Handler消息传递机制

1. Handler消息处理类

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将Message或Runnable应用post()或sendMessage()发送到MessageQueue中，当MessageQueue循环到该Message时，调用相应的Handler对象的HandlerMessage()进行处理。

//创建Message,推荐第二种，从Message Pool直接提取，不浪费内存
Message msg = new Message();
Message msg = handler.obtainMessage();
/*发送Message的几种方式*/
//第一种
msg.what = 0x1;
Bundle bundle = new Bundle();
bundle.putString("key", "value");
msg.setData(bundle);
handler.sendMessage(msg);
//相应的提取
String str = msg.getData().getString("key");

//第二种
int what = 0x1;
handler.obtainMessage(what, "obj").sebdToTarget();
//提取
String str = msg.obj().toString();


//发送Runnable类
Runnable run = new Runnable(){...};
int delay = 1000;//毫秒
handler.post(run);//立即发送，run对象封装为Message对象
handler.postDelay(run, delay);//延时发送
handler.postAiTime(run, time);//定时发送

//消息处理回调
handler = new Handler() {
    public void handlerMessage(Message msg) {
        if (msg.what == 0x1)
        ...
    }
};

2. 非主线程中创建Handler

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需要使用Looper类的prepare()来初始化一个Looper对象

public class LooperThread extends Thread {
    public Handler handler;
    @Override
    public void run() {
        super.run();
        Looper.prepare();//初始化Looper对象
        handler = new Handler() {
            public void handlerMessage(Message msg) {}
        };
        Message msg = handler.obtainMessage();
        msg.what = 0x1;
        handler.sendMessage(msg);
        Looper.loop();//启动Looper
    }
}