事件总线OTTO（助Android深层次解耦——跟回调说拜拜）

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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

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();
  }
}

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.
  }
}

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();
        }
    }
}

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