Android开发之点击两次Back键退出App

private static boolean isAppExit=false;  //定义一个变量，标示是否退出
private static Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
isAppExit = false;
}
};

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {      //重写onKeyDown()方法
// TODO Auto-generated method stub
if (keyCode==KeyEvent.KEYCODE_BACK&&event.getRepeatCount()==0) {
exit();
return true;
}
return super.onKeyDown(keyCode, event);
}

private void exit() {
if (!isAppExit) {
isAppExit = true;
Toast.makeText(getApplicationContext(), "再按一次后退键退出程序",
Toast.LENGTH_SHORT).show();
// 利用handler延迟发送更改状态信息
mHandler.sendEmptyMessageDelayed(0, 2000);
} else {
this.finish();
}
}

private long clickTime = 0; //记录第一次点击的时间
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
exit();
return true;
}
return super.onKeyDown(keyCode, event);
}

private void exit() {
if ((System.currentTimeMillis() - clickTime) > 2000) {
Toast.makeText(getApplicationContext(), "再按一次后退键退出程序",
Toast.LENGTH_SHORT).show();
clickTime = System.currentTimeMillis();
} else {
Log.e(TAG, "exit application");
this.finish();
}
}