1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.app;
18
19import android.content.Intent;
20import android.os.Handler;
21import android.os.HandlerThread;
22import android.os.IBinder;
23import android.os.Looper;
24import android.os.Message;
25
26/**
27 * IntentService is a base class for {@link Service}s that handle asynchronous
28 * requests (expressed as {@link Intent}s) on demand.  Clients send requests
29 * through {@link android.content.Context#startService(Intent)} calls; the
30 * service is started as needed, handles each Intent in turn using a worker
31 * thread, and stops itself when it runs out of work.
32 *
33 * <p>This "work queue processor" pattern is commonly used to offload tasks
34 * from an application's main thread.  The IntentService class exists to
35 * simplify this pattern and take care of the mechanics.  To use it, extend
36 * IntentService and implement {@link #onHandleIntent(Intent)}.  IntentService
37 * will receive the Intents, launch a worker thread, and stop the service as
38 * appropriate.
39 *
40 * <p>All requests are handled on a single worker thread -- they may take as
41 * long as necessary (and will not block the application's main loop), but
42 * only one request will be processed at a time.
43 *
44 * <div class="special reference">
45 * <h3>Developer Guides</h3>
46 * <p>For a detailed discussion about how to create services, read the
47 * <a href="{@docRoot}guide/topics/fundamentals/services.html">Services</a> developer guide.</p>
48 * </div>
49 *
50 * @see android.os.AsyncTask
51 */
52public abstract class IntentService extends Service {
53    private volatile Looper mServiceLooper;
54    private volatile ServiceHandler mServiceHandler;
55    private String mName;
56    private boolean mRedelivery;
57
58    private final class ServiceHandler extends Handler {
59        public ServiceHandler(Looper looper) {
60            super(looper);
61        }
62
63        @Override
64        public void handleMessage(Message msg) {
65            onHandleIntent((Intent)msg.obj);
66            stopSelf(msg.arg1);
67        }
68    }
69
70    /**
71     * Creates an IntentService.  Invoked by your subclass's constructor.
72     *
73     * @param name Used to name the worker thread, important only for debugging.
74     */
75    public IntentService(String name) {
76        super();
77        mName = name;
78    }
79
80    /**
81     * Sets intent redelivery preferences.  Usually called from the constructor
82     * with your preferred semantics.
83     *
84     * <p>If enabled is true,
85     * {@link #onStartCommand(Intent, int, int)} will return
86     * {@link Service#START_REDELIVER_INTENT}, so if this process dies before
87     * {@link #onHandleIntent(Intent)} returns, the process will be restarted
88     * and the intent redelivered.  If multiple Intents have been sent, only
89     * the most recent one is guaranteed to be redelivered.
90     *
91     * <p>If enabled is false (the default),
92     * {@link #onStartCommand(Intent, int, int)} will return
93     * {@link Service#START_NOT_STICKY}, and if the process dies, the Intent
94     * dies along with it.
95     */
96    public void setIntentRedelivery(boolean enabled) {
97        mRedelivery = enabled;
98    }
99
100    @Override
101    public void onCreate() {
102        // TODO: It would be nice to have an option to hold a partial wakelock
103        // during processing, and to have a static startService(Context, Intent)
104        // method that would launch the service & hand off a wakelock.
105
106        super.onCreate();
107        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
108        thread.start();
109
110        mServiceLooper = thread.getLooper();
111        mServiceHandler = new ServiceHandler(mServiceLooper);
112    }
113
114    @Override
115    public void onStart(Intent intent, int startId) {
116        Message msg = mServiceHandler.obtainMessage();
117        msg.arg1 = startId;
118        msg.obj = intent;
119        mServiceHandler.sendMessage(msg);
120    }
121
122    /**
123     * You should not override this method for your IntentService. Instead,
124     * override {@link #onHandleIntent}, which the system calls when the IntentService
125     * receives a start request.
126     * @see android.app.Service#onStartCommand
127     */
128    @Override
129    public int onStartCommand(Intent intent, int flags, int startId) {
130        onStart(intent, startId);
131        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
132    }
133
134    @Override
135    public void onDestroy() {
136        mServiceLooper.quit();
137    }
138
139    /**
140     * Unless you provide binding for your service, you don't need to implement this
141     * method, because the default implementation returns null.
142     * @see android.app.Service#onBind
143     */
144    @Override
145    public IBinder onBind(Intent intent) {
146        return null;
147    }
148
149    /**
150     * This method is invoked on the worker thread with a request to process.
151     * Only one Intent is processed at a time, but the processing happens on a
152     * worker thread that runs independently from other application logic.
153     * So, if this code takes a long time, it will hold up other requests to
154     * the same IntentService, but it will not hold up anything else.
155     * When all requests have been handled, the IntentService stops itself,
156     * so you should not call {@link #stopSelf}.
157     *
158     * @param intent The value passed to {@link
159     *               android.content.Context#startService(Intent)}.
160     */
161    protected abstract void onHandleIntent(Intent intent);
162}
163