Android学习之路——七.Service

Android学习之路——7.Service
这两天又学习了Android四大组件之一的Service。
继续分享我的学习历程。(*^__^*) 嘻嘻
（一）注意的细节：
（1）Service不是一个单独的Process，除非特别指派了，也不是一个Thread，但也不是运行在Main Thread中。

（2）Service的使用有两个目的，一是告诉系统要后台执行程序，一般是用Context.startService()来开启Service的（注意即使开启Service的Activity什么的destroy了，Service还是存在的，直到Context.stopService()或stopSelf()的调用），二是向其他的类，进程提供功能，这个一般是Context.bindService()来开启Service。

（3）Service的生命周期：
调用的Context.startService()   oncreate() --> onStartCommand ()--> Service is running --> The service is stopped by its or a client--> onDestroy() --> Service is shut down 
调用Context.bindService()   onBind() -->  Service is running(clients are bound to it) --> All client unbind by calling unbindService() -->onUnbind() --> onDestroy()
在Service生命周期中要注意的有：
①不管调用几次Context.startService（），即使这样导致多次调用onStartCommand()，但是一旦调用了Context.stopService() 或者stopSelf() ，这个Service就会停止。
②onStartCommand()返回一个int值，在Service类里有定义，比如START_STICKY，START_NOT_STICKY，START_REDELIVER_INTENT。
③onBind（）需要返回一个IBinder对象，以便Context和Service交互
④当Service因为系统内存低而被杀死后，系统会重启去启动它
⑤当一个有连接到Service的Context要销毁时，要调用unbindService(ServiceConnection)来断开连接

（4）当一个Service运行在前台时，必须为状态栏提供一个notification，并且这个notification一直存在直到这个Service停止或转移到后台。要让一个Service运行在前台，只要调用startForeground()方法，这个方法有两个参数，一个是唯一的标识，另一个是Notification，比如：

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, notification);

protected class BoundBinder extends Binder {/** * 返回当前Service实例，将公有方法暴露给客户端，当然也可以是其他对象 *  * @return Service实例 */BoundService getService() {return BoundService.this;}}

 /** * @see android.app.Service#onBind(android.content.Intent) */@Overridepublic IBinder onBind(Intent intent) {Log.i(TAG, TAG + " onBind");return mBind;}

private class Connection1 implements ServiceConnection {@Overridepublic void onServiceConnected(ComponentName name, IBinder service) {BoundBinder binder = (BoundBinder) service;boundService = binder.getService();//这个方法在BoundBinder类中实现mText.setText(boundService.getText());// BoundService暴露给客户端的方法stopService(boundIntent);// 停止服务unbindService(connection1);// 断开连接，记得加这句话}@Overridepublic void onServiceDisconnected(ComponentName name) {Log.i(TAG, TAG + " Contact1 onServiceDisconnected");}}

 /** * bind to a service *  * @param v */ public void bound(View v) {connection1 = new Connection1();boundIntent = new Intent(this, BoundService.class);bindService(boundIntent, connection1, BIND_AUTO_CREATE); }

 /** * 当客户端的Messenger发来Message则用这个Handler处理 这里简单的打印一句话。 * 然后通过Message绑定的Messenger对象再给客服端发送一个消息 */private Handler mHandler = new Handler() {/** * @see android.os.Handler#handleMessage(android.os.Message) */@Overridepublic void handleMessage(Message msg) {Log.i(TAG, TAG + " Handler handlemessage");Messenger m = msg.replyTo;try {m.send(Message.obtain());} catch (RemoteException e) {e.printStackTrace();}}}; private Messenger mMessenger = new Messenger(mHandler);        /** * @see android.app.Service#onBind(android.content.Intent) */@Overridepublic IBinder onBind(Intent intent) {Log.i(TAG, TAG + " onBind");return mMessenger.getBinder();}

 private class Connection2 implements ServiceConnection {/** * 向MessengerService发送一个Message，这个Message中含有当前类中的一个Messenger实例，方便MessengerService和这个类通信 *  * @see android.content.ServiceConnection#onServiceConnected(android.content.ComponentName,android.os.IBinder) */@Overridepublic void onServiceConnected(ComponentName name, IBinder service) {messenger = new Messenger(service);Message message = Message.obtain();message.replyTo = mMessenger;// 将Message的replyTo绑定到客户端定义的Messenger，以便于MessengerService向客户端发送信息try {messenger.send(message);} catch (RemoteException e) {e.printStackTrace();}}@Overridepublic void onServiceDisconnected(ComponentName name) {Log.i(TAG, TAG + " Contact2 onServiceDisconnected");}} private Handler mHandler = new Handler() {/** * 处理从MessengerService返回的Message,提示服务，断开连接 *  * @see android.os.Handler#handleMessage(android.os.Message) */@Overridepublic void handleMessage(Message msg) {Log.i(TAG, TAG + " Handler handleMessage");stopService(messengerIntent);unbindService(connection2);}};/** * 用于MessengerService向Handler发送Message的Messenger */private Messenger mMessenger = new Messenger(mHandler);

public class HelloIntentService extends IntentService {/** * A constructor is required, and must call the super IntentService(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. */@Overrideprotected 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) {}}}}}