事件总线OTTO（助Android深层次解耦——跟回调说拜拜）

 <! -- http://blog.csdn.net/yuanyang5917/article/details/45482457 -- >

事件总线框架

针对事件提供统一订阅，发布以达到组件间通信的解决方案。

官方定义：

       Otto is an event bus designed to decouple different parts of your application while still allowing them to communicate efficiently.

原理

观察者模式 + 注解 + 反射

Otto实现篇

这里要注意几点点：
（1）Otto使用注解定义订阅/发布者的角色，@Subscribe为订阅者，@Produce为发布者，方法名称就可以自定义了。
（2）Otto为了性能，代码意图清晰，@Subscribe，@Produce方法必须定义在直接的作用类上，而不能定义在基类而被继承。
（3）订阅者/发布者均需要register和unregister，而EventBus的发布者是不需要的。
（4）事件参数数量只可以有一个，不可更多

1. 定义事件-LocationChangedEvent ，作为组件间通信传递数据的载体

   /*
    * Copyright (C) 2012 Square, Inc.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    * http://www.apache.org/licenses/LICENSE-2.0
    *
    * Unless required by applicable law or agreed to in writing, software
    * distributed under the License is distributed on an "AS IS" BASIS,
    * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    * See the License for the specific language governing permissions and
    * limitations under the License.
    */
   
   package com.squareup.otto.sample;
   
   public class LocationChangedEvent {
     public final float lat;
     public final float lon;
   
     public LocationChangedEvent(float lat, float lon) {
       this.lat = lat;
       this.lon = lon;
     }
   
     @Override public String toString() {
       return new StringBuilder("(") //
           .append(lat) //
           .append(", ") //
           .append(lon) //
           .append(")") //
           .toString();
     }
   }
   
   

2. 避免浪费，相对于BusProvider.getInstance(), Otto需要自己实现单例。

   /*
    * Copyright (C) 2012 Square, Inc.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    * http://www.apache.org/licenses/LICENSE-2.0
    *
    * Unless required by applicable law or agreed to in writing, software
    * distributed under the License is distributed on an "AS IS" BASIS,
    * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    * See the License for the specific language governing permissions and
    * limitations under the License.
    */
   
   package com.squareup.otto.sample;
   
   import com.squareup.otto.Bus;
   
   /**
    * Maintains a singleton instance for obtaining the bus. Ideally this would be replaced with a more efficient means
    * such as through injection directly into interested classes.
    */
   public final class BusProvider {
     private static final Bus BUS = new Bus();
   
     public static Bus getInstance() {
       return BUS;
     }
   
     private BusProvider() {
       // No instances.
     }
   }
   
   

3. 定义订阅者，在接受事件的方法加上修饰符@Subscribe

   /*
    * Copyright (C) 2012 Square, Inc.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    * http://www.apache.org/licenses/LICENSE-2.0
    *
    * Unless required by applicable law or agreed to in writing, software
    * distributed under the License is distributed on an "AS IS" BASIS,
    * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    * See the License for the specific language governing permissions and
    * limitations under the License.
    */
   
   package com.squareup.otto.sample;
   
   import android.os.Bundle;
   import android.support.v4.app.ListFragment;
   import android.view.View;
   import android.widget.ArrayAdapter;
   import android.widget.Toast;
   
   import com.squareup.otto.Subscribe;
   
   import java.util.ArrayList;
   import java.util.List;
   
   /** Maintain a scrollable history of location events. */
   public class LocationHistoryFragment extends ListFragment {
       private final List<String> locationEvents = new ArrayList<String>();
       private ArrayAdapter<String> adapter;
   
       @Override
       public void onResume() {
           super.onResume();
           BusProvider.getInstance().register(this);
       }
   
       @Override
       public void onPause() {
           super.onPause();
           BusProvider.getInstance().unregister(this);
       }
   
       @Override
       public void onViewCreated(View view, Bundle savedInstanceState) {
           super.onViewCreated(view, savedInstanceState);
           adapter = new ArrayAdapter<String>(getActivity(),
                   android.R.layout.simple_list_item_1, locationEvents);
           setListAdapter(adapter);
       }
   
       @Subscribe
       public void onLocationChanged(LocationChangedEvent event) {
           locationEvents.add(0, event.toString());
           if (adapter != null) {
               adapter.notifyDataSetChanged();
           }
       }
   
       /**
        * 方法随便取，参数只能唯一
        * 很方便
        * @param event
        */
       @Subscribe
       public void turboLocationChanged(LocationChangedEvent event) {
           Toast.makeText(getActivity(), event.toString(), Toast.LENGTH_LONG)
                   .show();
       }
   
       @Subscribe
       public void onLocationCleared(LocationClearEvent event) {
           locationEvents.clear();
           if (adapter != null) {
               adapter.notifyDataSetChanged();
           }
       }
   }
   
   
   

4. 定义发布者，通过post()方法在任何地方发布消息了

   /*
    * Copyright (C) 2012 Square, Inc.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    * http://www.apache.org/licenses/LICENSE-2.0
    *
    * Unless required by applicable law or agreed to in writing, software
    * distributed under the License is distributed on an "AS IS" BASIS,
    * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    * See the License for the specific language governing permissions and
    * limitations under the License.
    */
   
   package com.squareup.otto.sample;
   
   import android.os.Bundle;
   import android.support.v4.app.FragmentActivity;
   import android.view.View;
   import com.squareup.otto.Produce;
   
   import java.util.Random;
   
   import static android.view.View.OnClickListener;
   
   public class LocationActivity extends FragmentActivity {
     public static final float DEFAULT_LAT = 40.440866f;
     public static final float DEFAULT_LON = -79.994085f;
     private static final float OFFSET = 0.1f;
     private static final Random RANDOM = new Random();
   
     private static float lastLatitude = DEFAULT_LAT;
     private static float lastLongitude = DEFAULT_LON;
   
     @Override protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.location_history);
   
       findViewById(R.id.clear_location).setOnClickListener(new OnClickListener() {
         @Override public void onClick(View v) {
           // Tell everyone to clear their location history.
           BusProvider.getInstance().post(new LocationClearEvent());
   
           // Post new location event for the default location.
           lastLatitude = DEFAULT_LAT;
           lastLongitude = DEFAULT_LON;
           BusProvider.getInstance().post(produceLocationEvent());
         }
       });
   
       findViewById(R.id.move_location).setOnClickListener(new OnClickListener() {
         @Override public void onClick(View v) {
           lastLatitude += (RANDOM.nextFloat() * OFFSET * 2) - OFFSET;
           lastLongitude += (RANDOM.nextFloat() * OFFSET * 2) - OFFSET;
           BusProvider.getInstance().post(produceLocationEvent());
         }
       });
     }
   
     @Override protected void onResume() {
       super.onResume();
   
       // Register ourselves so that we can provide the initial value.
       BusProvider.getInstance().register(this);
     }
   
     @Override protected void onPause() {
       super.onPause();
   
       // Always unregister when an object no longer should be on the bus.
       BusProvider.getInstance().unregister(this);
     }
   
     @Produce public LocationChangedEvent produceLocationEvent() {
       // Provide an initial value for location based on the last known position.
       return new LocationChangedEvent(lastLatitude, lastLongitude);
     }
   }
   
   

DOWNLOAD ADDRESS（DEMO下载地址）： http://download.csdn.net/download/yuanyang5917/8660175