Android使用binder访问service的方式（一）

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;
}
}
}

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.
this.unbindService(mSc);
}
}

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="1"
android:versionName="1.0" >
<uses-sdk android:minSdkVersion="15" />
<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>

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

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

    package="com.ckt.wangxin"

    android:versionCode="1"

    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="15" />

    <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 = 0;
/**
* 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");
Messenger messenger = new Messenger(service);
Message msg = new Message();
msg.what = RemoteService.MSG_SAY_HELLO;
msg.replyTo = messenger_reciever;
try {
messenger.send(msg);
} 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);
}
}

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 = 0;

    /**

     * 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 = 0;
@Override
public IBinder onBind(Intent intent) {
return messager.getBinder();
}
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);
}

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 = 0;

    @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。

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