WPF之单例模式

Question

1、为了实现单例模式，在App类中添加了如下代码，使用了信号量，但是为什么返回值isNew一直为true

public partial class App : Application
    {
        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);
            bool isNew=false;
            Mutex mutex = new Mutex(true, "MySingleInstance", out isNew);
            if(!isNew)
            {
                ActivateOtherWindow();
                Shutdown();
            }
            GC.KeepAlive(isNew);
        }

        private static void ActivateOtherWindow()
        {
            var other = Win32Api.FindWindow(null, "MainWindow");
            if (other != IntPtr.Zero)
            {
                Win32Api.SetForegroundWindow(other);
                if (Win32Api.IsIconic(other))
                    Win32Api.OpenIcon(other);
            }
        }
    }

Answer 1

mutex不能被回收

Answer 2

private Mutex mutex = null;

private void CheckSingleInstanceAndStartMainApp(string title)
        {
            bool isNew = false;
            if (null == mutex)
                mutex = new Mutex(true, "PowerPixel", out isNew);
            if (!isNew)
            {
                ActiveAndShowToFront(title);
                Environment.Exit(0);//强制退出，不会有弹框提示
            }
        }

        private void ActiveAndShowToFront(string titleName)
        {
            //s1:通过WAPi:FindWindow获取运行实例的句柄
            //或者事先保存实例，传递过来           
            IntPtr hwnd = Win32Api.FindWindow(null, titleName);

            if (hwnd != IntPtr.Zero)
            {
                Win32Api.SetForegroundWindow(hwnd);
                if (Win32Api.IsIconic(hwnd))
                    Win32Api.OpenIcon(hwnd);
            }
        }