Android也提供了封装有消息循环（Looper）的HandlerThread类，这种线程，可以绑定Handler()对象，并通过 Handler的sendMessage()函数向线程发送消息，通过handleMessage()函数，处理线程接收到的消息。这么说比较抽象，那 么，本文就利用基础的Java类库，实现一个带消息循环（Looper）的线程，以帮助初学者理解这样一个Looper到底是怎么工作的。
1. 首先，我们完成一个简单的线程框架。
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`public` `class` `LooperThread {`
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` `
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` ``private` `volatile` `boolean` `mIsLooperQuit = ``false``;`
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` `
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` ``private` `Thread mThread; `
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` `
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` ``public` `void` `start() { `
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` ``if``( mThread != ``null` `) {`
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` ``return``;`
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` ``} `
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` ``mIsLooperQuit = ``false``;`
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` ``mThread = ``new` `Thread(mLooperRunnable);`
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` ``mThread.start(); `
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` ``}`
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` `
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` ``public` `void` `stop() { `
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` ``if``( mThread == ``null` `) {`
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` ``return``;`
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` ``} `
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` ``mIsLooperQuit = ``true``;`
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` ``mThread = ``null``; `
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` ``}`
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` ``protected` `Runnable mLooperRunnable = ``new` `Runnable() { `
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` ``@Override`
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` ``public` `void` `run() {`
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` ``while``( !mIsLooperQuit ) {`
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` `
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` ``}`
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` ``}`
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` ``}; `
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`}`
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如上述代码所示，mLooperRunnable.run()循环执行线程任务，mIsLooperQuit则是线程退出循环的条件。下面，我们将添加消息的发送和处理代码。 2. 添加线程循环的消息发送和处理代码 ** ** （1） 定义消息结构体，创建消息队列 ** ** 1 <div class="line number2 index1 alt1">
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`public` `class` `LooperThread {`
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` ``private` `Queue<Message> mMessageQueue = ``new` `LinkedList<Message>();`
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` `
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` ``public` `static` `class` `Message {`
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` ``int` `what;`
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` ``} `
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`}`
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**（2） 创建互斥锁和条件变量
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`public` `class` `LooperThread {`
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` ``private` `Lock mLock = ``new` `ReentrantLock();`
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` ``private` `Condition mCondition = mLock.newCondition(); `
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`}`
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（3） 创建发送消息的函数 ** ** 1 <div class="line number2 index1 alt1">
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`//发送消息，由外部其他模块调用，发送消息给线程`
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`public` `void` `sendMessage( Message message ) {`
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` ``if``( mThread == ``null` `) {`
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` ``return``;`
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` ``} `
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` ``mLock.lock();`
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` ``mMessageQueue.add(message); ``//添加消息到消息队列`
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` ``mCondition.signal(); ``//通知线程循环，有消息来了，请立即处理`
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` ``mLock.unlock();`
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`}`
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（4） 创建处理消息的函数 ** ** 1 <div class="line number2 index1 alt1">
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`//处理消息，由线程内部调用`
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`public` `void` `handleMessage(Message message) {`
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` ``//这里可以通过一个Callback来回调监听者`
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`}`
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（5） 在mLooperRunnable.run()循环中解析消息 ** ** 1 <div class="line number2 index1 alt1">
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`protected` `Runnable mLooperRunnable = ``new` `Runnable() { `
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` `
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` ``@Override`
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` ``public` `void` `run() {`
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` `
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` ``while``( !mIsLooperQuit ) {`
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` `
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` ``mLock.lock();`
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` ``Message message = ``null``;`
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` `
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` ``try` `{`
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` ``while``( !mIsLooperQuit && mMessageQueue.isEmpty() ) {`
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` ``mCondition.await(); ``//没有消息到来则休眠`
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` ``} `
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` ``message = mMessageQueue.poll(); `
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` ``}`
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` ``catch` `(InterruptedException e) {`
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` ``e.printStackTrace(); `
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` ``}`
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` ``finally` `{`
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` ``mLock.unlock();`
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` ``} `
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` `
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` ``handleMessage(message );`
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` ``} `
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` ``}; `
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`}`
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（6） 修改线程的Stop()函数，唤醒休眠的消息循环 1 <div class="line number2 index1 alt1">
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`public` `void` `stop() { `
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` ``if``( mThread == ``null` `) {`
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` ``return``;`
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` ``} `
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` ``mIsLooperQuit = ``true``; `
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` `
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` ``mLock.lock(); `
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` ``mCondition.signal();`
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` ``mLock.unlock();`
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` `
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` ``mMessageQueue.clear();`
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` ``mThread = ``null``; `
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`}`
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到这里，一个基本的带有消息循环的线程类封装就完成了，相信大家应该从编写这段代码的过程中，理解了系统是如何实现消息循环的 附近： LooperThread 转自：http://ticktick.blog.51cto.com/823160/1565272
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