Android中的Thread没有对java中的Thread做任何封装，而Android提供了一个遍历方法HandlerThread，他继承于Thread，实现了对遍历系统的一些封装，下面研究一下HandlerThread的源码：
/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/ package android.os; /**
* 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 {
int mPriority;
int mTid = -1;
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 overridden if needed to execute some
* setup before Looper loops.
*/
protected void onLooperPrepared() {
} @Override
public 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 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;
} /**
* Quits the handler thread's looper.
* <p>
* Causes the handler thread's looper to terminate without processing any
* more messages in the message queue.
* </p><p>
* 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.
* </p><p class="note">
* 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.
* </p>
*
* @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;
} /**
* Quits the handler thread's looper safely.
* <p>
* 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.
* </p><p>
* 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.
* </p><p>
* 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.
* </p>
*
* @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;
} /**
* Returns the identifier of this thread. See Process.myTid().
*/
public int getThreadId() {
return mTid;
}
}
下面来分析一下该类的实现原理：
1、首先该类有两个构造方法：一个传入一个字符串名称，任意选取，优先级设置为默认的，第二个多了设置进程优先级的参数
2、
实际上简单理解就是：HandlerThread可以让Handler运行于其他线程中，在平常应用中，以Activity为例，新建一个Handler对象，默认是运行于UI线程中的，如果需要在Handler中执行一些耗时的任务，可以重新开启一个子线程来执行，而不可以直接在handler中执行；
那具体用途在于哪呢？
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
为了方便描述，这里附上一段demo：
void useHanlerThread() {
// two ways to construct HandlerThread
HandlerThread hThread = new HandlerThread(”AnyName“,
// a property in android.os.Process
Process.THREAD_PRIORITY_BACKGROUND);
// HandlerThread hThread2 = new HandlerThread(”AnyName“);
hThread.start();
// get Looper object of hThread(HandlerThread)
Looper looper = hThread.getLooper();
Handler h = new Handler(looper) {
@Override
public void handleMessage(Message msg) {
// TODO Auto-generated method stub
super.handleMessage(msg);
}
};
}
由上面代码第4行可以看到，这里采用HandlerThread新建一个thread对象，实际上他就是一个Thread，只不过经过了一些封装，它封装了looper等，所以该实例也就是一个worker thread，也即新建了一个线程，只是不需要维护Looper，内部封装好了，当调用HandlerThread的start方法时，就会执行重写的run方法，进而可以直接通过第13行代码的getLooper获取，然后根据获取的这个looper来实例化Handler，这样这个Handler就工作于前面创建的HandlerThread实例中，也就是说相比传统的方式，这里可以直接处理耗时逻辑而无需再新建线程
这里再附上一段样例代码来辅助理解：
public void startWorkerHandler(){
HandlerThread handlerThread = new HandlerThread("handler-thread");
handlerThread.start();
final Handler handler = new Handler(handlerThread.getLooper());
handler.post(new Runnable() {
@Override
public void run() {
npb.increaseProgressBy(1);
handler.postDelayed(this, 100);
}
});
}
实例：
package com.example.randy.helloworld; import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper; /**
* Created by randy on 2015/12/7.
*/
public class HandlerDemo extends Activity {
private Handler handler1; private Handler handler2; private HandlerThread handlerThread;
private Handler handler3; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
handler1 = new Handler();
new Thread(new Runnable() {
@Override
public void run() {
Looper.prepare();
handler2 = new Handler();
Looper.loop();
}
}).start(); /* new Thread(new Runnable(){
@Override
public void run(){
handlerThread = new HandlerThread("handlerThread");
handlerThread.start();
}
}).start();*/ new HandlerThread("handlerThread"){ @Override
public void run(){ handler3 = new Handler();
}
}.start();
}
}