Android 实现点击两次返回键退出应用

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
switch (keyCode) {
case KeyEvent.KEYCODE_BACK:
long delay = Math.abs(System.currentTimeMillis() - lastBackKeyTime);
if (delay > 3000) {
// 双击退出程序
Toast toast = Toast.makeText(getApplicationContext(),
"再按一次 退出系统", Toast.LENGTH_SHORT);
toast.setGravity(Gravity.CENTER, 0, 0);
toast.show();

lastBackKeyTime = System.currentTimeMillis();
return true;
}
break;

default:
break;
}
return super.onKeyDown(keyCode, event);
}