Android HandlerThread 详解

文章出处：https://blog.csdn.net/shift_wwx/article/details/49666749

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之前 Android 中Handler 中大体说了一下handler的应用过程，为了更好实现异步操作，android 提供了HandlerThread。

/** * 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;    }

说白了就是个Thread，但是在这里直接将Looper 给弄好了：

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

所以，在新建实例之后，必须要start 才能能应用，不然在getLooper的时候：

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;}

会认为不是alive，返回null。

所以一般应用过程是这样的：

//创建一个HandlerThread，即创建了一个包含Looper的线程。    HandlerThread handlerThread = new HandlerThread("leochin.com");    handlerThread.start(); //创建HandlerThread后一定要记得start()//获取HandlerThread的Looper    Looper looper = handlerThread.getLooper();//创建Handler，通过Looper初始化    Handler handler = new Handler(looper);

这个handler 就不在UI线程，这样就可以实现了异步操作，至于发msg 还是 post 就在UI 现在操作就可以了。

弄个例子（copy 于Android TV）：

    public TvInputBaseSession(Context context, String inputId, int deviceId) {        super(context);        mInputId = inputId;        mDeviceId = deviceId;        mTvInputManager = (TvInputManager)context.getSystemService(Context.TV_INPUT_SERVICE);        mHardware = mTvInputManager.acquireTvInputHardware(deviceId,                mHardwareCallback, mTvInputManager.getTvInputInfo(inputId));        initThread(mInputId);    }    private void initThread(String inputId) {        mHandlerThread = new HandlerThread(inputId);        mHandlerThread.start();        mSessionHandler = new Handler(mHandlerThread.getLooper(), this);    }    private void releaseThread() {        mHandlerThread.quit();        mHandlerThread = null;        mSessionHandler = null;    }    @Override    public boolean handleMessage(Message msg) {        if (DEBUG)            Log.d(TAG, "==== handleMessage ====" + msg.what);        switch (msg.what) {            case DroidLogicTvUtils.SESSION_DO_RELEASE:                doRelease();                break;            default:                break;        }        return false;    }    public void doRelease() {        mHardware.setSurface(null, null);        mTvInputManager.releaseTvInputHardware(mDeviceId, mHardware);        releaseThread();    }    @Override    public void onRelease() {        mSessionHandler.obtainMessage(DroidLogicTvUtils.SESSION_DO_RELEASE).sendToTarget();    }

Android TV 中要求有些操作时间不能过长，例如onRelease，通过这样的操作就成功避免了

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