ArrayList объектов в методе во FragmentB равен нулю, когда вызывается метод reply (page) в MainActivity

Question

1) Когда приложение запускается в ландшафтном режиме, после создания фрагмента A начинается формирование фрагмента B с помощью метода response () mainActivity. И после того, как он заканчивается и его видимость проверяется, вызывается changeData (index). Но ArrayList объектов во FragmentB является нулевым, когда вызывается метод changeData.

2) Также не работает переход из пейзажа в портрет или наоборот. Соответствующие макеты работают в репрезентативной ориентации, но во время перехода приложение закрывается. MainActivity:

public class MainActivity extends AppCompatActivity implements FragmentA.Communicator{

FragmentB f2;
ArrayList<Book> b = new ArrayList<Book>();
FragmentManager manager;
static int flag = 0;
static String search="great";
SearchView sv ;





@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    sv = (SearchView) findViewById(R.id.searchView);
    sv.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextSubmit(String query) {
            flag = 1;
            search = query;
            getBooks();
            return false;
        }

        @Override
        public boolean onQueryTextChange(String newText) {
            getBooks();
            return false;
        }
    });

    // TODO - add logic to auto-select first book in list to display in details fragment when running in landscape mode
    // TODO - add logic to figure out whether app is displaying in landscape or poortrait mode to accomplish ^^

    getBooks();
    /*
    manager = getSupportFragmentManager();
    f1 = (FragmentA) manager.findFragmentById(R.id.fragment);
    f1.setCommunicator(this);*/

}


@Override
public void respond(int index) {

    /*Bundle args = new Bundle();
    args.putSerializable("book_b_array", (ArrayList<Book>) b);
    args.putInt("someInt",index);
    */

    //f2.setArguments(args);
    Bundle args = new Bundle();
    args.putSerializable("book_b_array", (ArrayList<Book>) b);
    args.putInt("someInt",index);
    FragmentB f2 = (FragmentB) manager.findFragmentById(R.id.fragment2);
    f2.setArguments(args);
    /*FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.add(R.id.fragment2,f2);
    transaction.commit();*/

    if(f2!=null && f2.isVisible())
    {

        f2.changeData(index);
    }
    else
    {
        Bundle bundle = new Bundle();
        bundle.putInt("index", index);
        bundle.putSerializable("bookarray",(ArrayList<Book>)b);
        Fragment newFragment = new FragmentC();
        newFragment.setArguments(bundle);
        FragmentTransaction transaction2 = getSupportFragmentManager().beginTransaction();
        transaction2.replace(R.id.fragment, newFragment);
        transaction2.addToBackStack(null);
        transaction2.commit();


    }
}

public void afterGetBooks(ArrayList<Book> bks) {
    b.clear();
    for (Book h : bks) {
        b.add(h);
    }
    manager = getSupportFragmentManager();
    Bundle args = new Bundle();
    args.putSerializable("bookarray",(ArrayList<Book>)bks);
    FragmentA f1 = new FragmentA();
    f1.setArguments(args);
    FragmentTransaction transaction1 = manager.beginTransaction();
    transaction1.replace(R.id.fragment,f1);
    transaction1.addToBackStack(null);
    transaction1.commit();
    f1.setCommunicator(this);


}

private void getBooks(){

    String url;
    if(flag==0){
    url = "https://kamorris.com/lab/audlib/booksearch.php/";}
    else{
        url = "https://kamorris.com/lab/audlib/booksearch.php?search=" + search;
        flag=0;
    }
    //ArrayList<Book> boo;

    Retrofit retrofit =  new Retrofit.Builder().baseUrl("https://kamorris.com/lab/audlib/booksearch.php/").addConverterFactory(GsonConverterFactory.create()).build();

    Book.API api = retrofit.create(Book.API.class);

    Call<ArrayList<Book>> call = api.getBooks(url);
    call.enqueue(new Callback<ArrayList<Book>>() {
        @Override
        public void onResponse(Call<ArrayList<Book>> call, Response<ArrayList<Book>> response) {

            ArrayList<Book> Books = response.body();
            for(Book h: Books){
                Log.d("Retro-Title",h.getTitle());
                //b.add(h);
            }
            afterGetBooks(Books);
        }

        @Override
        public void onFailure(Call<ArrayList<Book>> call, Throwable t) {
            Toast.makeText(getApplicationContext(),t.getMessage(),Toast.LENGTH_SHORT).show();
        }
    });


}
}

Fragmenta:

public class FragmentA extends Fragment implements AdapterView.OnItemClickListener{

ListView list;
Communicator communicator;
ArrayList<Book> book_a;
ArrayList<String>  book_titles;


@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view= inflater.inflate(R.layout.fragment_a,container,false);
    savedInstanceState = getArguments();
    if (getArguments() != null) {
        // savedInstanceState = getArguments();
        book_a = (ArrayList<Book>) getArguments().getSerializable("bookarray");
        book_titles = getList(book_a);
        //Log.d("Frag_a:Title",book_a.get(5).getTitle());
        list= (ListView) view.findViewById(R.id.listview);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),android.R.layout.simple_list_item_1,book_titles);
        list.setAdapter(adapter);
        list.setOnItemClickListener(this);
    }
    return view;
}


public ArrayList<String> getList(ArrayList<Book> book2){

    ArrayList<String> list_titles = new ArrayList<String>();
    int size = book2.size();
    for(int i=0;i<size;i++){
        Book object;
        object = book2.get(i);
        list_titles.add(object.title);
    }


    return list_titles;
}

public void setCommunicator(Communicator communicator)
{
    this.communicator = communicator;
}

@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
    communicator.respond(position);

}

public interface Communicator{
    public void respond(int index);
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    if(context instanceof Communicator){
        communicator = (Communicator) context;
    } else {
        throw new RuntimeException(context.toString()+"must implement Communicator");
    }

}

@Override
public void onDetach() {
    super.onDetach();
    communicator = null;
}
}

FragmentB:

public class FragmentB extends Fragment {

private int page;
TextView text;
ArrayList<Book> book_b;
boolean fl=false;




public static  FragmentB newInstance(ArrayList<Book> b,int page){
    FragmentB f2 = new FragmentB();
    Bundle args = new Bundle();
    args.putSerializable("book_b_array",b);
    args.putInt("someInt",page);
    f2.setArguments(args);
    return f2;
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    if (getArguments() != null){
        book_b = (ArrayList<Book>) getArguments().getSerializable("book_b_array");
        page = getArguments().getInt("someInt",0);
    } else{ page = 0; fl=true;}
}

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

    View view = inflater.inflate(R.layout.fragment_b,container,false);
    text = (TextView) view.findViewById(R.id.textview);
    changeData(page);
    return view;
}

public void changeData(int index)
{
    if(fl==false) {
        String description = book_b.get(index).getTitle();
        text.setText(description);
    }
    else{
        text.setText("Select a Book to Display Data");
        fl=false;
    }

}
}