如何根据微调器选择MVVM + LiveData更新recyclerview

Question

I have an Android app (Java) that uses MVVM + LiveData to display a list of shows by season. I want season 1 titles to display in a RecyclerView when the user first lands on the fragment. I then want the user to be able to select another season and then display those titles. I'm able to send the selected season to my ViewModel, but I don't know how to update my RecyclerView with the selected season's titles. Any help is greatly appreciated!

Here is my fragment:

    public class ShowFragment extends Fragment {
        private ShowTitlesAdapter showTitlesAdapter;
        private ArrayList<Titles> titlesList;
    
        private FragmentShowBinding binding;
        private TitlesViewModel titlesViewModel;
        private String ShowTag, ShowTitle, ShowImgUrl;
        private RecyclerView rvTitles;
        private Spinner popupSpinner;
    
        public ShowFragment() {
            // Required empty public constructor
        }
    
    
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
        }
    
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            // Inflate the layout for this fragment
            binding = FragmentShowBinding.inflate(inflater, container, false);
            View view = binding.getRoot();
            return view;
        }
    
        @Override
        public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
            super.onViewCreated(view, savedInstanceState);
    
            titlesList = new ArrayList<>();
    
            titlesViewModel = new ViewModelProvider(this).get(TitlesViewModel.class);
            initAdapter();
            init();
    
            ShowFragmentArgs args = ShowFragmentArgs.fromBundle(getArguments());
            ShowTag = args.getFranchiseTag();
            titlesViewModel.getAllTitles(ShowTag);
    
            ShowImgUrl = args.getShowImg();
            ShowTitle = args.getShowTitle();
    
            titlesViewModel.getAllTitles(ShowTitle);
            binding.showTitle.setText(ShowTitle);
            Drawable placeHolder = getResources().getDrawable(R.drawable.placeholder_1080x1080);
    
            Glide.with(getContext())
                    .load(ShowImgUrl) //image url
                    .placeholder(placeHolder)
                    .into(binding.showImage);
        }
    
        private void initAdapter() {
            binding.rvTitles.setLayoutManager(new LinearLayoutManager(getContext()));
            showTitlesAdapter = new ShowTitlesAdapter(getContext(), titlesList);
            binding.rvTitles.setAdapter(showTitlesAdapter);
        }
    
    
        private void init() {
            titlesList.clear();
    
            titlesViewModel.sortedSeasonListOne.observe(getViewLifecycleOwner(), new Observer<List<Titles>>() {
                @Override
                public void onChanged(List<Titles> titles) {
                    titlesList.addAll(titles);
                    showTitlesAdapter.setShowTitlesList(titlesList);
                }
            });
            titlesViewModel.getAllTitles(ShowTag);
    
            createDropDownList(titlesList);
        }
    
    
        public void createDropDownList(ArrayList<Titles> titles) {
            List<String> seasonListStr = new ArrayList<>();
    
            titlesViewModel.seasonsStrList.observe(getViewLifecycleOwner(), new Observer<List<String>>() {
                @Override
                public void onChanged(List<String> seasons) {
                    seasonListStr.addAll(seasons);
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
                        seasonListStr.replaceAll(s -> "Season " + s);
                    }
                    ArrayAdapter<String> adapter = new ArrayAdapter<String>(getContext(), android.R.layout.simple_list_item_1, seasonListStr);
                    adapter.setDropDownViewResource(android.R.layout.simple_list_item_1);
                    binding.popupSpinner.setAdapter(adapter);
                    binding.popupSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
    
                        @Override
                        public void onItemSelected(AdapterView<?> parent, View view, int position, long l) {
                            titlesViewModel.populateTitlesInSeason(parent.getItemAtPosition(position).toString());
//                        showTitlesAdapter.setShowTitlesList(titlesList); --> I don't know how to update this list with another season of titles!
                        }
    
                        @Override
                        public void onNothingSelected(AdapterView<?> adapterView) {
                        }
                    });
                    binding.popupSpinner.setAdapter(adapter);
                }
            });
        }
    

        @Override
        public void onDestroyView() {
            super.onDestroyView();
            binding = null;
        }
    }

ViewModel:

public class TitlesViewModel extends ViewModel {
    Repository repository;
    private final io.reactivex.rxjava3.disposables.CompositeDisposable disposables = new CompositeDisposable();

    public MutableLiveData<ArrayList<Titles>> titlesListLiveData;
    public List<String> seasonsList;
    public LiveData<List<Titles>> sortedList;
    public LiveData<List<Titles>> sortedSeasonListOne;
    public LiveData<List<Titles>> sortedSeasonListSeason;
    public LiveData<List<Integer>> seasons;
    public LiveData<List<String>> seasonsStrList;


    @Inject
    public TitlesViewModel(Repository repository) {
        this.repository = repository;
        titlesListLiveData = repository.getTitlesLiveData();

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            sortedList = Transformations.map(titlesListLiveData, titlesList -> titlesList.stream().sorted(Comparator.comparing(Titles::getSeasonNumber).thenComparing(Titles::getEpisodeNumber)).collect(Collectors.toList()));
        }

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            seasons = Transformations.map(sortedList, list -> list.stream().map(Titles::getSeasonNumber).distinct().collect(Collectors.toList()));
            seasonsStrList = Transformations.map(seasons, strList -> strList.stream().map(Object::toString).collect(Collectors.toList()));
        }

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            sortedSeasonListOne = Transformations.map(titlesListLiveData, srtList -> srtList.stream().sorted(Comparator.comparing(Titles::getSeasonNumber).thenComparing(Titles::getEpisodeNumber)).filter(list ->1 == list.getSeasonNumber()).collect(Collectors.toList()));
        }

    }

    public void populateTitlesInSeason(String season) {
        String seasonNo = season.substring(7);
        int seasonNum = 1;
        try{
            seasonNum = Integer.parseInt(seasonNo);

        }catch(NumberFormatException ex){

        }


        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            int finalSeasonNum = seasonNum;
            sortedSeasonListSeason = Transformations.map(titlesListLiveData, seasonList -> seasonList.stream().sorted(Comparator.comparing(Titles::getSeasonNumber).thenComparing(Titles::getEpisodeNumber)).filter(list -> finalSeasonNum == list.getSeasonNumber()).collect(Collectors.toList()));
        }
    }

    /////////Titles
    public void getAllTitles(String tag) {
        repository.getAllTitles(tag);
    }


    @RequiresApi(api = Build.VERSION_CODES.N)
    public MutableLiveData<ArrayList<Titles>> getTitlesListLiveData() {
        return repository.getTitlesLiveData();
    }

    @Override
    protected void onCleared() {
        super.onCleared();
        disposables.clear();
    }
}

Repository:

public class Repository {

    final ApiService apiService;

    private final MutableLiveData<ArrayList<Titles>> titlesList = new MutableLiveData<>();

    @Inject
    public Repository(ApiService service){this.apiService = service;}

    public void getAllTitles(String tag){
        apiService.getTitles(tag).enqueue(new Callback<ArrayList<Titles>>() {

            @Override
            public void onResponse(Call<ArrayList<Titles>> call, Response<ArrayList<Titles>> response) {
                if (response.body() != null) {
                    titlesList.postValue(response.body());
                }
            }

            @Override
            public void onFailure(Call<ArrayList<Titles>> call, Throwable t) {
                Log.d("Titles","onFailure"+Thread.currentThread().getName());
            }
        });
    }

    public MutableLiveData<ArrayList<Titles>> getTitlesLiveData(){
        return titlesList;
    }

}

RecyclerView Adapter:

public class ShowTitlesAdapter extends RecyclerView.Adapter<ShowTitlesAdapter.ShowTitlesViewHolder> {
    private ItemShowTitleBinding binding;
    private ArrayList<Titles> showTitles;

    private Context context;
    int pos;

    public ShowTitlesAdapter(Context context, ArrayList<Titles> showTitles){
        this.context = context;
        this.showTitles = showTitles;
    }

    @NonNull
    @Override
    public ShowTitlesViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(context);
        binding = ItemShowTitleBinding.inflate(inflater, parent, false);
        return new ShowTitlesViewHolder(binding);
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    @Override
    public void onBindViewHolder(@NonNull ShowTitlesViewHolder holder, int position) {
        holder.binding.showTitleLayout.setClipToOutline(true);
        holder.binding.episodeNo.setText(Integer.toString(showTitles.get(position).getEpisodeNumber()));
        holder.binding.episodeTitle.setText(showTitles.get(position).getTitle());
        pos = position;
        holder.binding.showTitleLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ShowFragmentDirections.ActionShowFragmentToMovieShowDetailFragment action =
                        ShowFragmentDirections.actionShowFragmentToMovieShowDetailFragment(showTitles.get(position).getId(), showTitles.get(position).getFranchiseTag());
                Navigation.findNavController(v).navigate((NavDirections) action);
            }
        });
    }

    @Override
    public int getItemCount() {
        if(showTitles != null){
            return showTitles.size();
        }
        return 0;
    }

    public class ShowTitlesViewHolder extends RecyclerView.ViewHolder {

        private ItemShowTitleBinding binding;

        public ShowTitlesViewHolder(ItemShowTitleBinding binding) {
            super(binding.getRoot());
            this.binding = binding;

        }
    }

    public void setShowTitlesList(ArrayList<Titles> showTitles){
        this.showTitles = showTitles;
        notifyDataSetChanged();
    }

}

Answer 1

In short:

1. In ShowFragment you need to observe sortedSeasonListSeason of your TitlesViewModel
2. When you receive concrete season you should pass it to populateTitlesInSeason (you already do it)
3. Inside populateTitlesInSeason method you should pass your sortedSeasonListSeason list back to ShowFragment via MutableLiveData
4. So you need to create MutableLiveData for sortedSeasonListSeason list in TitlesViewModel to pass selected data, for example sortedSeasonListSeasonLiveData
5. So you need just sortedSeasonListSeasonLiveData.postValue(sortedSeasonListSeason)
6. Now back to ShowFragment and handle received list of concrete titles in observer from stage #1 of my instruction