通信方式

1. binder + 回调(listener)

主要思路：Acitivity 将实例传入 Service，同时利用回调更新UI

2. binder + Handler

主要思路：Service 持有 Activity的Handler 对象，Service 通过往该Handler send message 的方式，达到通信的目的。

3. 广播 （推荐LocalBroadcastManager）

主要思路：利用系统的LocalBroadcastManager，Service send message， Activity receive message；

4. 开源组件(EventBus，otto)

主要思路：利用反射或者注释的方式实现对注册类的注册，然后遍历当前的注册表，通过key进行查询，然后dispatch，调用相应的事件处理方法。（不同的开源框架实现有所区别）

5. AIDL

主要思路：//TODO

总结

目前Android 组件之间主流的通信方式如上所述的5种，哪种对于项目更加合适，需要考虑的适用情况有：

1. 进程内通信还是进程间通信
2. 一对一通信，还是一对多
3. 单向还是双向
4. 性能
5. 其他(安全性，代码可读性，实现复杂性)等等；

源代码(通信方式1、2、3、4 Demo)

public class MainActivity extends Activity implements View.OnClickListener, OnProgressListener, Handler.Callback{

private DownloadService mDownloadService;
private ProgressBar mProgressBar;

private LocalBroadcastManager mLocalBroadcastManager;

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

    mProgressBar = (ProgressBar)findViewById(R.id.progressBar);
    findViewById(R.id.button1).setOnClickListener(this);
    findViewById(R.id.button2).setOnClickListener(this);

    Intent intent = new Intent("com.example.downloadservice");
    bindService(intent, serviceConnection, BIND_AUTO_CREATE);

    mLocalBroadcastManager = LocalBroadcastManager.getInstance(this);

    EventBus.getDefault().register(this);
}

@Override
protected void onResume() {
    super.onResume();

    mLocalBroadcastManager.registerReceiver(mBroadcastReceiver, new IntentFilter("from_downloadService"));
}

@Override
protected void onDestroy() {
    unbindService(serviceConnection);
    mLocalBroadcastManager.unregisterReceiver(mBroadcastReceiver);
    EventBus.getDefault().unregister(this);
    super.onDestroy();
}

/**
 * 通信方式四：第三方开源组件eventbus
 * @param progressEvent
 */
public void onEvent(ProgressEvent progressEvent) {
    mProgressBar.setProgress(progressEvent.getProgress());
}

/**
 * 通信方式一
 * @param progress
 */
@Override
public void OnProgress(int progress) {
    mProgressBar.setProgress(progress);
}


/**
 * 通信方式二
 * @param message
 */
@Override
public boolean handleMessage(Message message) {
    mProgressBar.setProgress(message.what);
    return false;
}

@Override
public void onClick(View view) {
    int id = view.getId();
    switch (id) {
        case R.id.button1:
            mDownloadService.startDownload();
            break;
        case R.id.button2:
            break;
        default:
            break;
    }
}

ServiceConnection serviceConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
        mDownloadService = ((DownloadService.MsgBinder) iBinder).getService();

        /**
         * 通信方式一
         */
        /*if (mDownloadService != null) {
            mDownloadService.setOnProgressListener(MainActivity.this);
        }*/

        /**
         * 通信方式二
         * //TODO:考虑内存泄露
         */
        /*if (mDownloadService != null) {
            mDownloadService.setHandler(new Handler(MainActivity.this));
        }*/
    }

    @Override
    public void onServiceDisconnected(ComponentName componentName) {
    }
};

/**
 * 通信方式三
 */
BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        mProgressBar.setProgress(intent.getIntExtra("KEY_PROGRESS", -1));
    }
};
}

=================================

public class DownloadService extends Service {

public final static int MAX_PROGRESS = 100;

private int mProgress = 0;

private OnProgressListener mOnProgressListener;

private Handler mHandler;

public DownloadService() {
}

@Override
public IBinder onBind(Intent intent) {
    return new MsgBinder();
}

/**
 * 通信方式一：通过回调的方式
 * @param onProgressListener
 */
public void setOnProgressListener(OnProgressListener onProgressListener) {
    this.mOnProgressListener = onProgressListener;
}

/**
 * 通信方式二：通过持有Activity handler的方式
 * @param handler
 */
public void setHandler(Handler handler) {
    this.mHandler = handler;
}

/**
 * //TODO:考虑并发性
 */
public void startDownload() {
    new Thread(new Runnable() {
        @Override
        public void run() {
            while (mProgress < MAX_PROGRESS) {
                mProgress += 5;

                /**
                 * 通信方式一
                 */
                /*if (mOnProgressListener != null) {
                    mOnProgressListener.OnProgress(mProgress);
                }*/

                /**
                 * 通信方式二
                 */
                /*if (mHandler != null) {
                    Message message = new Message();
                    message.what = mProgress;
                    mHandler.sendMessage(message);
                }*/


                /**
                 * 通信方式三
                 */
                /*Intent intent = new Intent("from_downloadService");
                intent.putExtra("KEY_PROGRESS", mProgress);
                LocalBroadcastManager.getInstance(DownloadService.this).sendBroadcast(intent);*/

                EventBus.getDefault().post(new ProgressEvent(mProgress));

                try {
                    Thread.sleep(1000);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    }).start();
}

public class MsgBinder extends Binder {

    public DownloadService getService() {
        return DownloadService.this;
    }
}
}

===========================

public interface OnProgressListener {
    void OnProgress(int progress);
}

===========================

public class ProgressEvent {
public ProgressEvent(int mProgress) {
    this.mProgress = mProgress;
}

public int getProgress() {
    return mProgress;
}

public void setProgress(int mProgress) {
    this.mProgress = mProgress;
}

private int mProgress = 0;

}

参考

[相关讨论]
http://stackoverflow.com/questions/2463175/how-to-have-android-service-communicate-with-activity
[相关讨论]
http://stackoverflow.com/questions/20594936/communication-between-activity-and-service
[LocalBroadcastManager官方参考]
http://developer.android.com/reference/android/support/v4/content/LocalBroadcastManager.html
[EventBus源码详解]
https://github.com/android-cn/android-open-project-analysis/tree/master/tool-lib/event-bus/event-bus
[EventBus 与otto应用和性能对比]
http://timnew.me/blog/2014/09/14/otto-and-android-annotations-compatibility-issue-analysis/
[EventBus 与otto源码实现对比]
http://frodoking.github.io/2015/03/30/android-eventbus-otto-analysis/
[其他]
1.http://developer.samsung.com/technical-doc/view.do;jsessionid=vF09VyrXngrTLTX9f2gfn2zvP2GjTSqs1T91GWF31PNhHvlBc2gv!-1892717541?v=T000000087
2.http://developer.android.com/reference/android/app/Service.html#RemoteMessengerServiceSample
3.http://developer.android.com/guide/components/bound-services.html
4.http://www.jikexueyuan.com/blog/308.html
5.http://blog.philippheckel.com/2012/06/10/android-example-communication-between-activity-and-service-using-messaging/
6.http://blog.csdn.net/xiaanming/article/details/9750689
7.https://androidexperinz.wordpress.com/2012/02/21/communication-between-service-and-activity-part-2/