使用Runnable和Handler做定时任务
1.定义Handler：

    Handler onlineHandler = new Handler() {        @Override        public void handleMessage(Message msg) {            super.handleMessage(msg);            switch (msg.arg1) {                case 0: {                    home_0.setImageResource(R.drawable.home_2_style);                    break;                }                case 1: {                    home_0.setImageResource(R.drawable.home_2_status_style);                    break;                }            }            home_0.postInvalidate();        }    };

   Runnable onlineRunnable = new Runnable() {        @Override        public void run() {            Message m = new Message();            if (readRd() != null && readRd().trim().equals("0")) {                m.arg1 = 0;            } else {                m.arg1 = 1;            }            onlineHandler.sendMessage(m);//每隔5秒执行一次            onlineHandler.postDelayed(onlineRunnable, 5000);        }

onlineHandler.post(onlineRunnable);