Handler 01

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原创最新推荐文章于 2026-02-21 00:28:17 发布 504 阅读 AI 写同款· GEO 优化 ›

消息队列和 Looper以及源码分析 1，消息队列和Looper的工作机制 Looper 的作用就是循环遍历消息队列，如果有新消息，就把新消息交给它的目标处理。每当我们用 Handler 来发送消息，消息就会被放入消息队列中，然后 Looper 就会取出消息发送给它的目标 target。一般情况，一个消息的 target 是发送这个消息的 Handler，这么一来，Looper 就会把消息交给Handler 处理，这个时候 Handler 的 dispatchMessage 方法就会被调用，一般情况最终会调用Handler 的 handleMe 阅读详情

Handler:发送消息、处理消息对象

looper :轮训器，每个线程只能有一个Looper,决定了handler发送消息到哪个线程。new handler(Looper looper)

message:消息对象

messagequeen：消息队列

handler 创建：

//自定义 线程 +赋值给 handler
Thread t = new Thread(new Runnable() {
    @Override
    public void run() {
        Thread thread = Thread.currentThread();
        Looper.prepare();
        looper = Looper.myLooper();
        Looper.loop();//todo 写在Looper.loop()之后的代码不会被执行，这个函数内部是一个循环
    }
});
t.start();
mHandler.postDelayed(new Runnable() {
    @Override
    public void run() {
        customThreadhandler= new Handler(looper){
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                threadMethod();
            }
        };
    }
},100);

HandlerThread

本质：handler + Thread

mHandlerThread = new HandlerThread("upLoadRecordServiceHandlerThread");
mHandlerThread.start();
mHandler = new Handler(mHandlerThread.getLooper()){
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        threadMethod();
    }
};

模拟handler 开线程下载：参考：https://blog.youkuaiyun.com/u011240877/article/details/72905631

/**
* Description:
* <br> 继承 HandlerThread 模拟下载线程
*
*/

public class DownloadThread extends HandlerThread implements Handler.Callback {

private final String TAG = this.getClass().getSimpleName();
private final String KEY_URL = "url";
public static final int TYPE_START = 1;
public static final int TYPE_FINISHED = 2;

private Handler mWorkerHandler;
private Handler mUIHandler;
private List<String> mDownloadUrlList;

public DownloadThread(final String name) {
super(name);
}

@Override
protected void onLooperPrepared() { //执行初始化任务
super.onLooperPrepared();
mWorkerHandler = new Handler(getLooper(), this); //使用子线程中的 Looper
if (mUIHandler == null) {
throw new IllegalArgumentException("Not set UIHandler!");
}

//将接收到的任务消息挨个添加到消息队列中
for (String url : mDownloadUrlList) {
Message message = mWorkerHandler.obtainMessage();
Bundle bundle = new Bundle();
bundle.putString(KEY_URL, url);
message.setData(bundle);
mWorkerHandler.sendMessage(message);
}
}

public void setDownloadUrls(String... urls) {
mDownloadUrlList = Arrays.asList(urls);
}

public Handler getUIHandler() {
return mUIHandler;
}

//注入主线程 Handler
public DownloadThread setUIHandler(final Handler UIHandler) {
mUIHandler = UIHandler;
return this;
}

/**
* 子线程中执行任务，完成后发送消息到主线程
*
* @param msg
* @return
*/
@Override
public boolean handleMessage(final Message msg) {
if (msg == null || msg.getData() == null) {
return false;
}

String url = (String) msg.getData().get(KEY_URL);

//下载开始，通知主线程
Message startMsg = mUIHandler.obtainMessage(TYPE_START, "\n 开始下载 @" + DateUtils.getCurrentTime() + "\n" + url);
mUIHandler.sendMessage(startMsg);

SystemClock.sleep(2000); //模拟下载

//下载完成，通知主线程
Message finishMsg = mUIHandler.obtainMessage(TYPE_FINISHED, "\n 下载完成 @" + DateUtils.getCurrentTime() + "\n" + url);
mUIHandler.sendMessage(finishMsg);

return true;
}

@Override
public boolean quitSafely() {
mUIHandler = null;
return super.quitSafely();
}
}