AIDL---使用AIDL实现进程间的通信 .

在Android中，如果我们需要在不同进程间实现通信，就需要用到AIDL技术去完成。

AIDL（Android Interface Definition Language）是一种接口定义语言，编译器通过*.aidl文件的描述信息生成符合通信协议的Java代码，我们无需自己去写这段繁杂的代码，只需要在需要的时候调用即可，通过这种方式我们就可以完成进程间的通信工作。关于AIDL的编写规则我在这里就不多介绍了，读者可以到网上查找一下相关资料。

接下来，我就演示一个操作AIDL的最基本的流程。

首先，我们需要建立一个服务端的工程，如图所以：





在IPerson.aidl中我们定义了一个“问候”的方法，代码如下：

[java]
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package com.scott.aidl;
interface IPerson {
String greet(String someone);
}

[java] 
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package com.scott.aidl;  
  
public interface IPerson extends android.os.IInterface {  
    /** Local-side IPC implementation stub class. */  
    public static abstract class Stub extends android.os.Binder implements com.scott.aidl.IPerson {  
          
        private static final java.lang.String DESCRIPTOR = "com.scott.aidl.IPerson";  
  
        /** Construct the stub at attach it to the interface. */  
        public Stub() {  
            this.attachInterface(this, DESCRIPTOR);  
        }  
  
        /** 
         * Cast an IBinder object into an com.scott.aidl.IPerson interface, 
         * generating a proxy if needed. 
         */  
        public static com.scott.aidl.IPerson 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.scott.aidl.IPerson))) {  
                return ((com.scott.aidl.IPerson) iin);  
            }  
            return new com.scott.aidl.IPerson.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_greet: {  
                data.enforceInterface(DESCRIPTOR);  
                java.lang.String _arg0;  
                _arg0 = data.readString();  
                java.lang.String _result = this.greet(_arg0);  
                reply.writeNoException();  
                reply.writeString(_result);  
                return true;  
            }  
            }  
            return super.onTransact(code, data, reply, flags);  
        }  
  
        private static class Proxy implements com.scott.aidl.IPerson {  
            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 java.lang.String greet(java.lang.String someone) 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.writeString(someone);  
                    mRemote.transact(Stub.TRANSACTION_greet, _data, _reply, 0);  
                    _reply.readException();  
                    _result = _reply.readString();  
                } finally {  
                    _reply.recycle();  
                    _data.recycle();  
                }  
                return _result;  
            }  
        }  
  
        static final int TRANSACTION_greet = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);  
    }  
  
    public java.lang.String greet(java.lang.String someone) throws android.os.RemoteException;  
}  

package com.scott.aidl;

public interface IPerson extends android.os.IInterface {
	/** Local-side IPC implementation stub class. */
	public static abstract class Stub extends android.os.Binder implements com.scott.aidl.IPerson {
		
		private static final java.lang.String DESCRIPTOR = "com.scott.aidl.IPerson";

		/** Construct the stub at attach it to the interface. */
		public Stub() {
			this.attachInterface(this, DESCRIPTOR);
		}

		/**
		 * Cast an IBinder object into an com.scott.aidl.IPerson interface,
		 * generating a proxy if needed.
		 */
		public static com.scott.aidl.IPerson 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.scott.aidl.IPerson))) {
				return ((com.scott.aidl.IPerson) iin);
			}
			return new com.scott.aidl.IPerson.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_greet: {
				data.enforceInterface(DESCRIPTOR);
				java.lang.String _arg0;
				_arg0 = data.readString();
				java.lang.String _result = this.greet(_arg0);
				reply.writeNoException();
				reply.writeString(_result);
				return true;
			}
			}
			return super.onTransact(code, data, reply, flags);
		}

		private static class Proxy implements com.scott.aidl.IPerson {
			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 java.lang.String greet(java.lang.String someone) 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.writeString(someone);
					mRemote.transact(Stub.TRANSACTION_greet, _data, _reply, 0);
					_reply.readException();
					_result = _reply.readString();
				} finally {
					_reply.recycle();
					_data.recycle();
				}
				return _result;
			}
		}

		static final int TRANSACTION_greet = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
	}

	public java.lang.String greet(java.lang.String someone) throws android.os.RemoteException;
}

该文件的大纲视图如下：



IPerson接口中的抽象内部类Stub继承android.os.Binder类并实现IPerson接口，比较重要的方法是asInterface(IBinder)方法，该方法会将IBinder类型的对象转换成IPerson类型，必要的时候生成一个代理对象返回结果。

接下来就是我们的Service了：

[java]
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package com.scott.server;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.os.RemoteException;
import android.util.Log;

import com.scott.aidl.IPerson;

public class AIDLService extends Service {

private static final String TAG = "AIDLService";

IPerson.Stub stub = new IPerson.Stub() {
@Override
public String greet(String someone) throws RemoteException {
Log.i(TAG, "greet() called");
return "hello, " + someone;
}
};

@Override
public IBinder onBind(Intent intent) {
Log.i(TAG, "onBind() called");
return stub;
}

@Override
public boolean onUnbind(Intent intent) {
Log.i(TAG, "onUnbind() called");
return true;
}

@Override
public void onDestroy() {
super.onDestroy();
Log.i(TAG, "onDestroy() called");
}
}

[java] 
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<service android:name=".AIDLService">  
    <intent-filter>  
        <action android:name="android.intent.action.AIDLService" />  
             <category android:name="android.intent.category.DEFAULT" />  
    </intent-filter>  
</service>  

<service android:name=".AIDLService">
	<intent-filter>
		<action android:name="android.intent.action.AIDLService" />
             <category android:name="android.intent.category.DEFAULT" />
	</intent-filter>
</service>

服务端已经完成了，接下来我们就该完成客户端的工作了。我已经建好了一个客户端工程，如图：



我们只需要把IPerson.aidl文件拷到相应的目录中即可，编译器同样会生成相对应的IPerson.java文件，这一部分和服务端没什么区别。这样一来，服务端和客户端就在通信协议上达到了统一。我们主要工作在MainActivity中完成。

MainActivity代码如下：

[java]
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package com.scott.client;

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.widget.Button;
import android.widget.Toast;

import com.scott.aidl.IPerson;

public class MainActivity extends Activity {

private Button bindBtn;
private Button greetBtn;
private Button unbindBtn;

private IPerson person;
private ServiceConnection conn = new ServiceConnection() {

@Override
public void onServiceConnected(ComponentName name, IBinder service) {
Log.i("ServiceConnection", "onServiceConnected() called");
person = IPerson.Stub.asInterface(service);
}

@Override
public void onServiceDisconnected(ComponentName name) {
//This is called when the connection with the service has been unexpectedly disconnected,
//that is, its process crashed. Because it is running in our same process, we should never see this happen.
Log.i("ServiceConnection", "onServiceDisconnected() called");
}
};

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

bindBtn = (Button) findViewById(R.id.bindBtn);
bindBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent("android.intent.action.AIDLService");
bindService(intent, conn, Context.BIND_AUTO_CREATE);

bindBtn.setEnabled(false);
greetBtn.setEnabled(true);
unbindBtn.setEnabled(true);
}
});

greetBtn = (Button) findViewById(R.id.greetBtn);
greetBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
try {
String retVal = person.greet("scott");
Toast.makeText(MainActivity.this, retVal, Toast.LENGTH_SHORT).show();
} catch (RemoteException e) {
Toast.makeText(MainActivity.this, "error", Toast.LENGTH_SHORT).show();
}
}
});

unbindBtn = (Button) findViewById(R.id.unbindBtn);
unbindBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
unbindService(conn);

bindBtn.setEnabled(true);
greetBtn.setEnabled(false);
unbindBtn.setEnabled(false);
}
});
}
}

package com.scott.client;

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.widget.Button;
import android.widget.Toast;

import com.scott.aidl.IPerson;

public class MainActivity extends Activity {

private Button bindBtn;
private Button greetBtn;
private Button unbindBtn;

private IPerson person;
private ServiceConnection conn = new ServiceConnection() {

@Override
public void onServiceConnected(ComponentName name, IBinder service) {
Log.i("ServiceConnection", "onServiceConnected() called");
person = IPerson.Stub.asInterface(service);
}

@Override
public void onServiceDisconnected(ComponentName name) {
//This is called when the connection with the service has been unexpectedly disconnected,
//that is, its process crashed. Because it is running in our same process, we should never see this happen.
Log.i("ServiceConnection", "onServiceDisconnected() called");
}
};

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

bindBtn = (Button) findViewById(R.id.bindBtn);
bindBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent("android.intent.action.AIDLService");
bindService(intent, conn, Context.BIND_AUTO_CREATE);

bindBtn.setEnabled(false);
greetBtn.setEnabled(true);
unbindBtn.setEnabled(true);
}
});

greetBtn = (Button) findViewById(R.id.greetBtn);
greetBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
try {
String retVal = person.greet("scott");
Toast.makeText(MainActivity.this, retVal, Toast.LENGTH_SHORT).show();
} catch (RemoteException e) {
Toast.makeText(MainActivity.this, "error", Toast.LENGTH_SHORT).show();
}
}
});

unbindBtn = (Button) findViewById(R.id.unbindBtn);
unbindBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
unbindService(conn);

bindBtn.setEnabled(true);
greetBtn.setEnabled(false);
unbindBtn.setEnabled(false);
}
});
}
}

从代码中可以看到，我们要重写ServiceConnection中的onServiceConnected方法将IBinder类型的对像转换成我们的IPerson类型。到现在我们就剩下最后一个步骤了，这个环节也是最为关键的，就是绑定我们需要的服务。我们通过服务端Service定义的“android.intent.action.AIDLService”这个标识符来绑定其服务，这样客户端和服务端就实现了通信的连接，我们就可以调用IPerson中的“问候”方法了。

最后，贴几张客户端演示过程图。














按照顺序分别是：初始界面；点击bindService后界面；点击greet后界面；点击unbindService后界面。

操作过程中的日志如下：