Android菜鸟的成长笔记（21）——跨进程调用Service

我们都知道在Android中的每一个应用是一个进程，其实每一个应用就相当于Linux系统里面的一个用户，进程和进程之间的通信其实就相当于用户和用户之间的通信，为了实现这种跨进程通信，Android提供了AIDL Service (Android Interface definition language).

与邦等本地Service不同的是，本地Service的onBind()方法会直接把IBinder对象本身传给客户端的ServiceConnection的onServiceConnected方法的第二个参数。但远程Service的onBind()方法只是将IBinder对象的代理传给客户端的ServiceConnection的onService Connected方法的第二个参数。

ALDL定义的特点：

1、AIDL定义接口的源码必须以.aidl结尾。

2、AIDL接口中用到数据类型，除了基本类型、String、List、Map、CharSequence之外，其他类型全部都需要导包，即使它们在同一个包中也需要导包。

下面来具体实现一个示例：

（1）定义AIDL接口(和Java接口非常类似)

package com.example.testservice;interface ICat {String getColor();double getWeight();}

（2）定以好上面接口后保存，ADT工具会自动在gen.com.example.service目录下生成一个ICat.jar接口，在该接口中包含一个Stub内部类，该内部类实现了IBinder、ICat两个接口，这个Stub类将会作为远程Service的回调类——它实现了IBuilder接口，因此可作为Service的onBind()方法的返回值。这个Stub类就是一个代理类，同样可以实现IBinder的功能，并且还额外实现了ICat远程访问的功能。

自动生成的ICat.java接口

/* * This file is auto-generated.  DO NOT MODIFY. * Original file: D:\\adt-bundle-windows-x86-20130729\\eclipse\\workspace\\TestService\\src\\com\\example\\testservice\\ICat.aidl */package com.example.testservice;public interface ICat extends android.os.IInterface {/** Local-side IPC implementation stub class. */public static abstract class Stub extends android.os.Binder implementscom.example.testservice.ICat {private static final java.lang.String DESCRIPTOR = "com.example.testservice.ICat";/** Construct the stub at attach it to the interface. */public Stub() {this.attachInterface(this, DESCRIPTOR);}/** * Cast an IBinder object into an com.example.testservice.ICat * interface, generating a proxy if needed. */public static com.example.testservice.ICat asInterface(android.os.IBinder obj) {if ((obj == null)) {return null;}android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);if (((iin != null) && (iin instanceof com.example.testservice.ICat))) {return ((com.example.testservice.ICat) iin);}return new com.example.testservice.ICat.Stub.Proxy(obj);}@Overridepublic android.os.IBinder asBinder() {return this;}@Overridepublic 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_getColor: {data.enforceInterface(DESCRIPTOR);java.lang.String _result = this.getColor();reply.writeNoException();reply.writeString(_result);return true;}case TRANSACTION_getWeight: {data.enforceInterface(DESCRIPTOR);double _result = this.getWeight();reply.writeNoException();reply.writeDouble(_result);return true;}}return super.onTransact(code, data, reply, flags);}private static class Proxy implements com.example.testservice.ICat {private android.os.IBinder mRemote;Proxy(android.os.IBinder remote) {mRemote = remote;}@Overridepublic android.os.IBinder asBinder() {return mRemote;}public java.lang.String getInterfaceDescriptor() {return DESCRIPTOR;}@Overridepublic java.lang.String getColor()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);mRemote.transact(Stub.TRANSACTION_getColor, _data, _reply,0);_reply.readException();_result = _reply.readString();} finally {_reply.recycle();_data.recycle();}return _result;}@Overridepublic double getWeight() throws android.os.RemoteException {android.os.Parcel _data = android.os.Parcel.obtain();android.os.Parcel _reply = android.os.Parcel.obtain();double _result;try {_data.writeInterfaceToken(DESCRIPTOR);mRemote.transact(Stub.TRANSACTION_getWeight, _data, _reply,0);_reply.readException();_result = _reply.readDouble();} finally {_reply.recycle();_data.recycle();}return _result;}}static final int TRANSACTION_getColor = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);static final int TRANSACTION_getWeight = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);}public java.lang.String getColor() throws android.os.RemoteException;public double getWeight() throws android.os.RemoteException;}

（3）定义一个Service实现类，该Service的onBind()方法所返回的IBinder对象应该是ADT所生成的ICat.Stub的子类的实例。这一步的主要作用是将上面创建的接口暴漏给客户端。

package com.example.testservice;import java.util.Timer;import java.util.TimerTask;import com.example.testservice.ICat.Stub;import android.app.Service;import android.content.Intent;import android.os.IBinder;import android.os.RemoteException;public class AidlService extends Service{private CatBinder catBinder;Timer timer = new Timer();String[] colors = new String[]{"红色","黄色","黑色"};double[] weights = new double[]{2.3,3.1,1.58};private String color;private double weight;@Overridepublic IBinder onBind(Intent intent) {/* * 返回catBinder对象 * 在绑定本地Service的情况下，该catBinder对象会直接传给客户端的 * ServiceConnection对象的onServiceConnected方法的第二个参数； * 在绑定远程Service的情况下，只将catBinder对象的代理传给客户端的 * ServiceConnection对象的onServiceConnected方法的第二个参数； */return catBinder;}//继承Stub，也就是实现了ICat接口，并实现了IBinder接口public class CatBinder extends Stub{@Overridepublic String getColor() throws RemoteException {// TODO Auto-generated method stubreturn color;}@Overridepublic double getWeight() throws RemoteException {// TODO Auto-generated method stubreturn weight;}}@Overridepublic void onCreate() {super.onCreate();catBinder = new CatBinder();timer.schedule(new TimerTask() {@Overridepublic void run() {int rand = (int)(Math.random() * 3);color = colors[rand];weight = weights[rand];System.out.println("---------" + rand);}}, 0, 800);}}

（4）在AndroidMainfest.xml文件中配置该Service

        <service android:name=".AidlService">            <intent-filter>                <action android:name="com.example.testservice.action.AIDL_SERVICE"/>            </intent-filter>        </service>

（5）客户端访问AIDL Service

上面说过AIDL是定义在两个进程之间通信的一个接口，既然是一个通信协议，客户端同样需要前面定义的AIDL接口，所以第一步就是将AIDL文件复制到客户端应用中。

package com.example.testservice;import android.app.Activity;import android.app.Service;import android.content.ComponentName;import android.content.Intent;import android.content.ServiceConnection;import android.os.IBinder;import android.os.RemoteException;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;public class AidlClient extends Activity{private ICat catService;private Button get;EditText color, weight;private ServiceConnection conn = new ServiceConnection() {@Overridepublic void onServiceDisconnected(ComponentName name) {}@Overridepublic void onServiceConnected(ComponentName name, IBinder service) {//获取远程Service的onBind方法返回的对象的代理catService = ICat.Stub.asInterface(service);}};protected void onCreate(android.os.Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);get = (Button)findViewById(R.id.get);color = (EditText)findViewById(R.id.color);weight = (EditText)findViewById(R.id.weight);//创建所需绑定的Service的IntentIntent intent = new Intent();intent.setAction("com.example.testservice.action.AIDL_SERVICE");bindService(intent, conn, Service.BIND_AUTO_CREATE);get.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View arg0) {try {color.setText(catService.getColor());weight.setText(catService.getWeight() + "");} catch (RemoteException e) {e.printStackTrace();}}});};@Overrideprotected void onDestroy() {super.onDestroy();//解除绑定this.unbindService(conn);}}

下一篇将介绍如何在进程之间传递复杂数据

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