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/components/services.html">Services</a> developer
50 * guide.</p>
51 * </div>
52 *
53 * @see android.os.AsyncTask
54 */
55public abstract class IntentService extends Service {
56    private volatile Looper mServiceLooper;
57    private volatile ServiceHandler mServiceHandler;
58    private String mName;
59    private boolean mRedelivery;
60
61    private final class ServiceHandler extends Handler {
62        public ServiceHandler(Looper looper) {
63            super(looper);
64        }
65
66        @Override
67        public void handleMessage(Message msg) {
68            onHandleIntent((Intent)msg.obj);
69            stopSelf(msg.arg1);
70        }
71    }
72
73    /**
74     * Creates an IntentService.  Invoked by your subclass's constructor.
75     *
76     * @param name Used to name the worker thread, important only for debugging.
77     */
78    public IntentService(String name) {
79        super();
80        mName = name;
81    }
82
83    /**
84     * Sets intent redelivery preferences.  Usually called from the constructor
85     * with your preferred semantics.
86     *
87     * <p>If enabled is true,
88     * {@link #onStartCommand(Intent, int, int)} will return
89     * {@link Service#START_REDELIVER_INTENT}, so if this process dies before
90     * {@link #onHandleIntent(Intent)} returns, the process will be restarted
91     * and the intent redelivered.  If multiple Intents have been sent, only
92     * the most recent one is guaranteed to be redelivered.
93     *
94     * <p>If enabled is false (the default),
95     * {@link #onStartCommand(Intent, int, int)} will return
96     * {@link Service#START_NOT_STICKY}, and if the process dies, the Intent
97     * dies along with it.
98     */
99    public void setIntentRedelivery(boolean enabled) {
100        mRedelivery = enabled;
101    }
102
103    @Override
104    public void onCreate() {
105        // TODO: It would be nice to have an option to hold a partial wakelock
106        // during processing, and to have a static startService(Context, Intent)
107        // method that would launch the service & hand off a wakelock.
108
109        super.onCreate();
110        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
111        thread.start();
112
113        mServiceLooper = thread.getLooper();
114        mServiceHandler = new ServiceHandler(mServiceLooper);
115    }
116
117    @Override
118    public void onStart(@Nullable Intent intent, int startId) {
119        Message msg = mServiceHandler.obtainMessage();
120        msg.arg1 = startId;
121        msg.obj = intent;
122        mServiceHandler.sendMessage(msg);
123    }
124
125    /**
126     * You should not override this method for your IntentService. Instead,
127     * override {@link #onHandleIntent}, which the system calls when the IntentService
128     * receives a start request.
129     * @see android.app.Service#onStartCommand
130     */
131    @Override
132    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
133        onStart(intent, startId);
134        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
135    }
136
137    @Override
138    public void onDestroy() {
139        mServiceLooper.quit();
140    }
141
142    /**
143     * Unless you provide binding for your service, you don't need to implement this
144     * method, because the default implementation returns null.
145     * @see android.app.Service#onBind
146     */
147    @Override
148    @Nullable
149    public IBinder onBind(Intent intent) {
150        return null;
151    }
152
153    /**
154     * This method is invoked on the worker thread with a request to process.
155     * Only one Intent is processed at a time, but the processing happens on a
156     * worker thread that runs independently from other application logic.
157     * So, if this code takes a long time, it will hold up other requests to
158     * the same IntentService, but it will not hold up anything else.
159     * When all requests have been handled, the IntentService stops itself,
160     * so you should not call {@link #stopSelf}.
161     *
162     * @param intent The value passed to {@link
163     *               android.content.Context#startService(Intent)}.
164     *               This may be null if the service is being restarted after
165     *               its process has gone away; see
166     *               {@link android.app.Service#onStartCommand}
167     *               for details.
168     */
169    @WorkerThread
170    protected abstract void onHandleIntent(@Nullable Intent intent);
171}
172