Acitivity与Service的交互方式

（一） Extending the Binder class

通过 Binder 接口的形式实现，当 Activity 绑定 Service 成功的时候 Activity 会在<code> ServiceConnection </code>类的 <code>onServiceConnected()</code>回调方法中获取到 Service 的 onBind()方法 return 过来的 Binder 的子类。

MyService MainAcitivity

（二）Using a Messenger

MessengerService.java

public class MessengerService extends Service {

    private Messenger messenger = new Messenger(new IncomingHandler());
    private Messenger mActivityMessenger;


    @Override
    public IBinder onBind(Intent intent) {
        IBinder binder = messenger.getBinder();
        return binder;
    }

    class IncomingHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case 0:
                    Log.d("tag", msg.toString());
                    if (mActivityMessenger != null) {
                        Message message = new Message();
                        message.what = 2;
                        message.obj = "地瓜地瓜我是土豆";
                        try {
                            mActivityMessenger.send(message);
                        } catch (RemoteException e) {
                            e.printStackTrace();
                        }
                    }
                    break;

                case 1:
                    mActivityMessenger = (Messenger) msg.obj;
                    Log.d("tag", "已经获取到 Activity 发送了的 Messenger 对象");
                    break;

                default:
                    break;

            }
        }
    }
}

MessageActivity.java

public class MessageActivity extends AppCompatActivity {

    private Messenger messenger;
    private Messenger mOutMessenger = new Messenger(new OutgoingHandler());

    private ServiceConnection conn = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            Toast.makeText(MessageActivity.this, "连接成功！", Toast.LENGTH_SHORT).show();
            messenger = new Messenger(service);
            Message message = new Message();
            message.what = 1;
            message.obj = mOutMessenger;
            try {
                messenger.send(message);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            Toast.makeText(MessageActivity.this, "连接已经断开！", Toast.LENGTH_SHORT).show();
        }
    };


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_message);
    }

    /**
     * 绑定服务
     *
     * @param view
     */
    public void click1(View view) {
        Intent intent = new Intent(this, MessengerService.class);
        bindService(intent, conn, BIND_AUTO_CREATE);
    }

    /**
     * 发送消息
     *
     * @param view
     */
    public void click2(View view) {
        if (messenger == null) {
            Toast.makeText(this, "服务不可用！", Toast.LENGTH_SHORT).show();
            return;
        }
        Message message = new Message();
        message.obj = "长江长江我是黄河";
        message.what = 0;
        try {
            messenger.send(message);
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }

    class OutgoingHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            Log.d("tag", msg.toString());
        }
    }
}

（三）Using AIDL

AIDL 比较适合当客户端和服务端不在同一个应用下的场景。
有点多啊哈哈哈，可以看这篇IPC机制——AIDL的简单梳理