Android Service详解(七)---绑定服务BoundService详解之Messenger双向通信的实现
作者: SuperBig 发布时间: 2019-09-12 浏览: 3451 次 编辑这是第七篇文章主要讲的是BoundService中用Messenger实现IPC。
前三篇文章对扩展Binder类和AIDL进行了说明,绑定服务一般通过AIDL和Messenger来实现IPC
一、概述
Messenger实现IPC通信,底层也是使用了AIDL方式。和AIDL方式不同的是, Messenger方式是利用Handler形式处理,因此,它是线程安全的,这也表示它不支持并发处理;而AIDL方式是非线程安全的,支持并发处理,因此,我们使用,AIDL方式时需要保证代码的线程安全。
大部分情况下, 我们应用中不需要并发处理。 因此, 我们通常只需要使用Messenger方式。
思想:在进程A中创建一个Message,将这个Message对象通过Messenger.send(message)方法传递到进程B(当然, Message对象本身是无法被传递到进程B的, send(message)方法会使用一个Parcel对象对Message对象编集,再将Parcel对象传递到进程B中,然后解编集,得到一个和进程,A中Message对象内容一样的对象) ,再把Message对象加入到进程B的消息队列里, Handler会去处理它。
二、具体步骤,双向通信的实现
1.首先创建一个Service服务,并实现一个 Handler,由其接收来自客户端的每个调用的回调
(这个是接收时的代码)
class IncomingHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case MSG_SAY_HELLO: Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show(); System.out.println(msg.getData().getString("info")); break; default: super.handleMessage(msg); } } }
(实现双向通信的代码,接收后发送给客户端)
class IncomingHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case MSG_SAY_HELLO: Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show(); System.out.println(msg.getData().getString("info")); //实现双向通讯 Messenger client = msg.replyTo; Message replyMessage = Message.obtain(null, MSG_SAY_HELLO); for(int i = 0;i<20;i++){ try { Thread.sleep(500); Bundle bundle = new Bundle(); bundle.putString("reply", "嗯嗯,我已经收到你的第"+i+"条信息,稍后回复你。"); replyMessage.setData(bundle); try { client.send(replyMessage); } catch (RemoteException e) { e.printStackTrace(); } } catch (InterruptedException e) { e.printStackTrace(); } } break; default: super.handleMessage(msg); } } }
2.Handler 用于创建 Messenger 对象(对 Handler 的引用)
final Messenger mMessenger = new Messenger(new IncomingHandler());
3.Messenger 创建一个 IBinder,服务通过 onBind() 使其返回客户端
@Override public IBinder onBind(Intent intent) { Toast.makeText(getApplicationContext(), "binding", Toast.LENGTH_SHORT).show(); return mMessenger.getBinder(); }
4.上述完整代码
public class MessengerService extends Service { /** Command to the service to display a message */ static final int MSG_SAY_HELLO = 1; /** * Handler of incoming messages from clients. */ class IncomingHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case MSG_SAY_HELLO: Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show(); System.out.println(msg.getData().getString("info")); //实现双向通讯 Messenger client = msg.replyTo; Message replyMessage = Message.obtain(null, MSG_SAY_HELLO); for(int i = 0;i<20;i++){ try { Thread.sleep(500); Bundle bundle = new Bundle(); bundle.putString("reply", "嗯嗯,我已经收到你的第"+i+"条信息,稍后回复你。"); replyMessage.setData(bundle); try { client.send(replyMessage); } catch (RemoteException e) { e.printStackTrace(); } } catch (InterruptedException e) { e.printStackTrace(); } } break; default: super.handleMessage(msg); } } } /** * Target we publish for clients to send messages to IncomingHandler. */ final Messenger mMessenger = new Messenger(new IncomingHandler()); /** * When binding to the service, we return an interface to our messenger * for sending messages to the service. */ @Override public IBinder onBind(Intent intent) { Toast.makeText(getApplicationContext(), "binding", Toast.LENGTH_SHORT).show(); return mMessenger.getBinder(); } }
5.客户端使用 IBinder 将 Messenger(引用服务的 Handler)实例化,然后使用后者将 Message 对象发送给服务
(1)定义一个Messenger对象,Messenger mService = null;并在绑定成功后实例化
public void onServiceConnected(ComponentName className, IBinder service) { // This is called when the connection with the service has been // established, giving us the object we can use to // interact with the service. We are communicating with the // service using a Messenger, so here we get a client-side // representation of that from the raw IBinder object. mService = new Messenger(service); mBound = true; }
(2)声明一个Handler用来处理服务端的数据
private class MessengerHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case MessengerService.MSG_SAY_HELLO: System.out.println("receive from Service:" + msg.getData().get("reply")); TextView textView = new TextView(getApplicationContext()); textView.setTextColor(Color.BLACK); textView.setText("receive from Service:" + msg.getData().get("reply")); linearLayout.addView(textView); break; default: super.handleMessage(msg); } } }
(3)声明一个Messenger对象
public void sayHello(View v) { if (!mBound) return; // Create and send a message to the service, using a supported 'what' value Message msg = Message.obtain(null, MessengerService.MSG_SAY_HELLO, 0, 0); Bundle bundle = new Bundle(); bundle.putString("info","呵呵哒"); msg.setData(bundle); msg.replyTo = mGetReplyMessenger; try { mService.send(msg); } catch (RemoteException e) { e.printStackTrace(); } }
并用msg.replyTo得到Messenger实例
至此绑定服务就基本结束了。
附上源码:源码
Android Service详解系列
————————————————
原文链接:https://blog.csdn.net/superbiglw/article/details/53158164