一個簡單的小程式，演示了winform程式如何執行單例項。當有例項執行時，再次單擊，會啟用第一個例項。

附主要原始碼：

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;
using System.Threading;

namespace SingleInstance
{
    static class Program
    {
        public static EventWaitHandle ProgramStarted;

        /// <summary>
        /// 應用程式的主入口點。
        /// </summary>
        [STAThread]
        static void Main()
        {
            // 嘗試建立一個命名事件
            bool createNew;
            ProgramStarted = new EventWaitHandle(false, EventResetMode.AutoReset, "MyStartEvent", out createNew);

            // 如果該命名事件已經存在(存在有前一個執行例項)，則發事件通知並退出
            if (!createNew)
            {
                ProgramStarted.Set();
                return;
            }

            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());

        }

    }
}
 

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

namespace SingleInstance
{
    public partial class Form1 : Form
    {
        NotifyIcon notifyIcon1 = new NotifyIcon();

        public Form1()
        {
            InitializeComponent();

            this.notifyIcon1.Text = "Double click to show window";
            this.notifyIcon1.Icon = System.Drawing.SystemIcons.Application;
            this.notifyIcon1.DoubleClick += OnNotifyIconDoubleClicked;
            this.SizeChanged += OnSizeChanged;
            ThreadPool.RegisterWaitForSingleObject(Program.ProgramStarted, OnProgramStarted, null, -1, false);
            this.WindowState = FormWindowState.Normal;
        }

        // 當最小化時，放到系統托盤。
        void OnSizeChanged(object sender, EventArgs e)
        {
            if (this.WindowState == FormWindowState.Minimized)
            {
                this.notifyIcon1.Visible = true;
                this.Visible = false;
            }
        }

        // 當雙擊托盤圖示時，恢復視窗顯示
        void OnNotifyIconDoubleClicked(object sender, EventArgs e)
        {
            this.Visible = true;
            this.notifyIcon1.Visible = false;
            this.WindowState = FormWindowState.Normal;
        }

        // 當收到第二個程序的通知時，顯示窗體
        void OnProgramStarted(object state, bool timeout)
        {
            this.notifyIcon1.ShowBalloonTip(2000, "Hello", "I am here...", ToolTipIcon.Info);
            this.Show();
            this.WindowState = FormWindowState.Normal; //注意：一定要在窗體顯示後，再對屬性進行設定
        }
    }
}