android基础知识02——线程安全4：HandlerThread-优快云博客

android的UI操作不是线程安全的，同时也只有主线程才能够操作UI，同时主线程对于UI操作有一定的时间限制（最长5秒）。为了能够做一些比较耗时的操作（比如下载、打开大文件等），android提供了一些列机制。《android基础知识02——线程安全》系列文章就是参考了网上许多网友的文章后，整理出来的一个系列，介绍了主要的方法。分别如下：

在前面介绍的线程安全中，为了操作主线程的UI，使用子线程进行处理。在android开发中，还可以使用另外两种方法进行处理：

HandlerThread

AsyncTask

本文先介绍HandlerThread。

HandlerThread继承于Thread，所以它本质就是个Thread。与普通Thread的差别就在于，它有个Looper成员变量。这个Looper其实就是对消息队列以及队列处理逻辑的封装，简单说就是消息队列+消息循环。
当我们需要一个工作者线程，而不是把它当作一次性消耗品，用过即废弃的话，就可以使用它。

其使用方法为：

public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); HandlerThread hThread=new HandlerThread("myThread"); hThread.start(); myhandler myhandler=new myhandler(hThread.getLooper()); Message msg=myhandler.obtainMessage(); msg.sendToTarget();//把 Message发送到目标对象，目标对象就是生成msg的目标对象。 } class myhandler extends Handler{ public myhandler(Looper looper){ super(looper); } public void handleMessage(Message msg) { Log.e("这是新线程", "》》》》》》》》》》》》》》》》》新线程的测试"); } }这里通过HandlerThread启动一个新线程。
注：这里需要handlerThread.start();先启动线程才能 handlerThread.getLooper() 获取当前线程的Looper。

HandlerThread使用是比较简单的，我们翻翻它的源码，也是很简单的。

/** * Handy class for starting a new thread that has a looper. The looper can then be * used to create handler classes. Note that start() must still be called. */ public class HandlerThread extends Thread { private int mPriority; private int mTid = -1; private Looper mLooper; 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 over ridden if needed to execute some * setup before Looper loops. */ protected void onLooperPrepared() { } public void run() { mTid = Process.myTid(); Looper.prepare(); synchronized (this) { mLooper = Looper.myLooper(); Process.setThreadPriority(mPriority); notifyAll(); } onLooperPrepared(); Looper.loop(); mTid = -1; } /** * This method returns the Looper associated with this thread. If this thread not been started * or for any reason is 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; } /** * Ask the currently running looper to quit. 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. */ public boolean quit() { Looper looper = getLooper(); if (looper != null) { looper.quit(); return true; } return false; } /** * Returns the identifier of this thread. See Process.myTid(). */ public int getThreadId() { return mTid; } }