handler循环刷新UI

1.新建handler及runnable对象：

    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            if(msg.what == MSG_UPDATE) {
                //todo
            }
            super.handleMessage(msg);
        }
    };

    private Runnable task = new Runnable() {
        @Override
        public void run() {
            mHandler.sendEmptyMessage(MSG_UPDATE);
            mHandler.postDelayed(this, DELAY);
        }
    };

2.启动任务及停止任务：

    @Override
    protected void onResume() {
        super.onResume();
        mHandler.postDelayed(task, DELAY);
    }

    @Override
    protected void onPause() {
        super.onPause();
        mHandler.removeCallbacks(task);
    }