public MainPage()

{

HardwareButtons.BackPressed += HardwareButtons_BackPressed; //注册后退键

}

private void HardwareButtons_BackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)

{

Frame frame = Window.Current.Content as Frame;

if(frame==null)

{

return;

}

if(frame.CanGoBack)

{

frame.GoBack();

e.Handled = true;  //正常页面的推出

}

else

{

Back_Key++;//记录器
if (Back_Key == )

{

Main_Pivot.Opacity = 0.5;

Back_Text.Visibility = Visibility.Visible;

Back_Border.Visibility = Visibility.Visible;

Main_Pivot.IsEnabled = false;

DT = new DispatcherTimer();//计时器
DT.Interval = new TimeSpan(0, 0, 1)；

DT.Start();

DT.Tick += DT_Tick;

e.Handled = true;

}

else

{

App.Current.Exit();//完全退出

}

}

}