Android中AIDL实现进程通信.doc

Android中AIDL实现进程通信之前的文章演示了如何通过Messenger实现与Service进行跨进程通信，即IPC。但用Messenger实现的IPC存在一点不足：Service内部维护着一个Messenger，Messenger内部又维护着一个Hanlder，当多个client向该Service发送Message时，这些Message需要依次进入Hanlder的消息队列中，Hanlder只能处理完一个Message之后，再从消息队列中取出下一个进行处理，这样Service相当于只能对客户端传来的Message进行串行执行，而不能并行执行。如果想让Service跨进程并发处理客户端发来的请求，那么就需要使用AIDL。AIDL的全称是Android Interface Definition Language，直译过来就是Android接口定义语言。在Android中，正常情况下，不同进程是不能互相访问对方的内存数据的。为了实现进程间内存访问，可以将一个进程中的内存数据分解成Android认识的原子类型，然后在另一个进程中将原子类型的数据重新组合成对象。编写将原子类型的数据重新组合成对象的代码比较费时，Android通过AIDL可以实现该功能。其实Messenger和AIDL并不是对立的，Messenger内部也是基于AIDL实现的。当使用Messenger的时候，Service会用一个Handler串行执行客户端发来的多个请求，即单线程处理；当直接使用AIDL的时候，Service会维护一个线程池，用该线程池并发处理客户端发来的多个请求。再次强调一下，如果你想实现跨进程通信，但是并不关注多线程并发处理，那么你只需要使用Messenger即可，无需编写AIDL代码，只有当你想让Service并发处理客户端的请求的时候，才需要编写AIDL代码。AIDL之Service端实现使用AIDL的典型案例就是一个App的Activity启动了一个Service，并且让该Service运行在一个新的进程中，这种在新进程中的Service我们可以叫做远程Service，该Service会从服务器拿到最新的数据，客户端可以调用Service相应的方法获得最新数据，更近一步的话，Service拿到最新数据之后可以主动向客户端发送。要想使用AIDL，要同时在Service和client都编写相应的代码。在Service端，首先要创建.aidl文件，然后需要实现.aidl中定义的各种方法。具体如下：首先要创建.aidl文件在Android Studio中右键创建AIDL文件，该文件其实就是定义一个接口Interface，和定义一般的Java接口差不多，需要在该接口中定义一些方法，这些方法就是允许客户端跨进程调用的方法，我创建了IRemoteService.aidl文件，如下所示：/ IRemoteInterface.aidlpackage com.ispring.aidldemo;import com.ispring.aidldemo.IRemoteInterfaceCallback;interface IRemoteInterface /获取Service运行的进程ID int getPid(); /从Service中获取最新的数据 int getData(); /通过向Service中注册回调，可以实现Service主动向客户端推送数据 void registerCallback(IRemoteInterfaceCallback cb); /删除注册的回调 void unregisterCallback(IRemoteInterfaceCallback cb);我们在上面的.aidl文件中，定义了四个方法供客户端调用，通过getPid()方法，可以获取Service运行的进程ID；通过getData()方法，可以让客户端从Service获取最新的数据；registerCallback和unregisterCallback是用来进行注册、反注册客户端回调的，后面会详细解释。AIDL中定义的方法可以接受如下的参数类型作为形参：所有的基本类型，例如int, long, char, boolean等等String、CharSequence、List、Map在编写完上述IRemoteInterface.aidl文件后，我们编译一下Project，Android Studio会自动帮我们生成一个IRemoteInterface.java文件，如下所示（对于下面的代码，我们无需关注具体实现，大家了解一下即可）：/* * This file is auto-generated. DO NOT MODIFY. * Original file: D:iWorkAndroidStudioProjectsAidlDemoappsrcmainaidlcomispringaidldemoIRemoteInterface.aidl */package com.ispring.aidldemo;public interface IRemoteInterface extends android.os.IInterface /* Local-side IPC implementation stub class. */ public static abstract class Stub extends android.os.Binder implements com.ispring.aidldemo.IRemoteInterface private static final java.lang.String DESCRIPTOR = com.ispring.aidldemo.IRemoteInterface; /* Construct the stub at attach it to the interface. */ public Stub() this.attachInterface(this, DESCRIPTOR); /* * Cast an IBinder object into an com.ispring.aidldemo.IRemoteInterface interface, * generating a proxy if needed. */ public static com.ispring.aidldemo.IRemoteInterface asInterface(android.os.IBinder obj) if (obj=null) return null; android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR); if (iin!=null)&(iin instanceof com.ispring.aidldemo.IRemoteInterface) return (com.ispring.aidldemo.IRemoteInterface)iin); return new com.ispring.aidldemo.IRemoteInterface.Stub.Proxy(obj); Override public android.os.IBinder asBinder() return this; Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException switch (code) case INTERFACE_TRANSACTION: reply.writeString(DESCRIPTOR); return true; case TRANSACTION_getPid: data.enforceInterface(DESCRIPTOR); int _result = this.getPid(); reply.writeNoException(); reply.writeInt(_result); return true; case TRANSACTION_getData: data.enforceInterface(DESCRIPTOR); int _result = this.getData(); reply.writeNoException(); reply.writeInt(_result); return true; case TRANSACTION_registerCallback: data.enforceInterface(DESCRIPTOR); com.ispring.aidldemo.IRemoteInterfaceCallback _arg0; _arg0 = com.ispring.aidldemo.IRemoteInterfaceCallback.Stub.asInterface(data.readStrongBinder(); this.registerCallback(_arg0); reply.writeNoException(); return true; case TRANSACTION_unregisterCallback: data.enforceInterface(DESCRIPTOR); com.ispring.aidldemo.IRemoteInterfaceCallback _arg0; _arg0 = com.ispring.aidldemo.IRemoteInterfaceCallback.Stub.asInterface(data.readStrongBinder(); this.unregisterCallback(_arg0); reply.writeNoException(); return true; return super.onTransact(code, data, reply, flags); private static class Proxy implements com.ispring.aidldemo.IRemoteInterface private android.os.IBinder mRemote; Proxy(android.os.IBinder remote) mRemote = remote; Override public android.os.IBinder asBinder() return mRemote; public java.lang.String getInterfaceDescriptor() return DESCRIPTOR; Override public int getPid() throws android.os.RemoteException android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); int _result; try _data.writeInterfaceToken(DESCRIPTOR); mRemote.transact(Stub.TRANSACTION_getPid, _data, _reply, 0); _reply.readException(); _result = _reply.readInt(); finally _reply.recycle(); _data.recycle(); return _result; Override public int getData() throws android.os.RemoteException android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); int _result; try _data.writeInterfaceToken(DESCRIPTOR); mRemote.transact(Stub.TRANSACTION_getData, _data, _reply, 0); _reply.readException(); _result = _reply.readInt(); finally _reply.recycle(); _data.recycle(); return _result; Override public void registerCallback(com.ispring.aidldemo.IRemoteInterfaceCallback cb) throws android.os.RemoteException android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); try _data.writeInterfaceToken(DESCRIPTOR); _data.writeStrongBinder(cb!=null)?(cb.asBinder():(null); mRemote.transact(Stub.TRANSACTION_registerCallback, _data, _reply, 0); _reply.readException(); finally _reply.recycle(); _data.recycle(); Override public void unregisterCallback(com.ispring.aidldemo.IRemoteInterfaceCallback cb) throws android.os.RemoteException android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); try _data.writeInterfaceToken(DESCRIPTOR); _data.writeStrongBinder(cb!=null)?(cb.asBinder():(null); mRemote.transact(Stub.TRANSACTION_unregisterCallback, _data, _reply, 0); _reply.readException(); finally _reply.recycle(); _data.recycle(); static final int TRANSACTION_getPid = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0); static final int TRANSACTION_getData = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1); static final int TRANSACTION_registerCallback = (android.os.IBinder.FIRST_CALL_TRANSACTION + 2); static final int TRANSACTION_unregisterCallback = (android.os.IBinder.FIRST_CALL_TRANSACTION + 3); public int getPid() throws android.os.RemoteException; public int getData() throws android.os.RemoteException; public void registerCallback(com.ispring.aidldemo.IRemoteInterfaceCallback cb) throws android.os.RemoteException; public void unregisterCallback(com.ispring.aidldemo.IRemoteInterfaceCallback cb) throws android.os.RemoteException;对于上面的代码，我们无需关注具体实现，我们只需要知道以下几点即可：IRemoteInterface.java中，定义了名为IRemoteInterface的interface，其对应着IRemoteInterface.aidl定义的接口，囊括了IRemoteInterface.aidl中定义的方法。IRemoteInterface继承自android.os.IInterface，如下所示：public interface IRemoteInterface extends android.os.IInterfaceIRemoteInterface接口中有一个静态内部类Stub。Stub是个抽象类，继承自android.os.Binder，且实现了IRemoteInterface接口，如下所示：public static abstract class Stub extends android.os.Binder implements com.ispring.aidldemo.IRemoteInterfaceSub类中有一个asInterface方法，该方法非常重要，其接收一个android.os.IBinder类型的对象，返回IRemoteInterface类型，其方法签名如下定义：public static com.ispring.aidldemo.IRemoteInterface asInterface(android.os.IBinder obj)实现AIDL所定义的接口我们定义了一个RemoteService类，其继承自Service，该类表示客户端要调用的远程服务，我们在AndroidManifest.xml文件中对该Service进行如下配置：我们通过android:process=:remote，让Service运行在一个新的进程中，而不是原有App的进程，其新进程的名字是remote，当然也可以是其他的名称。remote前面的冒号表示该进程被当前的App独享，是该App的私有进程；如果去掉remote前面的冒号，那么则表示该进程是被多个App所共享的。RemoteService源码如下所示：package com.ispring.aidldemo;import android.app.Service;import android.content.Intent;import android.os.*;import android.util.Log;import java.util.Random;public class RemoteService extends Service private Random random = new Random(); /callbacks存储了所有注册过的客户端回调 private final RemoteCallbackList callbacks = new RemoteCallbackList(); private static final int MSG_REPORT_DATA = 0; /该handler用来每隔一秒主动向所有注册过回调的客户端发送信息 private Handler handler = new Handler() Override public void handleMessage(Message msg) switch (msg.what) case MSG_REPORT_DATA: /开始广播，获取客户端的数量 final int n = callbacks.beginBroadcast(); int data = random.nextInt(100); for(int i = 0; i callback.dataChanged(data), PID= + android.os.Process.myPid() + , Thread= + Thread.currentThread().getName(); callback.dataChanged(data); catch (RemoteException e) e.printStackTrace(); /结束广播 callbacks.finishBroadcast(); /构建新的Message，延迟1秒发送，这样handler每隔一秒都会受到Message Message pendingMsg = obtainMessage(MSG_REPORT_DATA); sendMessageDelayed(pendingMsg, 1000); break; default: super.handleMessage(msg); ; /我们要实现 IRemoteInterface.Stub binder = new IRemoteInterface.Stub() Override public int getPid() throws RemoteException return android.os.Process.myPid(); Override public int getData() throws RemoteException Log.i(DemoLog, RemoteService: binder - getData, PID= + android.os.Process.myPid() + , Thread= + Thread.currentThread().getName(); return random.nextInt(100); Override public void registerCallback(IRemoteInterfaceCallback cb) throws RemoteException Log.i(DemoLog, RemoteService: binder - registerCallback, PID= + android.os.Process.myPid() + , Thread= + Thread.currentThread().getName(); if(cb != null) /注册客户端回调 callbacks.register(cb); Override public void unregisterCallback(IRemoteInterfaceCallback cb) throws RemoteException Log.i(DemoLog, RemoteService: binder - unregisterCallback, PID= + android.os.Process.myPid() + , Thread= + Thread.currentThread().getName(); if(cb != null) /反注册客户端回调 callbacks.unregister(cb); ; public RemoteService() Override public void onCreate() super.onCreate(); handler.sendEmptyMessage(MSG_REPORT_DATA); Log.i(DemoLog, RemoteService - onCreate, PID= + android.os.Process.myPid() + , Thread= + Thread.currentThread().getName(); Override public IBinder onBind(Intent intent) return binder; Override public void onDestroy() Log.i(DemoLog, RemoteService - onDestroy, PID= + android.os.Process.myPid() + , Thread= + Thread.currentThread().getName(); /反注册所有的客户端回调，并且不再接收新的客户端回调 callbacks.kill(); /移除pedding message，停止message循环，防止内存泄露 handler.removeMessages(MSG_REPORT_DATA); super.onDestroy(); 我们对上述部分代码进行说明：首先我们通过IRemoteInterface.Stub binder = new IRemoteInterface.Stub()实例化了一个IRemoteInterface.Stub对象。之前我们提到IRemoteInterface.Stub继承自android.os.Binder，所以该实例也就是一个Binder，并且其实现了接口IRemoteInterface定义的抽象方法。然后在Service的onBind接口中将上述binder对象返回，这样才能让客户端通过bindService方法调用Service。我们在后面会解释handler、客户端回调相关的代码片段。AIDL之客户端实现通常调用Service的客户端是Activity，我在MainActivity中调用RemoteService，其界面如下所示：客户端MainActivity源码如下所示：package com.ispring.aidldemo;import android.content.ComponentName;import android.content.Intent;import android.content.ServiceConnection;import android.os.*;import android.app.Activity;import android.util.Log;import android.view.View;import android.widget.Button;import android.widget.TextView;import android.widget.Toast;public class MainActivity extends Activity implements Button.OnClickListener private Button btnBindService; private Button btnGetData; private Button btnRegister; private Button btnUnregister; private Button btnUnbindService; private Button btnKillProcess; private TextView textView; private boolean isRegistered = false; private IRemoteInterface remoteInterface; private static final int MSG_GET_DATA = 0; private static final int MSG_DATA_CHANGED = 1; /handler用于在主线程中更新UI private Handler handler = new Handler() Override public void handleMessage(Message msg) switch (msg.what) case MSG_GET_DATA: /通过远程服务的getData方法获取数据 Toast.makeText(MainActivity.this, Data: + msg.arg1, Toast.LENGTH_LONG).show(); break; case MSG_DATA_CHANGED: /远程服务通过客户端回调向客户端推送数据 textView.setText(Receive data from service: + msg.arg1); break; default: super.handleMessage(msg); ; private ServiceConnection sc = new ServiceConnection() Override public void onServiceConnected(ComponentName name, IBinder binder) Log.i(DemoLog, MainActivity: ServiceConnection - onServiceConnected); remoteInterface = IRemoteInterface.Stub.asInterface(binder); /更新UI状态 btnBindService.setEnabled(false); btnGetData.setEnabled(true); btnRegister.setEnabled(true); btnUnregister.setEnabled(false); btnUnbindService.setEnabled(true); btnKillProcess.setEnabled(true); textView.setText(已连接到RemoteService); Override public void onServiceDisconnected(ComponentName name) Log.i(DemoLog, MainActivity: ServiceConnection - onServiceDisconnected); remoteInterface = null; /更新UI状态 btnBindService.setEnabled(true); btnGetData.setEnabled(false); btnRegister.setEnabled(false); btnUnregister.setEnabled(f