IntentService源码

Posted 2020-10-08 fankongkong

  1 /**
  2  * IntentService is a base class for {@link Service}s that handle asynchronous
  3  * requests (expressed as {@link Intent}s) on demand.  Clients send requests
  4  * through {@link android.content.Context#startService(Intent)} calls; the
  5  * service is started as needed, handles each Intent in turn using a worker
  6  * thread, and stops itself when it runs out of work.
  7  *
  8  * <p>This "work queue processor" pattern is commonly used to offload tasks
  9  * from an application‘s main thread.  The IntentService class exists to
 10  * simplify this pattern and take care of the mechanics.  To use it, extend
 11  * IntentService and implement {@link #onHandleIntent(Intent)}.  IntentService
 12  * will receive the Intents, launch a worker thread, and stop the service as
 13  * appropriate.
 14  *
 15  * <p>All requests are handled on a single worker thread -- they may take as
 16  * long as necessary (and will not block the application‘s main loop), but
 17  * only one request will be processed at a time.
 18  *
 19  * <div class="special reference">
 20  * <h3>Developer Guides</h3>
 21  * <p>For a detailed discussion about how to create services, read the
 22  * <a href="{@docRoot}guide/components/services.html">Services</a> developer
 23  * guide.</p>
 24  * </div>
 25  *
 26  * @see android.os.AsyncTask
 27  */
 28 public abstract class IntentService extends Service {
 29     private volatile Looper mServiceLooper;
 30     private volatile ServiceHandler mServiceHandler;
 31     private String mName;
 32     private boolean mRedelivery;
 33 
 34     private final class ServiceHandler extends Handler {
 35         public ServiceHandler(Looper looper) {
 36             super(looper);
 37         }
 38 
 39         @Override
 40         public void handleMessage(Message msg) {
 41             onHandleIntent((Intent)msg.obj);
 42             stopSelf(msg.arg1);
 43         }
 44     }
 45 
 46     /**
 47      * Creates an IntentService.  Invoked by your subclass‘s constructor.
 48      *
 49      * @param name Used to name the worker thread, important only for debugging.
 50      */
 51     public IntentService(String name) {
 52         super();
 53         mName = name;
 54     }
 55 
 56     /**
 57      * Sets intent redelivery preferences.  Usually called from the constructor
 58      * with your preferred semantics.
 59      *
 60      * <p>If enabled is true,
 61      * {@link #onStartCommand(Intent, int, int)} will return
 62      * {@link Service#START_REDELIVER_INTENT}, so if this process dies before
 63      * {@link #onHandleIntent(Intent)} returns, the process will be restarted
 64      * and the intent redelivered.  If multiple Intents have been sent, only
 65      * the most recent one is guaranteed to be redelivered.
 66      *
 67      * <p>If enabled is false (the default),
 68      * {@link #onStartCommand(Intent, int, int)} will return
 69      * {@link Service#START_NOT_STICKY}, and if the process dies, the Intent
 70      * dies along with it.
 71      */
 72     public void setIntentRedelivery(boolean enabled) {
 73         mRedelivery = enabled;
 74     }
 75 
 76     @Override
 77     public void onCreate() {
 78         // TODO: It would be nice to have an option to hold a partial wakelock
 79         // during processing, and to have a static startService(Context, Intent)
 80         // method that would launch the service & hand off a wakelock.
 81 
 82         super.onCreate();
 83         HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
 84         thread.start();
 85 
 86         mServiceLooper = thread.getLooper();
 87         mServiceHandler = new ServiceHandler(mServiceLooper);
 88     }
 89 
 90     @Override
 91     public void onStart(@Nullable Intent intent, int startId) {
 92         Message msg = mServiceHandler.obtainMessage();
 93         msg.arg1 = startId;
 94         msg.obj = intent;
 95         mServiceHandler.sendMessage(msg);
 96     }
 97 
 98     /**
 99      * You should not override this method for your IntentService. Instead,
100      * override {@link #onHandleIntent}, which the system calls when the IntentService
101      * receives a start request.
102      * @see android.app.Service#onStartCommand
103      */
104     @Override
105     public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
106         onStart(intent, startId);
107         return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
108     }
109 
110     @Override
111     public void onDestroy() {
112         mServiceLooper.quit();
113     }
114 
115     /**
116      * Unless you provide binding for your service, you don‘t need to implement this
117      * method, because the default implementation returns null.
118      * @see android.app.Service#onBind
119      */
120     @Override
121     @Nullable
122     public IBinder onBind(Intent intent) {
123         return null;
124     }
125 
126     /**
127      * This method is invoked on the worker thread with a request to process.
128      * Only one Intent is processed at a time, but the processing happens on a
129      * worker thread that runs independently from other application logic.
130      * So, if this code takes a long time, it will hold up other requests to
131      * the same IntentService, but it will not hold up anything else.
132      * When all requests have been handled, the IntentService stops itself,
133      * so you should not call {@link #stopSelf}.
134      *
135      * @param intent The value passed to {@link
136      *               android.content.Context#startService(Intent)}.
137      *               This may be null if the service is being restarted after
138      *               its process has gone away; see
139      *               {@link android.app.Service#onStartCommand}
140      *               for details.
141      */
142     @WorkerThread
143     protected abstract void onHandleIntent(@Nullable Intent intent);
144 }