C#中只启动一个程序实例

        当我们需要只启动一个C#程序实例的时候，一个比较标准的做法是，在程序入口使用一个互斥量来判断是否本程序已经启动，如果程序已经启动则将已经启动的程序激活。代码如下（以WPF为例）：

App.xaml:

<Application x:Class="TestOneInstanceOnly.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Application.Resources>
    </Application.Resources>
</Application>

App.xaml.cs:

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Threading;
using System.Windows;

namespace TestOneInstanceOnly
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        static extern bool SetForegroundWindow(IntPtr hWnd);

        private readonly string _appId = "a03484f1-7423-4faa-878a-a9eef271780d";

        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);
            if (IsExists())
            {
                var currentProcess = Process.GetCurrentProcess();

                foreach (var process in Process.GetProcessesByName(currentProcess.ProcessName))
                {
                    if (process.Id != currentProcess.Id)
                    {
                        SetForegroundWindow(process.MainWindowHandle);
                        break;
                    }
                }

                Shutdown(1);
                return;
            }

            StartupUri = new Uri("MainWindow.xaml", UriKind.Relative);
        }

        private static Mutex _mutex;//避免被作为垃圾回收。

        /// <summary>
        /// 使用互斥量判断程序是否已经运行。
        /// </summary>
        /// <returns>已经运行返回true，否则返回false。</returns>
        internal bool IsExists()
        {
            bool creatNew;
            _mutex = new Mutex(true, _appId, out creatNew);
            if (creatNew)
            {
                GC.KeepAlive(_mutex);
                return false;
            }

            return true;
        }
    }
}

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