C# Interprocess Communication

Send a WM_COPYDATA message to another process using SendMessage

Send side:

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 SentTest
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            this.Title = "发送窗口";
        }

        const int WM_COPYDATA = 0x004A;

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

        [DllImport("User32.dll")]
        public static extern int SendMessage(int hwnd, int msg, int wParam, ref COPYDATASTRUCT IParam);
        [DllImport("User32.dll")]
        public static extern int FindWindow(string lpClassName, string lpWindowName);

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            String strSent = "需要发送的信息";

            int WINDOW_HANDLE = FindWindow(null, "接收窗口");
            if (WINDOW_HANDLE != 0)
            {
                byte[] arr = System.Text.Encoding.Default.GetBytes(strSent);
                int len = arr.Length;
                COPYDATASTRUCT cdata;
                cdata.dwData = (IntPtr)100;
                cdata.lpData = strSent;
                cdata.cData = len + 1;
                SendMessage(WINDOW_HANDLE, WM_COPYDATA, 0, ref cdata);
            }
        }
    }
}

Get side:

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 GetTest
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        IntPtr hwnd;
        public MainWindow()
        {
            InitializeComponent();
            this.Title = "接受窗口";

            this.Loaded += new RoutedEventHandler(MainWindow_Loaded);
            this.Closed += new EventHandler(MainWindow_Closed);
        }

        void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            //窗口加载完毕才可用，否则会报错。
            hwnd = new WindowInteropHelper(this).Handle;
            HwndSource source = HwndSource.FromHwnd(hwnd);
            if (source != null) source.AddHook(WndProc);
        }

        void MainWindow_Closed(object sender, EventArgs e)
        {
            try
            {
                HwndSource.FromHwnd(hwnd).RemoveHook(WndProc);
            }
            catch (Exception)
            {

                throw;
            }

        }

        const int WM_COPYDATA = 0x004A;//WM_COPYDATA消息的主要目的是允许在进程间传递只读数据。
        //Windows在通过WM_COPYDATA消息传递期间，不提供继承同步方式。
        //其中,WM_COPYDATA对应的十六进制数为0x004A
        public struct COPYDATASTRUCT
        {
            public IntPtr dwData;
            public int cData;
            [MarshalAs(UnmanagedType.LPStr)]
            public string lpData;
        }

        //wpf用此方法
        private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
        {
            if (msg == WM_COPYDATA)
            {
                COPYDATASTRUCT cdata = new COPYDATASTRUCT();
                Type mytype = cdata.GetType();
                cdata = (COPYDATASTRUCT)Marshal.PtrToStructure(lParam, mytype);
                this.textBox1.Text = cdata.lpData;
            }
            return IntPtr.Zero;
        }

        //WinFrom用此方法
        /* protected override void DefWndProc(ref Message m)
        {
            switch (m.Msg)
            {
            case WM_COPYDATA:
                COPYDATASTRUCT cdata = new COPYDATASTRUCT();
                Type mytype = cdata.GetType();
                cdata = (COPYDATASTRUCT)m.GetLParam(mytype);
                this.textBox1.Text = cdata.lpData;
                break;
            default:
                base.DefWndProc(ref m);
                break;
            }
        } */
    }
}

Reference documentation:

Several methods of inter-process synchronization in c# to realize communication between processes