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.content.Intent; 20 import android.os.Handler; 21 import android.os.HandlerThread; 22 import android.os.IBinder; 23 import android.os.Looper; 24 import 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 */ 52 public 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 { ServiceHandler(Looper looper)59 public ServiceHandler(Looper looper) { 60 super(looper); 61 } 62 63 @Override handleMessage(Message msg)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 */ IntentService(String name)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 */ setIntentRedelivery(boolean enabled)96 public void setIntentRedelivery(boolean enabled) { 97 mRedelivery = enabled; 98 } 99 100 @Override onCreate()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 onStart(Intent intent, int startId)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 onStartCommand(Intent intent, int flags, int startId)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 onDestroy()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 onBind(Intent intent)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 */ onHandleIntent(Intent intent)161 protected abstract void onHandleIntent(Intent intent); 162 } 163