IntentService解析

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1、源码解析

IntentService注释：

IntentService is a base class for {@link Service}s that handle asynchronousrequests (expressed as {@link Intent}s) on demand.  Clients send requeststhrough {@link android.content.Context#startService(Intent)} calls; theservice is started as needed, handles each Intent in turn using a workerthread, and stops itself when it runs out of work.

大概意思是：IntentService是基于Service的一个扩展类，主要用于处理异步请求；可以通过startService提交请求，该service在需要的时候被创建，请求是在工作线程中处理的，当完成所有任务后，该service会自动关闭。

源码：

public abstract class IntentService extends Service {    private volatile Looper mServiceLooper;    private volatile ServiceHandler mServiceHandler;    private String mName;    private boolean mRedelivery;    private final class ServiceHandler extends Handler {        public ServiceHandler(Looper looper) {            super(looper);        }        @Override        public void handleMessage(Message msg) {            onHandleIntent((Intent)msg.obj);            stopSelf(msg.arg1);        }    }    public IntentService(String name) {        super();        mName = name;    }    public void setIntentRedelivery(boolean enabled) {        mRedelivery = enabled;    }    @Override    public void onCreate() {        // TODO: It would be nice to have an option to hold a partial wakelock        // during processing, and to have a static startService(Context, Intent)        // method that would launch the service & hand off a wakelock.        super.onCreate();        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");        thread.start();        mServiceLooper = thread.getLooper();        mServiceHandler = new ServiceHandler(mServiceLooper);    }    @Override    public void onStart(Intent intent, int startId) {        Message msg = mServiceHandler.obtainMessage();        msg.arg1 = startId;        msg.obj = intent;        mServiceHandler.sendMessage(msg);    }    @Override    public int onStartCommand(Intent intent, int flags, int startId) {        onStart(intent, startId);        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;    }    @Override    public void onDestroy() {        mServiceLooper.quit();    }    @Override    public IBinder onBind(Intent intent) {        return null;    }    @WorkerThread    protected abstract void onHandleIntent(Intent intent);}

通过上面的源码阅读，可以看出，它在onCreate()中初始化了一个HandlerThread，并关联了ServiceHandler；

然后在每次调用onStartCommand()，回调了onStart()方法，通过ServiceHandler发送一个msg，消息体中包含我们的intent；最后handleMessage中回调onHandleIntent()方法，用于处理intnet事件；回调完成后调用stopSelf。

注意这个stopSelf(msg.arg1)，msg.arg1为int值，相当于一个请求的唯一标识，每发送一个请求，会生成一个唯一标识，然后将请求放入队列；当请求全部执行完成后（最后一个请求也就相当于getLasrStartId == startId）或者当前发送的标识是最近发出的那一个（getLasrStartId == startId），会销毁service。如果传入-1则直接销毁。

当service销毁会调用onDestory()，在onDestroy()中会释放Looper：mServiceLooper.quit()。

参考：

http://blog.csdn.net/lmj623565791/article/details/47143563

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