EventBusSupport.java

/**
 * @author chris.jenkins
 * @created Dec 4, 20124:06:20 PM
 */
package com.example.android.util;

import java.util.HashMap;
import java.util.Map;

import android.app.Activity;

import de.greenrobot.event.EventBus;

/**
 * @author chris.jenkins
 */
public class EventBusSupport {

    private static final Map<Activity, EventBus> mActivityBus = new HashMap<Activity, EventBus>();

    // private static final Map<Activity, List<Object>> mActivityLinks = new HashMap<Activity, List<Object>>();

    /**
     * Creates a unique event bus for the current activity, useful for fragments to call. Calling {@link #removeActivityBus(Activity)} will remove the
     * instance of the bus and call {@link #getActivityBus(Activity)} again will create a new one.
     * 
     * 
     * @author chris.jenkins
     * @param activity
     * @return
     */
    public synchronized static EventBus getActivityBus(final Activity activity) {
        if (activity == null) {
            throw new InstantiationError("Activity is null");
        }
        final EventBus bus = findBus(activity);
        return bus;
    }

    /**
     * I would only recommend calling this in onDestroy of the {@link Activity} not in the fragments, I could add registering but for simplicity and
     * efficenty its better to just trak the activity object.
     * 
     * @author chris.jenkins
     * @param activity
     */
    public synchronized static void removeActivityBus(final Activity activity) {
        if (activity == null) {
            throw new InstantiationError("Activity is null");
        }
        removeBus(activity);
    }

    /**
     * Will find or create a unique bus for the activity
     * 
     * @author chris.jenkins
     * @param activity
     * @return
     */
    private static EventBus findBus(final Activity activity) {
        if (!mActivityBus.containsKey(activity)) {
            mActivityBus.put(activity, new EventBus());
        }
        return mActivityBus.get(activity);
    }

    private static void removeBus(final Activity activity) {
        if (mActivityBus.containsKey(activity)) {
            mActivityBus.remove(activity);
        }
    }

    private EventBusSupport() {
    }
}

ExampleActivity.java

class ExampleActivity {
 
    /**
     * Make sure we unregister the bust as to not maintain unessary reference to the activity or the bus
     */
    @Override
    protected void onDestroy() {
        EventBusSupport.removeActivityBus(this);
        super.onDestroy();
    }
  
}

ExampleFragment.java

public abstract class BaseFragment extends SherlockFragment {
  
    protected EventBus mBus;
  
    @Override
    public void onAttach(final Activity activity) {
        super.onAttach(activity);
        mActionBar = getSherlockActivity().getSupportActionBar();

        if (hasContextAwareEventBus()) {
            mBus = EventBusSupport.getActivityBus(activity);
        } else {
            mBus = EventBus.getDefault();
        }
    }
    
    /**
     * Override with true if you want this fragment to use the {@link EventBus} tied to the activity instead of the global one
     * 
     * @author chris.jenkins
     * @return
     */
    protected boolean hasContextAwareEventBus() {
        return false;
    }
  
}