BaseActivity.java

package com.squareup.example;

public abstract BaseActivity extends SherlockActivity {
  private final ScopedBus scopedBus = new ScopedBus();

  protected ScopedBus getBus() {
    return scopedBus;
  }

  @Override public void onPause() {
    super.onPause();
    bus.paused();
  }

  @Override public void onResume() {
    super.onResume();
    bus.resumed();
  }
}

ScopedBus.java

package com.squareup.example;

public class ScopedBus {
  // See Otto's sample application for how BusProvider works. Any mechanism
  // for getting a singleton instance will work.
  private final Bus bus = BusProvider.get();
  private final Set<Object> objects = new HashSet<Object>();
  private boolean active;

  public void register(Object obj) {
    objects.add(obj);
    if (active) {
      bus.register(obj);
    }
  }

  public void unregister(Object obj) {
    objects.remove(obj);
    if (active) {
      bus.unregister(obj);
    }
  }

  public void post(Object event) {
    bus.post(event);
  }

  void paused() {
    active = false;
    for (Object obj : objects) {
      bus.unregister(obj);
    }
  }

  void resumed() {
    active = true;
    for (Object obj : objects) {
      bus.register(obj);
    }
  }
}