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();             }         }     } }