Android中AIDL使用例子

本文提供了一个关于AIDL使用的简单易懂的例子，分为客户端和服务端两部分，分别为客户端和服务端新建一个eclipse工程，实现了从客户端向服务端发送请求，服务端打印log的功能。

客户端和服务端的源码结构如下：

注意，由于客户端和服务端的aidl文件所在包名必须一样，而两个包名一样的程序在安装时会产生冲突，所以这里用了一个技巧，在客户端工程的AndroidManifest.xml里把包名指定为com.styleflying，所以大家就会看到gen目录下的R.java所在的包是com.styleflying而不是com.styleflying.AIDL

正文

现在客户端和服务端工程分别新建一个aidl接口，所在包和文件名必须一样。两个aidl接口是一样的，内容如下：

<textarea cols="49" rows="7" name="code" class="java">package com.styleflying.AIDL; interface mInterface{ void invokTest(); }</textarea>

自动编译生成.java文件如下：

<textarea cols="48" rows="10" name="code" class="java">/* * This file is auto-generated. DO NOT MODIFY. * Original file: G://workspace//AidlDemo_client//src//com//styleflying//AIDL//mInterface.aidl */ package com.styleflying.AIDL; public interface mInterface extends android.os.IInterface { /** Local-side IPC implementation stub class. */ public static abstract class Stub extends android.os.Binder implements com.styleflying.AIDL.mInterface { private static final java.lang.String DESCRIPTOR = "com.styleflying.AIDL.mInterface"; /** C**truct the stub at attach it to the interface. */ public Stub() { this.attachInterface(this, DESCRIPTOR); } /** * Cast an IBinder object into an com.styleflying.AIDL.mInterface interface, * generating a proxy if needed. */ public static com.styleflying.AIDL.mInterface asInterface(android.os.IBinder obj) { if ((obj==null)) { return null; } android.os.IInterface iin = (android.os.IInterface)obj.queryLocalInterface(DESCRIPTOR); if (((iin!=null)&&(iin instanceof com.styleflying.AIDL.mInterface))) { return ((com.styleflying.AIDL.mInterface)iin); } return new com.styleflying.AIDL.mInterface.Stub.Proxy(obj); } 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_invokTest: { data.enforceInterface(DESCRIPTOR); this.invokTest(); reply.writeNoException(); return true; } } return super.onTransact(code, data, reply, flags); } private static class Proxy implements com.styleflying.AIDL.mInterface { private android.os.IBinder mRemote; Proxy(android.os.IBinder remote) { mRemote = remote; } public android.os.IBinder asBinder() { return mRemote; } public java.lang.String getInterfaceDescriptor() { return DESCRIPTOR; } public void invokTest() throws android.os.RemoteException { android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); try { _data.writeInterfaceToken(DESCRIPTOR); mRemote.transact(Stub.TRANSACTION_invokTest, _data, _reply, 0); _reply.readException(); } finally { _reply.recycle(); _data.recycle(); } } } static final int TRANSACTION_invokTest = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0); } public void invokTest() throws android.os.RemoteException; } </textarea>

客户端的mAIDLActivity.java如下：

<textarea cols="50" rows="15" name="code" class="java">package com.styleflying.AIDL; import android.app.Activity; import android.content.ComponentName; import android.content.Context; import android.content.Intent; import android.content.ServiceConnection; import android.os.Bundle; import android.os.IBinder; import android.os.RemoteException; import android.util.Log; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.Toast; import com.styleflying.R; public class mAIDLActivity extends Activity { private static final String TAG = "AIDLActivity"; private Button btnOk; private Button btnCancel; private Button btnCallBack; private void Log(String str){ Log.d(TAG,"----------" + str + "----------"); } mInterface mService; private ServiceConnection mConnection = new ServiceConnection(){ public void **erviceConnected(ComponentName className, IBinder service){ Log("connect service"); mService = mInterface.Stub.asInterface(service); } public void **erviceDisconnected(ComponentName className){ Log("disconnect service"); mService = null; } }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); btnOk = (Button)findViewById(R.id.btn_ok); btnCancel = (Button)findViewById(R.id.btn_cancel); btnCallBack = (Button)findViewById(R.id.btn_callback); btnOk.setOnClickListener(new OnClickListener(){ public void onClick(View v){ Bundle args = new Bundle(); Intent intent = new Intent("com.styleflying.AIDL.service"); intent.putExtras(args); bindService(intent,mConnection,Context.BIND_AUTO_CREATE); } }); btnCancel.setOnClickListener(new OnClickListener(){ public void onClick(View v){ unbindService(mConnection); } }); btnCallBack.setOnClickListener(new OnClickListener(){ public void onClick(View v){ try{ Log.i(TAG,"current Thread id = " + Thread.currentThread().getId()); mService.invokTest(); } catch(RemoteException e){ } } }); } }</textarea>

客户端在执行bindService的时候，成功绑定服务之后，会回调mConnection的**erviceConnected(),并且传回了服务端的通信接口IBinder，此IBinder即服务onBind()时返回的IBinder，详见mAIDLService.java。

在**erviceConnected(),客户端成功获取了服务端通信接口，实际上是本地代理对象，该对象存在于客户端进程空间，客户端只和代理对象交互，真正的IPC通信是本地代理对象和服务端的通信。

mAIDLService.java如下：

<textarea cols="50" rows="15" name="code" class="c-sharp">package com.styleflying.AIDL; import android.app.Service; import android.content.Intent; import android.os.IBinder; import android.os.Looper; import android.os.RemoteException; import android.util.Log; import android.widget.Toast; public class mAIDLService extends Service{ private static final String TAG = "AIDLService"; private void Log(String str){ Log.i(TAG,"----------" + str + "----------"); } public void onCreate(){ Log("service created"); } public void **tart(Intent intent, int startId){ Log("service started id = " + startId); } public IBinder onBind(Intent t){ Log("service on bind"); return mBinder; } public void onDestroy(){ Log("service on destroy"); super.onDestroy(); } public boolean onUnbind(Intent intent){ Log("service on unbind"); return super.onUnbind(intent); } public void onRebind(Intent intent){ Log("service on rebind"); super.onRebind(intent); } private final mInterface.Stub mBinder = new mInterface.Stub() {        public void invokTest() throws RemoteException { // TODO Auto-generated method stub Log.e(TAG, "remote call from client! current thread id = " + Thread.currentThread().getId()); } }; } </textarea>

注意onBind()函数，返回了mBinder，而mBinder实现了mInterface.Stub，实现了mInterface接口，执行了打印log的操作。

整个交互流程如下：

1.客户端通过绑定服务，获取了服务的句柄(本地代理对象)；

2.客户端执行onClick()，调用本地代理对象的invokTest()函数，本地代理对象调用mRemote.transact()发出远程调用请求（见   mInterface.java）；

3.服务端响应onTransact()执行this.invokTest()，并将执行结果返回；

由于客户端只和本地代理对象即服务句柄通信，由代理对象进行真正的IPC操作，所以对客户端来说，IPC过程是透明的，调用远程操作如同调用本地操作一样。在客户端调用transact()时，会将服务描述DSCRIPTION写入到data里，在客户端onTransact时会验证，如果两个不一样，则不能通信。而DSCRIPTION是根据mInterface包名和接口名自动生成的，这就是为什么两个工程里的mInterface.aidl要在同一个包的原因。

在这个过程中，mInterface.aidl起到了桥梁的作用，规定统一了客户端和服务端的通信接口，使得客户端和服务端得以成功的通信。

具体的通信transact和onTransact的过程也就是利用Binder驱动通信的过程，在这里就不多叙述。

最后补上两个工程的AndroidManifest.xml

<textarea cols="50" rows="15" name="code" class="xhtml"><?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.styleflying" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".AIDL.mAIDLActivity" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion="8" /> </manifest> </textarea><textarea cols="50" rows="15" name="code" class="xhtml"><?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.styleflying.AIDL" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <service android:name=".mAIDLService"> <intent-filter> <action android:name="com.styleflying.AIDL.service" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter> </service> </application> <uses-sdk android:minSdkVersion="8" /> </manifest> </textarea>