public partial class App : Application

    {
        public App()
        {
            //不一定要是在Startup时,请选择适合自己应用程序的合理时间
            Startup += AppStartup;
        }
        void AppStartup(object sender, StartupEventArgs e)
        {
            bool createNew;
            var mutex = new Mutex(true, "TheIdOfThisMutex", out createNew);
            if (!createNew)
            {
                MessageBox.Show("another instance is running");
                //记得在关闭程序前关闭mutex,否则进程有可能不退出
                mutex.Close();
                //不一定要调用Shutdown方法,请选择适合自己应用程序的退出方式
                Shutdown();
            }
            else
            {
                //记得正常退出程序是关闭mutex
                Exit += delegate{ mutex.Close(); };
            }
        }
    }