Android连续点击两次Back键退出程序

思路1：记录上次点击的时间，与本次点击的时间比较，当两次时间间隔小于一定值时，退出，否则提示“再按一次退出程序”，同时更新上次点击时间

 private long firstTime = 0;    @Override public boolean onKeyUp(int keyCode, KeyEvent event) {        // TODO Auto-generated method stub        switch(keyCode)        {        case KeyEvent.KEYCODE_BACK:             long secondTime = System.currentTimeMillis();               if (secondTime - firstTime > 2000) {                                         //如果两次按键时间间隔大于2秒，则不退出                  Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();                   firstTime = secondTime;//更新firstTime                  return true;               } else {                                                    //两次按键小于2秒时，退出应用             System.exit(0);              }             break;        }      return super.onKeyUp(keyCode, event);    }

思路2：开线程延时处理

private int mBackKeyPressedTimes = 0;        @Override        public void onBackPressed() {                if (mBackKeyPressedTimes == 0) {                        Toast.makeText(this, "再按一次退出程序 ", Toast.LENGTH_SHORT).show();                        mBackKeyPressedTimes = 1;                        new Thread() {                                @Override                                public void run() {                                        try {                                                Thread.sleep(2000);                                        } catch (InterruptedException e) {                                                e.printStackTrace();                                        } finally {                                                mBackKeyPressedTimes = 0;                                        }                                }                        }.start();                        return;                      else{                               this.activity.finish();                            }                }                super.onBackPressed();        }

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