扩展Service这是所有服务的基类。扩展这个类的时候，特别重要的一点是，需要创建一个新的线程来做服务任务，因为service默认是运行在你的主线程（UI线程）中的，它会使你的主线程运行缓慢。
扩展IntentService这是一个service的子类，他可以在一个工作线程中处理所有的启动请求。如果你不需要同一时刻出来所有的服务请求，使用IntentService是一个很好的选择。你需要做的仅仅是实现onHandlerIntent()方法，通过这个函数处理接受的每一个启动请求。
1.创建一个独立于主线程的工作线程，用于执行通过onStartCommand()传来的所有的intent。2.创建一个工作队列，将接受的所有intent一个一个的传给onHandlerIntent()，所以同一时间内你只处理一个intent，不用担心多线程的问题。3.当所有的请求都处理完后，停止服务，所以你不需要手动调用stopSelf()。4.提供onBind()函数的默认实现，返回null5.提供onStartCommand()函数的默认实现，它把intent发送到工作队列中去，然后工作队列再发送到你的onHandlerIntent()函数中。
public class HelloIntentService extends IntentService {
/**
* A constructor is required, and must call the superIntentService(String)
* constructor with a name for the worker thread.
*/
public HelloIntentService() {
super("HelloIntentService");
}
/**
* The IntentService calls this method from the default worker thread with
* the intent that started the service. When this method returns, IntentService
* stops the service, as appropriate.
*/
@Override
protected void onHandleIntent(Intent intent) {
// Normally we would do some work here, like download a file.
// For our sample, we just sleep for 5 seconds.
long endTime = System.currentTimeMillis() + 5*1000;
while (System.currentTimeMillis() < endTime) {
synchronized (this) {
try {
wait(endTime - System.currentTimeMillis());
} catch (Exception e) {
}
}
}
}
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Toast.makeText(this, "service starting", Toast.LENGTH_SHORT).show();
return super.onStartCommand(intent,flags,startId);
}
public class HelloService extends Service {
private Looper mServiceLooper;
private ServiceHandler mServiceHandler;
// Handler that receives messages from the thread
private final class ServiceHandler extends Handler {
public ServiceHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
// Normally we would do some work here, like download a file.
// For our sample, we just sleep for 5 seconds.
long endTime = System.currentTimeMillis() + 5*1000;
while (System.currentTimeMillis() < endTime) {
synchronized (this) {
try {
wait(endTime - System.currentTimeMillis());
} catch (Exception e) {
}
}
}
// Stop the service using the startId, so that we don‘t stop
// the service in the middle of handling another job
stopSelf(msg.arg1);
}
}
@Override
public void onCreate() {
// Start up the thread running the service. Note that we create a
// separate thread because the service normally runs in the process‘s
// main thread, which we don‘t want to block. We also make it
// background priority so CPU-intensive work will not disrupt our UI.
HandlerThread thread = new HandlerThread("ServiceStartArguments",
Process.THREAD_PRIORITY_BACKGROUND);
thread.start();
// Get the HandlerThread‘s Looper and use it for our Handler
mServiceLooper = thread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Toast.makeText(this, "service starting", Toast.LENGTH_SHORT).show();
// For each start request, send a message to start a job and deliver the
// start ID so we know which request we‘re stopping when we finish the job
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
mServiceHandler.sendMessage(msg);
// If we get killed, after returning from here, restart
return START_STICKY;
}
@Override
public IBinder onBind(Intent intent) {
// We don‘t provide binding, so return null
return null;
}
@Override
public void onDestroy() {
Toast.makeText(this, "service done", Toast.LENGTH_SHORT).show();
}
}
START_NOT_STICKY在onStartCommand()返回后，系统杀死服务，服务将不会重启，除非有pending intents（目前笔者还不懂什么是pending Intents）要投递。这比较适合非常容易就可以重新启动未完成任务的情况。
START_STICKY在系统杀死服务后，重启服务并且调用onStartCommand()，但是不重新投递上一次的intent。系统会传给onStartCommand()函数null，除非有pending intent来启动服务，会传给onStartCommand()相应的intent。这种做法比较适合媒体播放服务，不需要执行命令，但是独立运行，常处于等待任务的服务。
START_REDELIVER_INTENT在系统杀死服务后，重启服务并且调用onStartCommand()，参数传入上一次的intent，然后接下来是pending intent传入onStartCommand()。这比较适合于正在执行一项工作，它不能被立刻恢复，例如下载文件。
Intent intent = new Intent(this, HelloService.class);
startService(intent);
Notification notification = new Notification(R.drawable.icon, getText(R.string.ticker_text),
System.currentTimeMillis());
Intent notificationIntent = new Intent(this, ExampleActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0);
notification.setLatestEventInfo(this, getText(R.string.notification_title),
getText(R.string.notification_message), pendingIntent);
startForeground(ONGOING_NOTIFICATION_ID, notification);
原文：http://blog.csdn.net/oracleot/article/details/18817087