Android Endless Scroll using RecyclerView

README.md

Endless Scroll Listener for Recycler Views

Endless Scrolling for Paginated APIs as shown in : Google Design - Progress Activity Behavior which has the following components:

1. Endless Scroll Listener for Recycler Views

• concrete class implements loadMore(pageNumber) to signal the API to load more data

2. List Adapter which shows:
   • Empty View when given an empty Item List (TextView)
   • Progress View when we are currently loading (ProgressBar)
   • addAll(...) to append data to the end of the list
   • setIsAppending(boolean) for signaling the start/end of data loading

Resources:

• https://github.com/codepath/android_guides/wiki/Endless-Scrolling-with-AdapterViews
• http://benjii.me/2010/08/endless-scrolling-listview-in-android/
• https://gist.github.com/ssinss/e06f12ef66c51252563e

EndlessListActivity.java

public class EndlessListActivity<D> extends Activity {
    private EndlessRecyclerOnScrollListener mEndlessScrollListener;
    private EndlessListAdapter mAdapter;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        RecyclerView listView = (RecyclerView) findViewById(R.id.list);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);

        mEndlessScrollListener = new EndlessRecyclerOnScrollListener(mLinearLayoutManager) {
            @Override
            public void onLoadMore(int current_page) {
                // try to get adapter from the recycler view, and cast it appropriately
                EndlessListAdapter adapter = (EndlessListAdapter) mListView.getAdapter();
                if (adapter != null) {
                    // signal adapter that loading attempt has started
                    adapter.setIsAppending(true);
                    adapter.notifyItemInserted(adapter.getItemCount());
                    
                    // Call your API Here
                    loadMore(current_page);
              }
          }
        };
    
        listView.setLayoutManager(linearLayoutManager);
        listview.addOnScrollListener(mEndlessScrollListener);
        
        // Do your RecyclerView stuff here
        mAdapter = new EndlessListAdapter(...);
    }
    
    // When your Data from the API is loaded,
    // set the Total Entries on your Endless Scroll Listener
    public void onDataLoaded(int serverTotalEntries) {
        mEndlessScrollListener.setTotalEntries(serverTotalEntries);
    }
    
    // After finishing loading of new data,
    // add it to your adapter
    public void onLoadMore(List<D> dataList) {
        mAdapter.addAll(dataList);
        mAdapter.setIsAppending(false);
    }
    
}

EndlessListAdapter.java

public abstract class EndlessListAdapter<VH extends RecyclerView.ViewHolder>
        extends RecyclerView.Adapter<VH> {
    private boolean mIsAppending = false;

    protected static final int VIEW_TYPE_PROGRESS = 333;

    public EndlessListAdapter(List<D> dataList) {
        super(dataList);
    }

    public boolean isAppending() {
        return mIsAppending;
    }

    public void setIsAppending(boolean isAppending) {
        mIsAppending = isAppending;
    }

    @Override
    public int getItemCount() {
        return isAppending() ?
                super.getItemCount() + 1 : super.getItemCount();
    }

    @Override
    public int getItemViewType(int position) {
        return (isAppending() && position >= super.getItemCount()) ?
                VIEW_TYPE_PROGRESS : super.getItemViewType(position);
    }

    @Override
    public final VH onCreateViewHolder(ViewGroup parent, int viewType) {
        RecyclerView.ViewHolder vh;
        if (viewType == VIEW_TYPE_PROGRESS) {
            View v = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.layout_progress_bar, parent, false);

            vh = new ProgressViewHolder(v);
        } else {
            vh = super.onCreateViewHolder(parent, viewType);
        }

        return (VH) vh;
    }

    @Override
    public final void onBindViewHolder(VH holder, int position) {
        if (holder instanceof ProgressViewHolder) {
            // do nothing
        } else {
            super.onBindViewHolder(holder, position);
        }
    }

    public static class ProgressViewHolder extends RecyclerView.ViewHolder {
        public ProgressViewHolder(View v) {
            super(v);
        }
    }

}

EndlessRecyclerOnScrollListener.java

public abstract class EndlessRecyclerOnScrollListener extends RecyclerView.OnScrollListener {
    private boolean mLoading = false; // True if we are still waiting for the last set of data to load
    
    private int previousItemCount = 0; // The total number of items in the dataset after the last load
    
    private int mTotalEntries; // The total number of entries in the server
    private int current_page = 1; // Always start at Page 1

    private LinearLayoutManager mLinearLayoutManager;

    public EndlessRecyclerOnScrollListener(LinearLayoutManager linearLayoutManager) {
        mLinearLayoutManager = linearLayoutManager;
    }
    
    // Concrete classes should implement the Loading of more data entries
    public abstract void onLoadMore(int current_page);

    public void setTotalEntries(int totalEntries) {
        mTotalEntries = totalEntries;
    }

    // when you're RecyclerView supports refreshing, also refresh the count
    public void refresh() {
        current_page = 1;
        previousItemCount = 0;
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        
        int visibleItemCount = recyclerView.getChildCount();
        int totalItemCount = mLinearLayoutManager.getItemCount();
        int firstVisibleItem = mLinearLayoutManager.findFirstVisibleItemPosition();

        if (mLoading) {
            int diffCurrentFromPrevious = totalItemCount - previousItemCount;

            // check if current total is greater than previous (diff should be greater than 1, for considering placeholder)
            // and if current total is equal to the total in server
            if ((diffCurrentFromPrevious > 1) ||
                    totalItemCount >= mTotalEntries) {
                mLoading = false;
                previousItemCount = totalItemCount;
            }
        } else {

            if (totalItemCount >= mTotalEntries) {
                // do nothing, we've reached the end of the list
            } else {
                // check if the we've reached the end of the list,
                // and if the total items is less than the total items in the server
                if ((firstVisibleItem + visibleItemCount) >= totalItemCount &&
                        totalItemCount < mTotalEntries) {
                    onLoadMore(++current_page);

                    mLoading = true;
                    previousItemCount = totalItemCount;
                }
            }
        }
    }

}

ListAdapter.java

public abstract class ListAdapter<D, VH extends RecyclerView.ViewHolder>
        extends RecyclerView.Adapter<VH> {
    protected List<D> mDataList;

    protected static final int VIEW_TYPE_NORMAL = 0;
    protected static final int VIEW_TYPE_EMPTY = 111;

    public ListAdapter(List<D> dataList) {
        mDataList = dataList;
    }

    @Override
    public int getItemCount() {
        return mDataList.isEmpty() ? 1 : mDataList.size();
    }

    @Override
    public int getItemViewType(int position) {
        if (mDataList.isEmpty()) {
            return VIEW_TYPE_EMPTY;
        } else {
            return VIEW_TYPE_NORMAL;
        }
    }

    public void clear() {
        int size = mDataList.size();
        mDataList.clear();
        notifyItemRangeRemoved(0, size);
    }

    public void addAll(List<D> data) {
        mDataList.addAll(data);
        notifyDataSetChanged();
    }

    protected D getItemAt(int position) {
        return mDataList.get(position);
    }

    protected D replaceItemAt(int position, D newItem) {
        D item = mDataList.set(position, newItem);
        notifyItemChanged(position);
        return item;
    }

    protected void addItem(int index, D newItem) {
        mDataList.add(index, newItem);
        notifyItemInserted(index);
    }

    protected void addItem(D newItem) {
        mDataList.add(newItem);
        notifyItemInserted(mDataList.size() - 1);
    }

    protected D removeItem(int index) {
        if (mDataList.size() > 0) {
            D item = mDataList.remove(index);
            notifyItemRemoved(index);

            return item;
        }

        return null;
    }

    @Override
    public VH onCreateViewHolder(ViewGroup parent, int viewType) {
        RecyclerView.ViewHolder vh;
        if (viewType == VIEW_TYPE_EMPTY) {
            View v = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.layout_empty_view, parent, false);

            vh = new EmptyViewHolder(v);
        } else {
            vh = createNormalViewHolder(parent, viewType);
        }

        return (VH) vh;
    }

    @Override
    public void onBindViewHolder(VH holder, int position) {
        if (holder instanceof EmptyViewHolder) {
            // do nothing
        } else {
            // Prevent binding of child view holder when List is NULL/Empty
            if (mDataList != null && !mDataList.isEmpty()) {
                bindNormalViewHolder(holder, position);
            }
        }
    }

    protected abstract VH createNormalViewHolder(ViewGroup parent, int viewType);

    protected abstract void bindNormalViewHolder(VH holder, int position);

    public static class EmptyViewHolder extends RecyclerView.ViewHolder {
        public EmptyViewHolder(View v) {
            super(v);
        }
    }
}