How does eventbus register the onevent method befo

Question

The listItemFragment post an event to the ItemDetailFragment to refresh the UI. BUt the ItemDetailFragment is never used before, so the register() method in ItemDetailFragment is never invoked. So I want to know how the posted event in listItemFragment know the onevent method in ItemDetailFragment. Here is the source code:

package com.angeldevil.eventbusdemo;

import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import com.angeldevil.eventbusdemo.Event.ItemListEvent;

import de.greenrobot.event.EventBus;

public class ItemListFragment extends ListFragment
{

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    // Register
    EventBus.getDefault().register(this);
}

@Override
public void onDestroy()
{
    super.onDestroy();
    // Unregister
    EventBus.getDefault().unregister(this);
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState)
{
    super.onViewCreated(view, savedInstanceState);

    new Thread()
    {
        public void run()
        {
            try
            {
                Thread.sleep(2000); 

                EventBus.getDefault().post(new ItemListEvent(Item.ITEMS));
            } catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        };
    }.start();
}

public void onEventMainThread(ItemListEvent event)
{
    setListAdapter(new ArrayAdapter<Item>(getActivity(),
            android.R.layout.simple_list_item_activated_1,
            android.R.id.text1, event.getItems()));
}

@Override
public void onListItemClick(ListView listView, View view, int position,
        long id)
{
    super.onListItemClick(listView, view, position, id);
    EventBus.getDefault().post(getListView().getItemAtPosition(position));
}

 }


ItemDetailFragment:

package com.angeldevil.eventbusdemo;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import de.greenrobot.event.EventBus;

    public class ItemDetailFragment extends Fragment
{

private TextView tvDetail;

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    // register
    EventBus.getDefault().register(this);
}

@Override
public void onDestroy()
{
    super.onDestroy();
    // Unregister
    EventBus.getDefault().unregister(this);
}


public void onEventMainThread(Item item)
{
    if (item != null)
        tvDetail.setText(item.content);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState)
{
    View rootView = inflater.inflate(R.layout.fragment_item_detail,
            container, false);
    tvDetail = (TextView) rootView.findViewById(R.id.item_detail);
    return rootView;
}
}

Answer 1

The GreenRobot EventBus uses reflection to find methods called onEvent and delivers the event object to those with a matching signature.