今天看了IntentService的源码，终于明白它的好处了。
代码非常少，先上源码：
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);
}
}
/**
* Creates an IntentService.Invoked by your subclass's constructor.
*
* @param name Used to name the worker thread, important only for debugging.
*/
public IntentService(String name) {
super();
mName = name;
}
/**
* Sets intent redelivery preferences.Usually called from the constructor
* with your preferred semantics.
*
* <p>If enabled is true,
* {@link#onStartCommand(Intent, int, int)} will return
* {@linkService#START_REDELIVER_INTENT}, so if this process dies before
* {@link#onHandleIntent(Intent)} returns, the process will be restarted
* and the intent redelivered.If multiple Intents have been sent, only
* the most recent one is guaranteed to be redelivered.
*
* <p>If enabled is false (the default),
* {@link#onStartCommand(Intent, int, int)} will return
* {@linkService#START_NOT_STICKY}, and if the process dies, the Intent
* dies along with it.
*/
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);
}
/**
* You should not override this method for your IntentService. Instead,
* override {@link#onHandleIntent}, which the system calls when the IntentService
* receives a start request.
* @seeandroid.app.Service#onStartCommand
*/
@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();
}
/**
* Unless you provide binding for your service, you don't need to implement this
* method, because the default implementation returns null.
* @seeandroid.app.Service#onBind
*/
@Override
public IBinder onBind(Intent intent) {
return null;
}
/**
* This method is invoked on the worker thread with a request to process.
* Only one Intent is processed at a time, but the processing happens on a
* worker thread that runs independently from other application logic.
* So, if this code takes a long time, it will hold up other requests to
* the same IntentService, but it will not hold up anything else.
* When all requests have been handled, the IntentService stops itself,
* so you should not call {@link#stopSelf}.
*
* @param intent The value passed to {@link
*android.content.Context#startService(Intent)}.
*/
protected abstract void onHandleIntent(Intent intent);
}
它是将发来的Intent放到一个新线程中去处理的。对于异步的startService请求，IntentService的这个新线程会处理完第一个，再处理第二个。
这样的设计和Service有关。
先来说说Service，它有两点要说明：
1、Service不是一个进程，它和应用程序在同一个进程中；
2、Service也不是一个线程，它运行在应用程序的主线程中。
因此，一般用Service时有耗时的操作，都会将这些操作放到新启的线程中。这样的话，需要自己在Service中创建线程，而IntentService就帮我们做了这项工作。
因为大部分Service的操作都需要另启线程，也就是说大部分Service都可以用IntentService来代替。这就是IntentService的作用。
