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 17 package android.app; 18 19 import android.annotation.WorkerThread; 20 import android.annotation.Nullable; 21 import android.content.Intent; 22 import android.os.Handler; 23 import android.os.HandlerThread; 24 import android.os.IBinder; 25 import android.os.Looper; 26 import 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 */ 54 public 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 { ServiceHandler(Looper looper)61 public ServiceHandler(Looper looper) { 62 super(looper); 63 } 64 65 @Override handleMessage(Message msg)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 */ IntentService(String name)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 */ setIntentRedelivery(boolean enabled)98 public void setIntentRedelivery(boolean enabled) { 99 mRedelivery = enabled; 100 } 101 102 @Override onCreate()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 onStart(@ullable Intent intent, int startId)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 onStartCommand(@ullable Intent intent, int flags, int startId)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 onDestroy()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 onBind(Intent intent)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 onHandleIntent(@ullable Intent intent)169 protected abstract void onHandleIntent(@Nullable Intent intent); 170 } 171