Android中捕获回退键（back）用于提示是否退出

1.重载Activity的OnkeyDown事件

2.在里面判断两次back间隔的时间是否大于设定的时间间隔， 大于则提示，小于则直接退出。

public class MainActivity : Activity

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private DateTime _firstBackTime;

private static TimeSpan BackExitTimeSpan = new TimeSpan (0, 0, 0, 0, 800); //ms

public override bool OnKeyDown(Keycode keyCode, KeyEvent e)

{

if (e.KeyCode == Keycode .Back)

{

var secondBackTime = DateTime .Now;

if (secondBackTime - _firstBackTime > BackExitTimeSpan)

{

Toast.MakeText(_view.Context, "再按一次退出程序..." , ToastLength.Short).Show();

_firstBackTime = secondBackTime;

return true ;

}

else

{

System. Environment.Exit(0);

}

}

return base .OnKeyDown(keyCode, e);

}

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