Android 使用binder访问service的方式

Posted 2020-08-17 星辰

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 [email protected]
 *
 */
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="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");
                <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) {
      <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