public partial class App : Application  
  {  
      /// <summary>  
      /// 只打开一个进程  
      /// </summary>  
      /// <param name="e"></param>  
      protected override void OnStartup(StartupEventArgs e)  
      {  
          Process currentProcess = Process.GetCurrentProcess();  
  
          foreach (Process item in Process.GetProcessesByName(currentProcess.ProcessName))  
          {  
              if (item.Id != currentProcess.Id &&   
              (item.StartTime - currentProcess.StartTime).TotalMilliseconds <= 0)  
              {  
                  item.Kill();  
  
                  item.WaitForExit();  
  
                  break;  
              }  
          }  
  
          base.OnStartup(e);  
      }  
  }  


//csharp/6459