HandlerThread使用解析

背景

以前 android 异步可以用 Handler 和 Thread配合使用，然后在run方法中调用Looper.prepare()和Looper.loop()两个方法。默认情况下android中的新的线程是没有开启消息循环，除了主线程外，主线程会自动创建Looper，开启循环消息。

HandlerThread 是继承Thread，实际上也是一个线程。然后重写run方法，在run方法中实现Looper.prepare()和Looper.loop()方法。

源码

run 方法重写：

@Override
public void run() {
    mTid = Process.myTid();
    Looper.prepare();
    synchronized (this) {
        mLooper = Looper.myLooper();
        notifyAll();
    }
    Process.setThreadPriority(mPriority);
    onLooperPrepared();
    Looper.loop();
    mTid = -1;
}

并且还提供一个getLooper方法返回HandlerThread的Lopper对象。

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;
}

除此之外还提供两个退出消息队列的方法：quit()和quitSafely()：

public boolean quit() {
    Looper looper = getLooper();
    if (looper != null) {
        looper.quit();
        return true;
    }
    return false;
}

public boolean quitSafely() {
    Looper looper = getLooper();
    if (looper != null) {
        looper.quitSafely();
        return true;
    }
    return false;
}

这两个相同点是： 不接受新的Message加入消息队列中。

• quit： 最后调用removeAllFutureMessagesLocked(),该方法的作用是把MessageQueue消息池中所有的消息全部清空，无论是延迟消息（延迟消息是指通过sendMessageDelayed或通过postDelayed等方法发送的需要延迟执行的消息）还是非延迟消息。
• quitSafely: 最后调用removeAllFutureMessagesLocked()，该方法只会清空MessageQueue消息池中所有的延迟消息，并将消息池中所有的非延迟消息派发出去让Handler去处理，quitSafely相比于quit方法安全之处在于清空消息之前会派发所有的非延迟消息。

实例

处理Message的Handler：

private Handler mMsgHandler = new Handler(){
    @Override
    public void handleMessage(Message msg) {
        switch (msg.what){
            case MSG_ONE:
                int progress = msg.arg1;
                mBar.setProgress(progress);
                mText.setText(progress + "%");
                break;
        }
    }
};

创建mHandlerThread：

mHandlerThread = new HandlerThread("handler_thread");
    mHandlerThread.start();
    //将mHandlerThread的Looper关联到主线程的Handler。
    mHandler = new Handler(mHandlerThread.getLooper());
    mHandler.post(new Runnable() {
        @Override
        public void run() {
            boolean isRunning = false;
            int count = 0;
            try {
                isRunning = true;
                count = 0;
                while (isRunning){
                    count++;
                    if(count >= 100){
                        isRunning = false;
                    }
                    Message message = Message.obtain();
                    message.what = MSG_ONE;
                    message.arg1 = count;

                    mMsgHandler.sendMessage(message);
                    Thread.sleep(1000);
                }

            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    });

完全代码

public class HandlerThreadActivity extends BaseActivity {

    private static final int MSG_ONE = 1;

    private Button mBtn;
    private TextView mText;
    private ProgressBar mBar;

    private Handler mHandler;
    private HandlerThread mHandlerThread;
    private Handler mMsgHandler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what){
                case MSG_ONE:
                    int progress = msg.arg1;
                    mBar.setProgress(progress);
                    mText.setText(progress + "%");
                    break;
            }
        }
    };

    @Override
    protected void loadViewLayout() {
        setContentView(R.layout.test_activity_handler_thread);
    }

    @Override
    protected void loadIntent() {

    }

    @Override
    protected void bindViews() {
        mBtn = (Button) findViewById(R.id.start);
        mText = (TextView) findViewById(R.id.text);
        mBar = (ProgressBar) findViewById(R.id.pba);
    }

    @Override
    protected void processLogic(Bundle savedInstanceState) {

    }

    @Override
    protected void setListener() {
        findViewById(R.id.start).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                test();
            }
        });

    }

    private void test(){
        mHandlerThread = new HandlerThread("handler_thread");
        mHandlerThread.start();
        //将mHandlerThread的Looper关联到主线程的Handler。
        mHandler = new Handler(mHandlerThread.getLooper());
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                boolean isRunning = false;
                int count = 0;
                try {
                    isRunning = true;
                    count = 0;
                    while (isRunning){
                        count++;
                        if(count >= 100){
                            isRunning = false;
                        }
                        Message message = Message.obtain();
                        message.what = MSG_ONE;
                        message.arg1 = count;

                        mMsgHandler.sendMessage(message);
                        Thread.sleep(1000);
                    }

                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

    }
}