Android Activity与Service通信（不同进程之间）详解

 public class LocalService extends Service { 
  // 实例化自定义的Binder类 
  private final IBinder mBinder = new LocalBinder(); 
  // 随机数的生成器 
  private final Random mGenerator = new Random(); 
 
  /** 
   * 自定义的Binder类，这个是一个内部类，所以可以知道其外围类的对象，通过这个类，让Activity知道其Service的对象 
   */ 
  public class LocalBinder extends Binder { 
    LocalService getService() { 
      // 返回Activity所关联的Service对象，这样在Activity里，就可调用Service里的一些公用方法和公用属性 
      return LocalService.this; 
    } 
  } 
 
  @Override 
  public IBinder onBind(Intent intent) { 
    return mBinder; 
  } 
 
  /** public方法，Activity可以进行调用 */ 
  public int getRandomNumber() { 
   return mGenerator.nextInt(100); 
  } 
} 
 

public class BindingActivity extends Activity { 
  LocalService mService; 
  boolean mBound = false; 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
  } 
 
  @Override 
  protected void onStart() { 
    super.onStart(); 
    // 绑定Service，绑定后就会调用mConnetion里的onServiceConnected方法 
    Intent intent = new Intent(this, LocalService.class); 
    bindService(intent, mConnection, Context.BIND_AUTO_CREATE); 
  } 
 
  @Override 
  protected void onStop() { 
    super.onStop(); 
    // 解绑Service，这样可以节约内存 
    if (mBound) { 
      unbindService(mConnection); 
      mBound = false; 
    } 
  } 
 
  /** 用户点击button，就读取Service里的随机数 */ 
  public void onButtonClick(View v) { 
    if (mBound) { 
      // 用Service的对象，去读取随机数 
      int num = mService.getRandomNumber(); 
      Toast.makeText(this, "number: " + num, Toast.LENGTH_SHORT).show(); 
    } 
  } 
 
  /** 定交ServiceConnection，用于绑定Service的*/ 
  private ServiceConnection mConnection = new ServiceConnection() { 
 
    @Override 
    public void onServiceConnected(ComponentName className, 
        IBinder service) { 
      // 已经绑定了LocalService，强转IBinder对象，调用方法得到LocalService对象 
      LocalBinder binder = (LocalBinder) service; 
      mService = binder.getService(); 
      mBound = true; 
    } 
 
    @Override 
    public void onServiceDisconnected(ComponentName arg0) { 
      mBound = false; 
    } 
  }; 
} 

 public class MessengerService extends Service { 
  /** 用于Handler里的消息类型 */ 
  static final int MSG_SAY_HELLO = 1; 
 
  /** 
   * 在Service处理Activity传过来消息的Handler 
   */ 
  class IncomingHandler extends Handler { 
    @Override 
    public void handleMessage(Message msg) { 
      switch (msg.what) { 
        case MSG_SAY_HELLO: 
          Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show(); 
          break; 
        default: 
          super.handleMessage(msg); 
      } 
    } 
  } 
 
  /** 
   * 这个Messenger可以关联到Service里的Handler，Activity用这个对象发送Message给Service，Service通过Handler进行处理。 
   */ 
  final Messenger mMessenger = new Messenger(new IncomingHandler()); 
 
  /** 
   * 当Activity绑定Service的时候，通过这个方法返回一个IBinder，Activity用这个IBinder创建出的Messenger，就可以与Service的Handler进行通信了 
   */ 
  @Override 
  public IBinder onBind(Intent intent) { 
    Toast.makeText(getApplicationContext(), "binding", Toast.LENGTH_SHORT).show(); 
    return mMessenger.getBinder(); 
  } 
} 
 

public class ActivityMessenger extends Activity { 
  /** 向Service发送Message的Messenger对象 */ 
  Messenger mService = null; 
 
  /** 判断有没有绑定Service */ 
  boolean mBound; 
 
  private ServiceConnection mConnection = new ServiceConnection() { 
    public void onServiceConnected(ComponentName className, IBinder service) { 
      // Activity已经绑定了Service 
      // 通过参数service来创建Messenger对象，这个对象可以向Service发送Message，与Service进行通信 
      mService = new Messenger(service); 
      mBound = true; 
    } 
 
    public void onServiceDisconnected(ComponentName className) { 
      mService = null; 
      mBound = false; 
    } 
  }; 
 
  public void sayHello(View v) { 
    if (!mBound) return; 
    // 向Service发送一个Message 
    Message msg = Message.obtain(null, MessengerService.MSG_SAY_HELLO, 0, 0); 
    try { 
      mService.send(msg); 
    } catch (RemoteException e) { 
      e.printStackTrace(); 
    } 
  } 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
  } 
 
  @Override 
  protected void onStart() { 
    super.onStart(); 
    // 绑定Service 
    bindService(new Intent(this, MessengerService.class), mConnection, 
      Context.BIND_AUTO_CREATE); 
  } 
 
  @Override 
  protected void onStop() { 
    super.onStop(); 
    // 解绑 
    if (mBound) { 
      unbindService(mConnection); 
      mBound = false; 
    } 
  } 
}