一、Handler 常用用法

主线程 Handler 主要作用 :Looper 和 Message 都在主线程 , Handler 也在主线程初始化 , 在子线程中调用该 Handler , 通知主线程进行一些操作 , 一般是更新 UI ;

子线程 Handler 主要作用 :Looper 和 Message 都在子线程 , Handler 也在子线程初始化 , 在主线程中调用该 Handler , 通知子线程进行一些操作 , 一般是网络操作 , 计算 , 或其它耗时任务 ;

二、HandlerThread 简介

HandlerThread 就是使用了 Handler 机制的线程 , 其本质是一个线程 Thread ; 属于上述介绍的子线程 Handler 机制 ;

在运行 HandlerThread 线程的 run 方法时 ,

在 run 方法开始处 , 会调用 Looper.prepare() 方法 , 初始化该线程的 Looper ,

在 run 方法结束处 , 会调用 Looper.loop() 方法 , 开启无限循环 , 从 Looper 中的 MessageQueue 中循环获取消息 , 并转发给取出的 Message 消息对应的 Handler 进行相关任务处理 ;

HandlerThread 线程的 run() 方法如下 :

public class HandlerThread extends Thread {@Overridepublic void run() {mTid = Process.myTid();Looper.prepare();synchronized (this) {mLooper = Looper.myLooper();notifyAll();}Process.setThreadPriority(mPriority);onLooperPrepared();Looper.loop();mTid = -1;}}

三、HandlerThread 源码

/*** 含有 Looper 的线程.* Looper 用于创建 Handler.* * 该类是一个线程类, 必须调用 start 方法开启线程. */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;}/*** 创建 HandlerThread.* @param name* @param priority 线程运行优先级*/public HandlerThread(String name, int priority) {super(name);mPriority = priority;}/*** Looper 无限循环之前执行的操作 */protected void onLooperPrepared() {}@Overridepublic void run() {mTid = Process.myTid();// Looper 初始化 Looper.prepare();synchronized (this) {mLooper = Looper.myLooper();notifyAll();}Process.setThreadPriority(mPriority);onLooperPrepared();// 无限循环获取消息并执行Looper.loop();mTid = -1;}/*** 返回与该线程关联的 Looper .* 如果线程没有启动 , 或者线程不处于活动状态 , 返回空.* 如果线程已经启动 , 该方法会阻塞 , 直到 Looper 被初始化完毕后 , 返回 Looper.* @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 返回一个与该线程关联的共享 Handler* @hide*/@NonNullpublic Handler getThreadHandler() {if (mHandler == null) {mHandler = new Handler(getLooper());}return mHandler;}/*** 退出 Looper 循环. * * Causes the handler thread's looper to terminate without processing any* more messages in the message queue.* * Any attempt to post messages to the queue after the looper is asked to quit will fail.* For example, the {@link Handler#sendMessage(Message)} method will return false.* * Using this method may be unsafe because some messages may not be delivered* before the looper terminates. Consider using {@link #quitSafely} instead to ensure* that all pending work is completed in an orderly manner.* ** @return True if the looper looper has been asked to quit or false if the* thread had not yet started running.** @see #quitSafely*/public boolean quit() {Looper looper = getLooper();if (looper != null) {looper.quit();return true;}return false;}/*** 安全退出线程 loop.* * Causes the handler thread's looper to terminate as soon as all remaining messages* in the message queue that are already due to be delivered have been handled.* Pending delayed messages with due times in the future will not be delivered.* * Any attempt to post messages to the queue after the looper is asked to quit will fail.* For example, the {@link Handler#sendMessage(Message)} method will return false.* * If the thread has not been started or has finished (that is if* {@link #getLooper} returns null), then false is returned.* Otherwise the looper is asked to quit and true is returned.* ** @return True if the looper looper has been asked to quit or false if the* thread had not yet started running.*/public boolean quitSafely() {Looper looper = getLooper();if (looper != null) {looper.quitSafely();return true;}return false;}/*** 返回线程 ID*/public int getThreadId() {return mTid;}}

【Android 异步操作】Handler 机制 ( Handler 常用用法 | HandlerThread 简介 | HandlerThread 源码注释分析 )