为什么用单例模式？微信就是用的单例模式

namespace Test 
{     /// <summary>    
 /// App.xaml 的交互逻辑    
 /// </summary>     
public partial class App : Application   
  {         public App()             : base()       
  {             Startup += new StartupEventHandler(App_Startup);    
     }
        private void App_Startup(object sender, StartupEventArgs e)      
   {             int times = 0;           
  bool isRun = false;         
    while (times < 5)            
 {                 
System.Diagnostics.Process[] tmp = System.Diagnostics.Process.GetProcessesByName("你的应用程序的进程名称");  
               if (tmp.Length > 1)               
  {                     System.Threading.Thread.Sleep(1000);            
         isRun = true;                 
    times++;                 }          
       else                 {               
      isRun = false;                  
   break;                 }    
         }            
 if (isRun)           
  {               
  this.Shutdown();    
         }    
     }  
   } 
}