameter
            ref COPYDATASTRUCT lParam // second message parameter
        );

        [DllImport("User32.dll", EntryPoint = "FindWindow")]
        private static extern int Find(string lpClassName, string lpame);

        public Window1()
        {
            InitializeComponent();
            this.Title = "SentWindow";
        }

        private void btn1_Click(object sender, RoutedEventArgs e)
        {
            //int HANDLER = Findnull, @"欲发送程序窗口的标题");
            int HANDLER = Find(null, @"WindowGet");
            if (HANDLER != 0)
            {
                byte[] sarr = System.Text.Encoding.Default.GetBytes(tb1.Text);
                int len = sarr.Length;
                COPYDATASTRUCT cds;
                cds.dwData = (IntPtr)100;
                cds.lpData = tb1.Text;
                cds.cbData = len + 1;
                SendMessage(HANDLER, WM_COPYDATA, 0, ref cds);
            }
        }
    }

    public struct COPYDATASTRUCT
    {
        public IntPtr dwData;
        public int cbData;
        [MarshalAs(UnmanagedType.LPStr)]
        public string lpData;
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Runtime.InteropServices;
using System.Windows.Interop;

namespace GetMsg
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        const int WM_COPYDATA = 0x004A;

        public Window1()
        {
            InitializeComponent();
            this.Title = "WindowGet";
            SourceInitialized += AppWindow_SourceInitialized;
        }

        private void AppWindow_SourceInitialized(object sender, EventArgs e)
        {
            WindowInteropHelper helper = new WindowInteropHelper(this);

            HwndSource hwndSource = HwndSource.FromHwnd(helper.Handle);
            hwndSource.AddHook(new HwndSourceHook(WndProc));
            
        }


        IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
        {
            int retVal = 0;
            handled = false;

            switch ((int)msg)
            {
                case WM_COPYDATA:
                    {
                        
                        try
                        {
                            COPYDATASTRUCT cp = (COPYDATASTRUCT)Marshal.PtrToStructure(lParam, typeof(COPYDATASTRUCT));
                            
                            tb1.Text = cp.lpData;
                        }
                        catch (Exception e)
                        {
                            System.Diagnostics.Debug.WriteLine(e.ToString());
                        }
                        handled = true;
                        retVal = 1;

                        break;
                    }
                default:
                    break;
            }

            return (IntPtr)retVal;
        }

        public struct COPYDATASTRUCT
        {
            public IntPtr dwData;
            public int cbData;
            [MarshalAs(UnmanagedType.LPStr)]
            public string lpData;
        }


    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Runtime.InteropServices;

namespace WpfSendMsg
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        const int WM_COPYDATA = 0x004A;
        [DllImport("User32.dll", EntryPoint = "SendMessage")]
        private static extern int SendMessage(
            int hWnd, // handle to destination BR>            
            int Msg, // message
            int wParam, // first message parameter
            ref COPYDATASTRUCT lParam // second message parameter
        );

        [DllImport("User32.dll", EntryPoint = "FindWindow")]
        private static extern int Find(string lpClassName, string lpame);

        public Window1()
        {
            InitializeComponent();
            this.Title = "SentWindow";
        }

        private void btn1_Click(object sender, RoutedEventArgs e)
        {
            //int HANDLER = Findnull, @"欲发送程序窗口的标题");
            int HANDLER = Find(null, @"WindowGet");
            if (HANDLER != 0)
            {
                byte[] sarr = System.Text.Encoding.Default.GetBytes(tb1.Text);
                int len = sarr.Length;
                COPYDATASTRUCT cds;
                cds.dwData = (IntPtr)100;
                cds.lpData = tb1.Text;
                cds.cbData = len + 1;
                SendMessage(HANDLER, WM_COPYDATA, 0, ref cds);
            }
        }
    }

    public struct COPYDATASTRUCT
    {
        public IntPtr dwData;
        public int cbData;
        [MarshalAs(UnmanagedType.LPStr)]
        public string lpData;
    }
}