使用AIDL实现进程通信

使用AIDL和远程服务实现进程通信

    在Android中，每个应用程序都有自己的进程，当需要在不同的进程之间传递对象时，该如何实现呢？显然，java中是不支持垮进程内存共享的。因此要传递对象，需要把对象解析成操作系统能够理解的数据格式，以达到垮界对象访问的目的。在java ee中，采用RMI通过序列化传递对象。在android中，采用AIDL(Android Interface Definition Language:j接口定义语言）方式实现。

    AIDL是一种接口定义语言，用于约束两个进程间的通讯规则，供编译器生成代码，实现Android设备上的两个进程间通信（IPC)。AIDL的IPC机制和EJB所采用的CORBA很类似，进程之间的通信信息，首先会被转换成AIDL协议信息，然后发送给对方，对方收到AIDL协议消息后再转换成相应的对象。由于进程之间的通信信息需要双向转换，所以android采用代理类在背后实现了信息的双向转换，代理类由android编译器生成，对开发人员来说是透明的。

一、服务端的实现：

1、写一个AIDL文件：

package cn.license.android;interface StudentRemote {String QueryStudent(int studentNo);}

2、开发工具自动生成一个接口：

/* * This file is auto-generated.  DO NOT MODIFY. * Original file: C:\\Users\\Administrator\\workspace\\StudentRemoteService\\src\\cn\\license\\android\\StudentRemote.aidl */package cn.license.android;public interface StudentRemote extends android.os.IInterface{/** Local-side IPC implementation stub class. */public static abstract class Stub extends android.os.Binder implements cn.license.android.StudentRemote{private static final java.lang.String DESCRIPTOR = "cn.license.android.StudentRemote";/** Construct the stub at attach it to the interface. */public Stub(){this.attachInterface(this, DESCRIPTOR);}/** * Cast an IBinder object into an cn.license.android.StudentRemote interface, * generating a proxy if needed. */public static cn.license.android.StudentRemote asInterface(android.os.IBinder obj){if ((obj==null)) {return null;}android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);if (((iin!=null)&&(iin instanceof cn.license.android.StudentRemote))) {return ((cn.license.android.StudentRemote)iin);}return new cn.license.android.StudentRemote.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_QueryStudent:{data.enforceInterface(DESCRIPTOR);int _arg0;_arg0 = data.readInt();java.lang.String _result = this.QueryStudent(_arg0);reply.writeNoException();reply.writeString(_result);return true;}}return super.onTransact(code, data, reply, flags);}private static class Proxy implements cn.license.android.StudentRemote{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 java.lang.String QueryStudent(int studentNo) throws android.os.RemoteException{android.os.Parcel _data = android.os.Parcel.obtain();android.os.Parcel _reply = android.os.Parcel.obtain();java.lang.String _result;try {_data.writeInterfaceToken(DESCRIPTOR);_data.writeInt(studentNo);mRemote.transact(Stub.TRANSACTION_QueryStudent, _data, _reply, 0);_reply.readException();_result = _reply.readString();}finally {_reply.recycle();_data.recycle();}return _result;}}static final int TRANSACTION_QueryStudent = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);}public java.lang.String QueryStudent(int studentNo) throws android.os.RemoteException;}

3、service的代码：

public class StudentRemoteService extends Service {private String[] students={"name1","name 2","name 3"};private IBinder binder = new StudentRemoteBinder();@Overridepublic IBinder onBind(Intent intent) {return binder;}private String QueryStudentName(int studentNo){if(studentNo>0 && studentNo<=students.length){return students[studentNo-1];}return null;}

//继承开发工具自动生成的接口里面的一个类private final class StudentRemoteBinder extends StudentRemote.Stub{@Overridepublic String QueryStudent(int studentNo) throws RemoteException {return QueryStudentName(studentNo);}}}

4、配置service的action:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="cn.license.android"    android:versionCode="1"    android:versionName="1.0" >    <uses-sdk        android:minSdkVersion="8"        android:targetSdkVersion="17" />    <application        android:allowBackup="true"        android:icon="@drawable/ic_launcher"        android:label="@string/app_name"        android:theme="@style/AppTheme" >        <service android:name=".StudentRemoteService">            <intent-filter>                <action android:name="cn.license.studentQuery"/>            </intent-filter>        </service>    </application></manifest>

这里遇到一个问题，笔者写错了manifest  的 package，然后安装到设备上，后来改正确路劲了，还是报这个错误：java lang runtimeexception unable to instantiate service。直至在设备上删除这个服务，再安装它，重新启动设备，这个错误才消失。

二、客户端的实现

1、把服务端的aidl 文件（包括路劲）复制到 客户端；

2、客户端的代码实现：

public class MainActivity extends Activity {private ServiceConnection conn = new StudentServiceConnection();//private IStudentBinder studentService;private StudentRemote studentRemote;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//显示意图//Intent service = new Intent(this,StudentService.class);//隐式意图，此处用来激活远程服务Intent service = new Intent("cn.license.studentQuery");bindService(service, conn, BIND_AUTO_CREATE);}@Overrideprotected void onDestroy() {super.onDestroy();unbindService(conn);}public void query(View v){EditText studentNoText = (EditText)this.findViewById(R.id.studentNo);int studentNo = Integer.valueOf(studentNoText.getText().toString());String studentName="";try {studentName = studentRemote.QueryStudent(studentNo);} catch (RemoteException e) {// TODO Auto-generated catch blocke.printStackTrace();}//studentService.QueryName(studentNo);TextView studentNameText = (TextView) this.findViewById(R.id.studentName);studentNameText.setText(studentName);}private class StudentServiceConnection implements ServiceConnection{@Overridepublic void onServiceConnected(ComponentName name, IBinder service) {//本地//studentService = (IStudentBinder)service;//远程 aidlstudentRemote = StudentRemote.Stub.asInterface(service);}@Overridepublic void onServiceDisconnected(ComponentName name) {//studentService=null;studentRemote = null;}}}