在winform下，只运行一个实例只需这样就可以：

1． 首先要添加如下的namespace：

using System.Threading;

2． 修改系统Main函数，大致如下：

        bool bCreatedNew;      

        //Create a new mutex using specific mutex name

        Mutex m =new Mutex( false, "myUniqueName", out bCreatedNew );

        if( bCreatedNew )

            Application.Run(new yourFormName());

在wpf中如何做呢？

我在微软论坛发帖之后，有高手提出了如下的解决办法，我试验之后，此法可行，就贴出来和大家分享。有人还有其他解决办法，可以写出来一起探讨：

首先 引用Microsoft.VisualBasic 然后新建一个类 single public  class single:Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase     {
         App a; public single()        {
  this.IsSingleInstance = true;        } protected override bool OnStartup(Microsoft.VisualBasic.ApplicationServices.StartupEventArgs eventArgs)        {
             a = new App();            a.InitializeComponent();            a.Run(); return false;        } protected override void OnStartupNextInstance(Microsoft.VisualBasic.ApplicationServices.StartupNextInstanceEventArgs eventArgs)        {
  base.OnStartupNextInstance(eventArgs);            a.activate();        }     } app.cs public partial class App : Application     {
  protected override void OnStartup(StartupEventArgs e)         {
  base.OnStartup(e);             Window1 w = new Window1();             w.Show();         } public void activate()         {
              MainWindow.Activate();         } private void Application_SessionEnding(object sender, SessionEndingCancelEventArgs e)         {
          } private void Application_Startup(object sender, StartupEventArgs e)         {
          } private void Application_Exit(object sender, ExitEventArgs e)         {
          }     } app.g.cs         [System.STAThreadAttribute()]         [System.Diagnostics.DebuggerNonUserCodeAttribute()] public static void Main(string [] a ) {
              single s = new single();             s.Run(a);           }