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.annotation.WorkerThread;
20import android.annotation.Nullable;
21import android.content.Intent;
22import android.os.Handler;
23import android.os.HandlerThread;
24import android.os.IBinder;
25import android.os.Looper;
26import android.os.Message;
27
28/**
29 * IntentService is a base class for {@link Service}s that handle asynchronous
30 * requests (expressed as {@link Intent}s) on demand.  Clients send requests
31 * through {@link android.content.Context#startService(Intent)} calls; the
32 * service is started as needed, handles each Intent in turn using a worker
33 * thread, and stops itself when it runs out of work.
34 *
35 * <p>This "work queue processor" pattern is commonly used to offload tasks
36 * from an application's main thread.  The IntentService class exists to
37 * simplify this pattern and take care of the mechanics.  To use it, extend
38 * IntentService and implement {@link #onHandleIntent(Intent)}.  IntentService
39 * will receive the Intents, launch a worker thread, and stop the service as
40 * appropriate.
41 *
42 * <p>All requests are handled on a single worker thread -- they may take as
43 * long as necessary (and will not block the application's main loop), but
44 * only one request will be processed at a time.
45 *
46 * <div class="special reference">
47 * <h3>Developer Guides</h3>
48 * <p>For a detailed discussion about how to create services, read the
49 * <a href="{@docRoot}guide/topics/fundamentals/services.html">Services</a> developer guide.</p>
50 * </div>
51 *
52 * @see android.os.AsyncTask
53 */
54public abstract class IntentService extends Service {
55    private volatile Looper mServiceLooper;
56    private volatile ServiceHandler mServiceHandler;
57    private String mName;
58    private boolean mRedelivery;
59
60    private final class ServiceHandler extends Handler {
61        public ServiceHandler(Looper looper) {
62            super(looper);
63        }
64
65        @Override
66        public void handleMessage(Message msg) {
67            onHandleIntent((Intent)msg.obj);
68            stopSelf(msg.arg1);
69        }
70    }
71
72    /**
73     * Creates an IntentService.  Invoked by your subclass's constructor.
74     *
75     * @param name Used to name the worker thread, important only for debugging.
76     */
77    public IntentService(String name) {
78        super();
79        mName = name;
80    }
81
82    /**
83     * Sets intent redelivery preferences.  Usually called from the constructor
84     * with your preferred semantics.
85     *
86     * <p>If enabled is true,
87     * {@link #onStartCommand(Intent, int, int)} will return
88     * {@link Service#START_REDELIVER_INTENT}, so if this process dies before
89     * {@link #onHandleIntent(Intent)} returns, the process will be restarted
90     * and the intent redelivered.  If multiple Intents have been sent, only
91     * the most recent one is guaranteed to be redelivered.
92     *
93     * <p>If enabled is false (the default),
94     * {@link #onStartCommand(Intent, int, int)} will return
95     * {@link Service#START_NOT_STICKY}, and if the process dies, the Intent
96     * dies along with it.
97     */
98    public void setIntentRedelivery(boolean enabled) {
99        mRedelivery = enabled;
100    }
101
102    @Override
103    public void onCreate() {
104        // TODO: It would be nice to have an option to hold a partial wakelock
105        // during processing, and to have a static startService(Context, Intent)
106        // method that would launch the service & hand off a wakelock.
107
108        super.onCreate();
109        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
110        thread.start();
111
112        mServiceLooper = thread.getLooper();
113        mServiceHandler = new ServiceHandler(mServiceLooper);
114    }
115
116    @Override
117    public void onStart(@Nullable Intent intent, int startId) {
118        Message msg = mServiceHandler.obtainMessage();
119        msg.arg1 = startId;
120        msg.obj = intent;
121        mServiceHandler.sendMessage(msg);
122    }
123
124    /**
125     * You should not override this method for your IntentService. Instead,
126     * override {@link #onHandleIntent}, which the system calls when the IntentService
127     * receives a start request.
128     * @see android.app.Service#onStartCommand
129     */
130    @Override
131    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
132        onStart(intent, startId);
133        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
134    }
135
136    @Override
137    public void onDestroy() {
138        mServiceLooper.quit();
139    }
140
141    /**
142     * Unless you provide binding for your service, you don't need to implement this
143     * method, because the default implementation returns null.
144     * @see android.app.Service#onBind
145     */
146    @Override
147    @Nullable
148    public IBinder onBind(Intent intent) {
149        return null;
150    }
151
152    /**
153     * This method is invoked on the worker thread with a request to process.
154     * Only one Intent is processed at a time, but the processing happens on a
155     * worker thread that runs independently from other application logic.
156     * So, if this code takes a long time, it will hold up other requests to
157     * the same IntentService, but it will not hold up anything else.
158     * When all requests have been handled, the IntentService stops itself,
159     * so you should not call {@link #stopSelf}.
160     *
161     * @param intent The value passed to {@link
162     *               android.content.Context#startService(Intent)}.
163     *               This may be null if the service is being restarted after
164     *               its process has gone away; see
165     *               {@link android.app.Service#onStartCommand}
166     *               for details.
167     */
168    @WorkerThread
169    protected abstract void onHandleIntent(@Nullable Intent intent);
170}
171