Herald.MainPage.HardwareButtons_BackPressed C# (CSharp) Метод

        async void HardwareButtons_BackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
          {
              e.Handled = true; // We've handled this button press
              if (!IsExit)
              {
                  //ExitSB.Begin(); 
                  IsExit = true;
                   if(dt == null)
                  {
                    dt = new DispatcherTimer();
                  }                
                  dt.Interval = TimeSpan.FromSeconds(2);
                  dt.Tick += timer_Tick;
                  dt.Start();
              }
              else
              {
                  App.Current.Exit(); 
              } 
          }
        void timer_Tick(object sender, object e)