使用翻新时滚动到RecyclerView的底部时添加更多项

Question

I was following this tutorial to implement pagination, and I was following it keenly, but I am uncertain how I should modify my current activity to implement OnLoadMoreListener . I am using an ApiService from retrofit to load data, unlike the tutorial that generates random strings.

This is how my current RecyclerView adapter looks like:

public class CuratedSectionAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private static int VIEW_TYPE_HEADER = 0;
    private static int VIEW_TYPE_ITEM = 1;
    private static int VIEW_TYPE_LOADING = 2;

    private int lastVisibleItem, totalItemCount;
    private int visibleThreshold = 2;
    private boolean isLoading;

    private List<Object> itemList;
    private OnLoadMoreListener onLoadMoreListener;

    public CuratedSectionAdapter(RecyclerView recyclerView, List<Object> itemList) {
        this.itemList = itemList;

        final LinearLayoutManager linearLayoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                totalItemCount = linearLayoutManager.getItemCount();
                lastVisibleItem = linearLayoutManager.findLastVisibleItemPosition();
                if (!isLoading && totalItemCount <= (lastVisibleItem + visibleThreshold)) {
                    if (onLoadMoreListener != null) {
                        onLoadMoreListener.onLoadMore();
                    }
                    isLoading = true;
                }
            }
        });
    }

    private class ItemViewHolder extends RecyclerView.ViewHolder {

        RecyclerView itemRecyclerView;
        CuratedSectionNestedAdapter nestedAdapter;
        LinearLayoutManager layoutManager;

        ItemViewHolder(View view) {
            super(view);
            itemRecyclerView = view.findViewById(R.id.recyclerView_nested);
            layoutManager = new LinearLayoutManager(view.getContext(), LinearLayoutManager.HORIZONTAL, false);
        }
    }

    private class HeaderViewHolder extends RecyclerView.ViewHolder {
        TextView textViewHeader;
        Typeface montserratMedium = Typeface.createFromAsset(getApplicationContext().getAssets(), "fonts/Montserrat-Medium.ttf");

        HeaderViewHolder(View view) {
            super(view);
            textViewHeader = view.findViewById(R.id.textView_header);
            textViewHeader.setTypeface(montserratMedium);
        }
    }

    private class LoadingViewHolder extends RecyclerView.ViewHolder {
        public ProgressBar progressBar;

        public LoadingViewHolder(View view) {
            super(view);
            progressBar = (ProgressBar) view.findViewById(R.id.progress_bar);
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {

        if (holder.getItemViewType() == VIEW_TYPE_HEADER) {
            HeaderViewHolder viewHolder = (HeaderViewHolder) holder;
            CuratedSectionHeader header = (CuratedSectionHeader) itemList.get(position);

            viewHolder.textViewHeader.setText(header.getHeaderName());
        } else if (holder.getItemViewType() == VIEW_TYPE_ITEM) {
            ItemViewHolder viewHolder = (ItemViewHolder) holder;
            List<CuratedSectionItem> items = (List<CuratedSectionItem>) itemList.get(position);

            if (viewHolder.nestedAdapter != null) {
                viewHolder.nestedAdapter.setItems(items);
            } else {
                viewHolder.nestedAdapter = new CuratedSectionNestedAdapter(items);
                viewHolder.itemRecyclerView.setLayoutManager(viewHolder.layoutManager);
                viewHolder.itemRecyclerView.setAdapter(viewHolder.nestedAdapter);
            }
        } else if (holder.getItemViewType() == VIEW_TYPE_LOADING) {
            LoadingViewHolder loadingViewHolder = (LoadingViewHolder) holder;
            loadingViewHolder.progressBar.setIndeterminate(true);
        }

    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType == VIEW_TYPE_HEADER) {
            return new HeaderViewHolder(LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.main_explore_header_row, parent, false));
        } else if (viewType == VIEW_TYPE_ITEM) {
            return new ItemViewHolder(LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.main_explore_row, parent, false));
        } else if (viewType == VIEW_TYPE_LOADING) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_loading, parent, false);
            return new LoadingViewHolder(view);
        }

        throw new RuntimeException("Adapter " + viewType + "not found");
    }

    @Override
    public int getItemCount() {
        return itemList.size();
    }

    @Override
    public int getItemViewType(int position) {

        if (itemList.get(position) instanceof  CuratedSectionHeader) {
            return VIEW_TYPE_HEADER;
        } else {
            return itemList.get(position) == null ? VIEW_TYPE_LOADING : VIEW_TYPE_ITEM;
        }
    }

    public void setOnLoadMoreListener(OnLoadMoreListener mOnLoadMoreListener) {
        this.onLoadMoreListener = mOnLoadMoreListener;
    }

    public void setLoaded() {
        isLoading = false;
    }
}

The current architecture of my activity uses private classes to make API calls and load the data. At the moment, all items are loaded at once, but ideally there should be only 2 items loaded at a time. I am uncertain how I should load additional items by calling the API service again when I scroll to the bottom. At the very least, I am certain that I will have to use curatedSectionAdapter.setOnLoadMoreListener somehow.

This is how I load all of the items at the moment:

private class Sections {
    List<CuratedSection> sections = new ArrayList<>();
    public Thread[] thread;

    private Sections() {}

    public void setSections(ArrayList<CuratedSection> sections) {
        this.sections = sections;
    }

    public void setSectionStories(String sectionId, List<CuratedSectionItem> stories) {
        for(CuratedSection s : sections){
            if(s.id != null && s.id.equals(sectionId)) {
                s.stories = stories;
            }
        }
    }

    public void loadStories(String sessionKey) {
        thread = new Thread[sections.size()];
        for( int s = 0; s < sections.size(); s++) {
            thread[s] = new Thread(new LoadStories(sessionKey, sections.get(s)));
            thread[s].start();
        }
        for( int f = 0; f < sections.size(); f++) {
            try {
                thread[f].join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        recyclerView.setLayoutManager(layoutManager);
        curatedSectionAdapter = new CuratedSectionAdapter(recyclerView, this.getAdapterInfo());
        recyclerView.setAdapter(curatedSectionAdapter);
    }

    public void loadSections(int numSections) {
        swipeRefreshLayout.setRefreshing(false);
        LoadSections load = new LoadSections(numSections);
        load.run();
    }

    public List<Object> getAdapterInfo() {
        List<Object> list = new ArrayList<>();

        for (int i = 0; i < sections.size(); i++) {
            CuratedSection section = sections.get(i);
            CuratedSectionHeader header = new CuratedSectionHeader();
            header.setHeaderName(section.header);

            list.add(header);
            list.add(section.stories);
        }

        return list;
    }
}


private class LoadSections implements Runnable {

    int numSections;

    LoadSections(int numSections) {
        this.numSections = numSections;
    }

    @Override
    public void run() {
        SharedPreferences prefs = getSharedPreferences("user_session", MODE_PRIVATE);
        final String sessionKey = prefs.getString("session_key", null);

        Call<JsonArray> call;
        call = TravelersApi.endpoint().getCuratedSections(sessionKey);

        call.enqueue(new Callback<JsonArray>() {
            @Override
            public void onResponse(Call<JsonArray> call, Response<JsonArray> response) {
                if(response.code() != 200) {
                    Toast.makeText(getApplicationContext(), "Cannot load page as of the moment.", Toast.LENGTH_SHORT).show();
                    return;
                }
                JsonArray rawSections = response.body();
                if(rawSections.size() == 0) {
                    //TODO: show placeholder
                    return;
                }
                ArrayList<CuratedSection> sections = new ArrayList<>();
                for(int i = 0; i < numSections; i++) {
                    JsonObject jSection = rawSections.get(i).getAsJsonObject();
                    final CuratedSection section = new CuratedSection();
                    section.id = jSection.get("id").getAsString();
                    section.header = jSection.get("section_header").getAsString();
                    section.topicCount = jSection.get("topic_count").getAsInt();
                    section.isShown = jSection.get("is_shown").getAsBoolean();
                    section.stories = new ArrayList<>();

                    sections.add(section);
                }
                curated.setSections(sections);
                curated.loadStories(sessionKey);

                spinner.clearAnimation();
                spinner.setVisibility(View.GONE);
                header.setVisibility(View.VISIBLE);
                swipeRefreshLayout.setVisibility(View.VISIBLE);

            }

            @Override
            public void onFailure(Call<JsonArray> call, Throwable t) {
                Log.d("ERROR!", t.toString());
                t.printStackTrace();
            }
        });
    }
}

Answer 1

You can achieve this by directly setting scroll listener to your recycler view.

recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            totalItemCount = linearLayoutManager.getItemCount();
            lastVisibleItem = linearLayoutManager.findLastVisibleItemPosition();
            if (!isLoading && totalItemCount <= (lastVisibleItem + visibleThreshold)) {
                // Call Load more method here to load next page data
               // Prevent multiple calls by using a boolean
                isLoading=true; // boolean to Prevent multiple calls
            }
        }
    });

OnLoadMoreListener is a interface you need to register it first. For pagination your server should process the pagination count. So you also need the api to perform on page limit .