Android中HandlerThread种的解析_Android

Android中HandlerThread类的解析

Android应用中的消息循环由Looper和Handler配合完成，Looper类用于封装消息循环，类中有个MessageQueue消息队列；Handler类封装了消息投递和消息处理等功能。

系统默认情况下只有主线程（即UI线程）绑定Looper对象，因此在主线程中可以直接创建Handler的实例，但是在子线程中就不能直接new出Handler的实例了，因为子线程默认并没有Looper对象，此时会抛出RuntimeException异常：

浏览下Handler的默认构造函数就一目了然了：

    public Handler() {        if (FIND_POTENTIAL_LEAKS) {            final Class<? extends Handler> klass = getClass();            if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) &&                    (klass.getModifiers() & Modifier.STATIC) == 0) {                Log.w(TAG, "The following Handler class should be static or leaks might occur: " +                    klass.getCanonicalName());            }        }        mLooper = Looper.myLooper();        if (mLooper == null) {            throw new RuntimeException(                "Can't create handler inside thread that has not called Looper.prepare()");        }        mQueue = mLooper.mQueue;        mCallback = null;    }

如果需要在子线程中使用Handler类，首先需要创建Looper类实例，这时可以通过Looper.prepare()和Looper.loop()函数来实现的。阅读Framework层源码发现，Android为我们提供了一个HandlerThread类，该类继承Thread类，并使用上面两个函数创建Looper对象，而且使用wait/notifyAll解决了多线程中子线程1获取子线程2的Looper对象为空的问题。HandlerThread类完整代码如下：

/** * 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; // 线程优先级		private int mTid = -1; // 线程ID		private Looper mLooper; // 我们需要的Looper对象	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 [email protected] android.os.Process} and not from java.lang.Thread.	 */	public HandlerThread(String name, int priority) {		super(name);		mPriority = priority;	}	/**	 * 在Looper.loop()之前执行动作的回调函数	 */	protected void onLooperPrepared() {	}	public void run() {		mTid = Process.myTid();		Looper.prepare(); // 创建本线程的Looper对象				synchronized (this) {			mLooper = Looper.myLooper();			notifyAll(); //通知所有等待该线程Looper对象的其他子线程，本线程的Looper对象已就绪		}				Process.setThreadPriority(mPriority);		onLooperPrepared(); //回调函数				Looper.loop(); //开始消息队列循环		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(); //Looper对象未创建好，等待				} 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 [email protected] #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;	}}

2楼zhyl8157121昨天 12:57: 同问，这种黑底的怎么弄的

1楼fengqiangfeng昨天 08:59: 楼主的eclipse皮肤是哪一种，求指导