Android 使用binder访问service的方式

binder机制是贯穿整个Android系统的进程间访问机制，经常被用来访问service，我们结合代码看一下binder在访问service的情形下是怎么具体使用的。

service 你可以理解成没有的界面的activity，它是跑在后台的程序，所谓后台是相对于可以被看得到的程序的，后台程序是不能直接交互的程序。

binder主要是用来进程间通信的，但也可用在和本地service通信。

1. 我们先来看一个与本地service通信的例子。

package com.ckt.wangxin;

import android.app.Service;

import android.content.Intent;

import android.os.Binder;

import android.os.IBinder;

import android.widget.Toast;

/**

 * This is a service stub for both LocalBinderClient

 * and RemoteBinderClient

 * @author Wang Xin

 * @email springnap@163.com

 *

 */

public class LocalService extends Service {

    @Override

    public IBinder onBind(Intent intent) {

        return new LocalBinder();

    }   

    public void sayHelloWorld(){

        Toast.makeText(this.getApplicationContext(), "Hello World Local Service!", Toast.LENGTH_SHORT).show();

    }   

    public class LocalBinder extends Binder {

        LocalService getService() {

            // Return this instance of LocalService so clients can call public methods

            return LocalService.this;

        }

    }

}

local servcie 的代码如上，在onBinder方法中返回binder，binder包含了service的句柄，客户端得到句柄以后就可以调用servcie的公共方法了，这种调用方式是最常见的。

客户端代码

package com.ckt.wangxin;

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.util.Log;

import com.ckt.wangxin.LocalService.LocalBinder;

public class LocalServiceTestActivity extends Activity {

    static final String TAG = "LocalBinderTestActivity";

    ServiceConnection mSc;

    /** Called when the activity is first created. */

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        mSc = new ServiceConnection(){

            @Override

            public void onServiceConnected(ComponentName name, IBinder service) {

                Log.d(TAG, "service connected");

                LocalService ss = ((LocalBinder)service).getService();

                ss.sayHelloWorld();

            }

            @Override

            public void onServiceDisconnected(ComponentName name) {

                Log.d(TAG, "service disconnected");

            }

        };

    }

    @Override

    protected void onStart() {

        super.onStart();

        Log.d(TAG, this.getApplicationContext().getPackageCodePath());

        Intent service = new Intent(this.getApplicationContext(),LocalService.class);

        this.bindService(service, mSc, Context.BIND_AUTO_CREATE);

    }

    @Override

    protected void onStop() {

        super.onStop();

        //must unbind the service otherwise the ServiceConnection will be leaked.

        <span style="color: rgb(255, 0, 0); ">this.unbindService(mSc);</span>

    }

}

需要注意的是在onStop中要解绑定service, 否则会造成内存泄露的问题。

2. 我们再看一下与另外一个进程中的service进行通信的问题（跨进程通信！）。

如何将servcie运行在另外一个进程呢？在manifest 里面配置个属性就行了。

android:process=":remote" , 代表这个service运行在同一个应用程序的不同进程中。

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.ckt.wangxin"

    android:versionCode=""

    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="" />

    <application

        android:icon="@drawable/ic_launcher"

        android:label="@string/app_name" >

        <activity

            android:name=".LocalServiceTestActivity"

            android:label="@string/app_name" >

           <!--  <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter> -->

        </activity>

        <service android:name=".LocalService"></service>

        <!-- android:process=":remote" specify this service run in

        another process in the same application. -->

        <service android:name=".RemoteService" android:process=":remote"></service>

        <activity android:name="RemoteServiceTestActivity">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

    </application>

</manifest>

客户端可以使用Messenger发送消息到service。

客户端代码：

package com.ckt.wangxin;

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.Handler;

import android.os.IBinder;

import android.os.Message;

import android.os.Messenger;

import android.os.RemoteException;

import android.util.Log;

import android.widget.Toast;

public class RemoteServiceTestActivity extends Activity {

    static final String TAG = "RemoteServiceTestActivity";

    ServiceConnection mSc;

    public static final int SAY_HELLO_TO_CLIENT = ;

    /**

     * Handler of incoming messages from service.

     */

    class IncomingHandler extends Handler {

        @Override

        public void handleMessage(Message msg) {

            switch (msg.what) {

                case SAY_HELLO_TO_CLIENT:

                    Toast.makeText(RemoteServiceTestActivity.this.getApplicationContext(), "Hello World Remote Client!",

                            Toast.LENGTH_SHORT).show();

                    break;

                default:

                    super.handleMessage(msg);

            }

        }

    }

    Messenger messenger_reciever = new Messenger(new IncomingHandler());

    /** Called when the activity is first created. */

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        mSc = new ServiceConnection(){

            @Override

            public void onServiceConnected(ComponentName name, IBinder service) {

                Log.d(TAG, "service connected");

                <span style="color: rgb(204, 0, 0); ">Messenger messenger = new Messenger(service);

                Message msg = new Message();

                msg.what = RemoteService.MSG_SAY_HELLO;</span>

                msg.replyTo = messenger_reciever;

                try {

                    <span style="color: rgb(255, 0, 0); ">messenger.send(msg);</span>

                } catch (RemoteException e) {

                    e.printStackTrace();

                }

            }

            @Override

            public void onServiceDisconnected(ComponentName name) {

                Log.d(TAG, "service disconnected");

            }

        };

    }

    @Override

    protected void onStart() {

        super.onStart();

        Log.d(TAG, this.getApplicationContext().getPackageCodePath());

        Intent service = new Intent(this.getApplicationContext(),RemoteService.class);

        this.bindService(service, mSc, Context.BIND_AUTO_CREATE);

    }

    @Override

    protected void onStop() {

        super.onStop();

        //must unbind the service otherwise the ServiceConnection will be leaked.

        this.unbindService(mSc);

    }

}

获得service端传来的binder，用来构建一个Messenger向service发送消息。

service端代码：

package com.ckt.wangxin;

import android.app.Service;

import android.content.Intent;

import android.os.Handler;

import android.os.IBinder;

import android.os.Message;

import android.os.Messenger;

import android.os.RemoteException;

import android.widget.Toast;

public class RemoteService extends Service {

    public static final int MSG_SAY_HELLO = ;

    @Override

    public IBinder onBind(Intent intent) {

      <span style="color: rgb(204, 0, 0); ">  return messager.getBinder();</span>

    }

    Handler IncomingHandler = new Handler() {

        @Override

        public void handleMessage(Message msg) {

            if(msg.replyTo != null){

                Message msg_client = this.obtainMessage();

                msg_client.what = RemoteServiceTestActivity.SAY_HELLO_TO_CLIENT;

                try {

                    ((Messenger)msg.replyTo).send(msg_client);

                } catch (RemoteException e) {

                    // TODO Auto-generated catch block

                    e.printStackTrace();

                }

            }

            switch (msg.what) {

                case MSG_SAY_HELLO:

                    Toast.makeText(RemoteService.this.getApplicationContext(), "Hello World Remote Service!",

                            Toast.LENGTH_SHORT).show();

                    break;

                default:

            super.handleMessage(msg);

            }

        }

    };

    Messenger  messager = new Messenger (IncomingHandler);

}

构建一个Messenger，包含一个handler，然后将messenger的binder传给客户端，客户端可以通过handler再构造一个messenger与service通信，消息在handler里面被处理。

现在是service端单向响应客户端的消息，同理可以做成双向发送消息，实现双向通信。

demo 源码可以在这里下载源代码下载

巴特西

Android 使用binder访问service的方式

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