viewpager fragments not receiving otto events from activity

Question

I have an activity with a Viewpager. my viewpager has several fragments. i want to send Otto event to a fragment when it is selected, thus i implement ViewPager.OnPageChangeListener

     @Override
  public void onPageSelected(int position) {
     currentPosition = position;
    switch (position){
      case 0:
        EventBus.getInstance().post(new TypeEvent());
        break;
      case 1:
        EventBus.getInstance().post(new InternalEvent());
        break;
    }
  }

Inside my first fragment

@Override
  public void onStart() {
    super.onStart();
  EventBus.getInstance().register(this);
  }

  @Override
  public void onStop(){
    super.onStop();
    EventBus.getInstance().unregister(this);
  }

  @Subscribe
  public void init(TypeEvent event){
    Logger.d("type event received");
    //do something.......
  }

My event bus class

    public class EventBus extends Bus {

   private static EventBus eventBus;

    public static EventBus getInstance(){
        if(eventBus == null){
          eventBus = new EventBus();
        }
        return eventBus;
      }
    }

The problem is my fragments are not receiving events. what could be the problem?

Answer 1

The issue was that onPageSelected(int position) method wasn't being called even after setting adapter on my viewpager and caling viewPager.setCurrentItem(0); in my activity onCreate(Bundle savedInstanceState) method.

@Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_pm);
    Toolbar toolbar =(Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    viewPager = (ViewPager)findViewById(R.id.pmViewpager);

    viewPager.addOnPageChangeListener(this);
    viewPager.setAdapter(new CustomAdapter(getSupportFragmentManager()));

    viewPager.setCurrentItem(currentPosition);
  }

i had to manually call onPageSelected(int position) through viewpager's post() method.

viewPager.post(new Runnable() {
          @Override
          public void run() {
            onPageSelected(viewPager.getCurrentItem());
          }
        });

Thus my overall onCreate(Bundle savedInstanceState) looked like this

@Override
      protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_pm);
        Toolbar toolbar =(Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        viewPager = (ViewPager)findViewById(R.id.pmViewpager);

        viewPager.addOnPageChangeListener(this);
        viewPager.setAdapter(new CustomAdapter(getSupportFragmentManager()));

        viewPager.setCurrentItem(currentPosition);

viewPager.post(new Runnable() {
              @Override
              public void run() {
                onPageSelected(viewPager.getCurrentItem());
              }
            });
      }

All other pages(fragments) are receiving the events because onpageSelected() will be called when on scroll away from the first page. it's only the first page that wasn't receiving the event.

Answer 2

Maybe when the event comes, the eventbus hasn't been registed yet, especilly at the Fragment's first initialization time.

So u can let EventBus.getInstance().register(this); be called at onAttach() and unregister at onDettach.