android -handler 实现倒计时

实现倒计时想到了三个方案
1.countDownTimer
sdk较高版本有bug 计时不精准
2.timer 和timer task的方式
但是在timertask不可以直接更新页面，还是需要用handler去更新界面。
3.handler可以用 sendEmptyMessageDelayed可以实现倒计时
而且倒计时本身没有耗时操作也不要开子线程

Handler 实现

 private static class MyHandler extends Handler {
        WeakReference<MyFragment> mWeakReference;

        MyHandler(MyFragment fragment) {
            mWeakReference = new WeakReference<>(fragment);
        }

        @Override
        public void handleMessage(Message msg) {
            final MyFragment fragment = mWeakReference.get();
            if (fragment == null)
                return;
            switch (msg.what) {
                case RESTART_COUNT_DOWN:
                    mHandler.removeCallbacksAndMessages(null);
                    fragment.countDownCount = 300;
                    sendEmptyMessage(START_COUNT_DOWN);
                    break;
                case START_COUNT_DOWN:
                    if (fragment.countDownCount > 0) {
                        String time = fragment.converterToTime(fragment.countDownCount);
                        fragment.timeTv.setText(time);
                        sendEmptyMessageDelayed(START_COUNT_DOWN, 1000);
                        fragment.countDownCount--;
                    } else {
                        sendEmptyMessage(RESTART_COUNT_DOWN);
                    }
                    break;
            }
        }
    }
//转换成 分钟：秒的形式 例如 05:00
private String converterToTime(int countDownCount) {
        int minute = countDownCount / 60;
        int second = countDownCount % 60;
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append(0);
        stringBuilder.append(minute);
        stringBuilder.append(":");
        if (second < 10) {
            stringBuilder.append(0);
        }
        stringBuilder.append(second);
        return stringBuilder.toString();
    }

fragment中调用

mHandler = new MyHandler(this);

移除所有信息

 @Override
    public void onDestroy() {
        super.onDestroy();
      
        if (mHandler != null) {
            mHandler.removeCallbacksAndMessages(null);
        }

    }