Android使用binder访问service的方式

1. 我们先来看一个与本地service通信的例子。

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。

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>  

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。

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.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。