Android HandlerThread 使用介绍及简单解析

一 先看看官方介绍：

（1）HandlerThread继承自线程Thread，内部封装了有Looper。

public class HandlerThread extends Thread 

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.

（2）常用方法：

1、Looper    getLooper()//返回一个与当前线程关联的Looper
This method returns the Looper associated with this thread. 2、int getThreadId() Returns the identifier of this thread. 3、boolean quit() // HandlerThread退出资源 Quits the handler thread's looper. 4、boolean quitSafely() Quits the handler thread's looper safely. 5、void run() //执行方法（工作线程） If this thread was constructed using a separate Runnable run object, then that Runnable object's run method is called; otherwise, this method does nothing and returns.

二 HandlerThread DEMO

布局文件：

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="com.troy.handlerthreaddemo.MainActivity">

    <LinearLayout  android:id="@+id/ll_container" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical">
        <TextView  android:id="@+id/tv" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center_horizontal" android:textSize="22dp" android:layout_marginBottom="18dp" android:text="三峡日泄洪流量时刻表" />
    </LinearLayout>

</ScrollView>

MainActivity.java:

public class MainActivity extends AppCompatActivity {

    private TextView tv;
    private HandlerThread mCheckMsgThread; //HandlerThread 
    private Handler mCheckMsgHandler;   //工作线程的Handler
    private boolean isUpdateInfo;
    private static final int MSG_UPDATE_INFO = 0x110;
    private Handler mUIHandler=new Handler();//与UI线程管理的Handler
    private LinearLayout ll_container;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv=(TextView)findViewById(R.id.tv);
        ll_container=(LinearLayout)findViewById(R.id.ll_container);

        initBackThread();//创建工作线程
    }

    private void initBackThread(){
        mCheckMsgThread=new HandlerThread("check-message-coming");
        mCheckMsgThread.start();
        mCheckMsgHandler=new Handler(mCheckMsgThread.getLooper()){
            @Override
            public void handleMessage(Message msg) {
                Log.i("TEST","msg.what :"+msg.what);
                checkForUpdate();
                if(isUpdateInfo){
                    mCheckMsgHandler.sendEmptyMessageDelayed(MSG_UPDATE_INFO,1000);//自己触发自己
                }
            }
        };
    }

    private void checkForUpdate(){
        try{
            Thread.sleep(1000);
            mUIHandler.post(new Runnable() {
                @Override
                public void run() {
                    Date date=new Date();
                    DateFormat format=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                    String time=format.format(date);
                    String result="当前泄洪流量: <font color='red'>%d</font> 立方/秒 &nbsp;&nbsp;&nbsp; <font color='gray'>%s</font>";
                    result=String.format(result,(int)(Math.random()*3000+1000),time);
                    TextView textView=new TextView(MainActivity.this);
                    textView.setTextSize(20);
                    textView.setPadding(0,5,0,5);
                    textView.setText(Html.fromHtml(result));
                    ll_container.addView(textView);
                }
            });
        }catch (InterruptedException e){
            e.printStackTrace();
        }
    }

    @Override
    protected void onResume(){
        super.onResume();
        //开始查询
        isUpdateInfo = true;
        mCheckMsgHandler.sendEmptyMessage(MSG_UPDATE_INFO);
    }

    @Override
    protected void onPause(){
        super.onPause();
        //停止查询
        isUpdateInfo = false;
        mCheckMsgHandler.removeMessages(MSG_UPDATE_INFO);

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        //释放资源
        mCheckMsgThread.quit();
    }
}

运行结果如下：

三 源码分析：

HandlerThread.java：

HandlerThread的创建：

public HandlerThread(String name) {//构造方法
        super(name);
        mPriority = Process.THREAD_PRIORITY_DEFAULT;
    }

    public HandlerThread(String name, int priority) {//可设置线程优先级 int THREAD_PRIORITY_DEFAULT // 默认应用的优先级
        super(name);
        mPriority = priority;
    }

HandlerThread的启动：

@Override
    public void run() {
        mTid = Process.myTid();
        Looper.prepare();
        synchronized (this) {
            mLooper = Looper.myLooper();
            notifyAll();
        }
        Process.setThreadPriority(mPriority);//设置线程的优先级
        onLooperPrepared();
        Looper.loop();//开启消息循环
        mTid = -1;
    }

可以看到run()方法中调用了Looper.prepare()，Loop.loop();
prepare()呢，中创建了一个Looper对象，并且把该对象放到了该线程范围内的变量中（sThreadLocal），在Looper对象的构造过程中，初始化了一个MessageQueue，作为该Looper对象成员变量。loop()就开启了，不断的循环从MessageQueue中取消息处理了，当没有消息的时候会阻塞，有消息的到来的时候会唤醒。

那么，mCheckMsgThread.getLooper()做了什么：

/** * 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();//如果mLooper为空的时候，就等待，直到 mLooper = Looper.myLooper(); 由notifyAll();来唤醒；
                } catch (InterruptedException e) {
                }
            }
        }
        return mLooper;
    }

mCheckMsgThread.getLooper()返回的就是我们在run方法中创建的mLooper。

参考致谢：
1 Android HandlerThread 完全解析