Android HandlerThread分析

之前Handler 分析的文章有分析过，子线程Thread中是不能直接使用Handler的，需要调用Looper.prepare()方法，因此Android就为我们提供了Handler和Thread结合的方法HandlerThread方法，我们先来看下HandlerThread的源码：

public class HandlerThread extends Thread {int mPriority;int mTid = -1;Looper mLooper;private @Nullable Handler mHandler;public HandlerThread(String name) {super(name);mPriority = Process.THREAD_PRIORITY_DEFAULT;}/*** Constructs a HandlerThread.* @param name* @param priority The priority to run the thread at. The value supplied must be from* {@link android.os.Process} and not from java.lang.Thread.*/public HandlerThread(String name, int priority) {super(name);mPriority = priority;}/*** Call back method that can be explicitly overridden if needed to execute some* setup before Looper loops.*/protected void onLooperPrepared() {}@Overridepublic void run() {mTid = Process.myTid();Looper.prepare();synchronized (this) {mLooper = Looper.myLooper();notifyAll();}Process.setThreadPriority(mPriority);onLooperPrepared();Looper.loop();mTid = -1;}/*** This method returns the Looper associated with this thread. If this thread not been started* or for any reason isAlive() returns false, this method will return null. If this thread* has been started, this method will block until the looper has been initialized.* @return The looper.*/public Looper getLooper() {if (!isAlive()) {return null;}// If the thread has been started, wait until the looper has been created.synchronized (this) {while (isAlive() && mLooper == null) {try {wait();} catch (InterruptedException e) {}}}return mLooper;}/*** @return a shared {@link Handler} associated with this thread* @hide*/@NonNullpublic Handler getThreadHandler() {if (mHandler == null) {mHandler = new Handler(getLooper());}return mHandler;}public boolean quit() {Looper looper = getLooper();if (looper != null) {looper.quit();return true;}return false;}public boolean quitSafely() {Looper looper = getLooper();if (looper != null) {looper.quitSafely();return true;}return false;}/*** Returns the identifier of this thread. See Process.myTid().*/public int getThreadId() {return mTid;}
}

很简单的源码HandlerThread继承Thread主要看：

@Overridepublic void run() {mTid = Process.myTid();Looper.prepare();//手动为子线程创建了loopersynchronized (this) {mLooper = Looper.myLooper();notifyAll();}Process.setThreadPriority(mPriority);onLooperPrepared();Looper.loop();//开始轮询mTid = -1;}

可以看到run方法中为子线程创建了looper，并把对象放到线程中，然后通过Looper.loop();开启循环消息。

其他方法：

getThreadHandler：获取当前线程的handler

quit:清空所有消息

quitSafely:只情况延时消息

getLooper：获取线程中的looper对象

我们看下HandlerThread的使用：

private void startThread(){HandlerThread handlerThread = new HandlerThread("thread_one");handlerThread.start();workHandler = new Handler(handlerThread.getLooper()){//子线程handler@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);try {Thread.sleep(1000);//子线程中处理耗时操作mainHandler.sendEmptyMessage(0);//处理完后发送消息给主线程更新UI}catch (Exception e){}}};workHandler.sendEmptyMessage(0);mainHandler = new Handler(){//主线程handler@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);mBtn.setText("start");//主线程中更新UI}};
}

例子中我们看到我们通过handlerThread.getLooper()获取子线程的looper然后与workHandler，我们知道handler的线程是依赖与与之关联的looper线程，所以workHandler是子线程的handler.

然后我们new 一个未传looper的handler，默认与主线程关联，所以mainHandler是主线程的handler.

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