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 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);

}

}