Passing an Object from an Activity to a Fragment

Create a static method in the Fragment and then get it using getArguments().

Example:

public class CommentsFragment extends Fragment {
  private static final String DESCRIBABLE_KEY = "describable_key";
  private Describable mDescribable;

  public static CommentsFragment newInstance(Describable describable) {
    CommentsFragment fragment = new CommentsFragment();
    Bundle bundle = new Bundle();
    bundle.putSerializable(DESCRIBABLE_KEY, describable);
    fragment.setArguments(bundle);

    return fragment;
  }

  @Override
  public View onCreateView(LayoutInflater inflater,
      ViewGroup container, Bundle savedInstanceState) {

    mDescribable = (Describable) getArguments().getSerializable(
        DESCRIBABLE_KEY);

    // The rest of your code
}

You can afterwards call it from the Activity doing something like:

FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
Fragment fragment = CommentsFragment.newInstance(mDescribable);
ft.replace(R.id.comments_fragment, fragment);
ft.commit();