Implementation of Load More feature for RecyclerView

LoadMoreAdapter.java

import android.support.v7.widget.RecyclerView;
import android.view.ViewGroup;
import java.util.ArrayList;
import java.util.List;

public abstract class LoadMoreAdapter<T>
    extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

  public static final int VIEW_TYPE_LOAD_MORE = 1;

  private List<T> items = new ArrayList<>();
  private boolean enableLoadMore;

  public void setEnableLoadMore(boolean enableLoadMore) {
    if (this.enableLoadMore == enableLoadMore) {
      return;
    }
    this.enableLoadMore = enableLoadMore;
    notifyDataSetChanged();
  }

  public void setItems(List<T> items) {
    this.items.clear();
    addItems(items);
  }

  public void addItems(List<T> items) {
    this.items.addAll(items);
    notifyDataSetChanged();
  }

  public T getItem(int position) {
    if (position < 0 || position > items.size() - 1) {
      return null;
    }
    return items.get(position);
  }

  @Override public int getItemCount() {
    return items == null ? 0 : items.size() + (enableLoadMore ? 1 : 0);
  }

  @Override public int getItemViewType(int position) {
    if (enableLoadMore && position == getItemCount() - 1) {
      return VIEW_TYPE_LOAD_MORE;
    }
    return super.getItemViewType(position);
  }

  @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType == VIEW_TYPE_LOAD_MORE) {
      return onCreateLoadMoreViewHolder(parent);
    }
    return onCreateItemViewHolder(parent, viewType);
  }

  @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    if (!enableLoadMore || position != getItemCount() - 1) {
      onBindItemViewHolder(holder, position);
    }
  }

  public boolean isEnableLoadMore() {
    return enableLoadMore;
  }

  public abstract RecyclerView.ViewHolder onCreateItemViewHolder(ViewGroup parent, int viewType);

  public abstract void onBindItemViewHolder(RecyclerView.ViewHolder holder, int position);

  public abstract RecyclerView.ViewHolder onCreateLoadMoreViewHolder(ViewGroup parent);

}

OnVerticalScrollListener.java

import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

public abstract class OnVerticalScrollListener extends RecyclerView.OnScrollListener {

  private boolean lastItemVisible;

  @Override public final void onScrolled(RecyclerView recyclerView, int dx, int dy) {
    if (!recyclerView.canScrollVertically(-1)) {
      onScrolledToTop();
    } else if (!recyclerView.canScrollVertically(1)) {
      onScrolledToBottom();
    } else if (dy < 0) {
      onScrolledUp();
      lastItemVisible = isLastItemVisible(recyclerView);
    } else if (dy > 0) {
      onScrolledDown();
      boolean isLastItemVisible = isLastItemVisible(recyclerView);
      if (lastItemVisible != isLastItemVisible) {
        lastItemVisible = isLastItemVisible;
        if (lastItemVisible) {
          onScrolledDownToLastItem();
        }
      }
    }
  }

  private boolean isLastItemVisible(RecyclerView recyclerView) {
    if (recyclerView.getLayoutManager() instanceof LinearLayoutManager) {
      final int lastVisibleItemPosition =
          ((LinearLayoutManager) recyclerView.getLayoutManager()).findLastVisibleItemPosition();
      return lastVisibleItemPosition == recyclerView.getAdapter().getItemCount() - 1;
    }
    return false;
  }

  public void onScrolledDownToLastItem() {
  }

  public void onScrolledUp() {
  }

  public void onScrolledDown() {
  }

  public void onScrolledToTop() {
  }

  public void onScrolledToBottom() {
  }
}

SupportLoadMoreGridLayoutManager.java

import android.content.Context;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;

public class SupportLoadMoreGridLayoutManager extends GridLayoutManager {

  private SpanSizeLookupWrapper spanSizeLookupWrapper;
  private LoadMoreAdapter adapter;
  private Runnable computeLoadMore = new Runnable() {
    @Override public void run() {
      final int firstCompletelyVisibleItemPosition = findFirstCompletelyVisibleItemPosition();
      final int lastCompletelyVisibleItemPosition = findLastCompletelyVisibleItemPosition();
      if (firstCompletelyVisibleItemPosition < 0 || lastCompletelyVisibleItemPosition < 0) {
        return;
      }

      final boolean allVisible = firstCompletelyVisibleItemPosition == 0
          && lastCompletelyVisibleItemPosition == adapter.getItemCount() - 1;
      if (allVisible) {
        // All visible then we don't need to show load more
        spanSizeLookupWrapper.setLoadMorePosition(-1);
      } else {
        spanSizeLookupWrapper.setLoadMorePosition(adapter.getItemCount() - 1);
      }
      adapter.setEnableLoadMore(!allVisible);
    }
  };;

  public SupportLoadMoreGridLayoutManager(Context context, int spanCount) {
    this(context, spanCount, VERTICAL, false);
  }

  public SupportLoadMoreGridLayoutManager(Context context, int spanCount, int orientation,
      boolean reverseLayout) {
    super(context, spanCount, orientation, reverseLayout);
    spanSizeLookupWrapper = new SpanSizeLookupWrapper(spanCount);
    super.setSpanSizeLookup(spanSizeLookupWrapper);
  }

  @Override public void setSpanSizeLookup(SpanSizeLookup spanSizeLookup) {
    spanSizeLookupWrapper.setPlugIn(spanSizeLookup);
  }

  @Override public void onItemsChanged(final RecyclerView recyclerView) {
    super.onItemsChanged(recyclerView);
    final RecyclerView.Adapter adapter = recyclerView.getAdapter();
    if (!(adapter instanceof LoadMoreAdapter)) {
      throw new IllegalArgumentException("adapter must be instance of LoadMoreAdapter");
    }
    this.adapter = (LoadMoreAdapter) adapter;
    // Remove the old to keep only one callback execute.
    recyclerView.removeCallbacks(computeLoadMore);
    recyclerView.post(computeLoadMore);
  }

  static class SpanSizeLookupWrapper extends SpanSizeLookup {

    private final int spanCount;
    private SpanSizeLookup plugIn;
    private int loadMorePosition = -1;

    public SpanSizeLookupWrapper(int spanCount) {
      this.spanCount = spanCount;
    }

    public void setLoadMorePosition(int loadMorePosition) {
      this.loadMorePosition = loadMorePosition;
    }

    public void setPlugIn(SpanSizeLookup plugIn) {
      this.plugIn = plugIn;
    }

    @Override public void invalidateSpanIndexCache() {
      super.invalidateSpanIndexCache();
      loadMorePosition = -1;
    }

    @Override public int getSpanSize(int position) {
      final int spanSize;
      if (loadMorePosition == position) {
        spanSize = this.spanCount;
        return spanSize;
      } else if (plugIn != null) {
        spanSize = plugIn.getSpanSize(position);
      } else {
        spanSize = 1;
      }
      return spanSize;
    }
  }

}

SupportLoadMoreLinearLayoutManager.java

import android.content.Context;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

public class SupportLoadMoreLinearLayoutManager extends LinearLayoutManager {

  private LoadMoreAdapter adapter;
  private Runnable computeLoadMore = new Runnable() {
    @Override public void run() {
      final int firstCompletelyVisibleItemPosition = findFirstCompletelyVisibleItemPosition();
      final int lastCompletelyVisibleItemPosition = findLastCompletelyVisibleItemPosition();
      if (firstCompletelyVisibleItemPosition < 0 || lastCompletelyVisibleItemPosition < 0) {
        return;
      }

      final boolean allVisible = firstCompletelyVisibleItemPosition == 0
          && lastCompletelyVisibleItemPosition == adapter.getItemCount() - 1;
      adapter.setEnableLoadMore(!allVisible);
    }
  };

  public SupportLoadMoreLinearLayoutManager(Context context, int orientation,
      boolean reverseLayout) {
    super(context, orientation, reverseLayout);
  }

  @Override public void onItemsChanged(final RecyclerView recyclerView) {
    super.onItemsChanged(recyclerView);
    final RecyclerView.Adapter adapter = recyclerView.getAdapter();
    if (!(adapter instanceof LoadMoreAdapter)) {
      throw new IllegalArgumentException("adapter must be instance of LoadMoreAdapter");
    }
    this.adapter = (LoadMoreAdapter) adapter;
    // Remove the old to keep only one callback execute.
    recyclerView.removeCallbacks(computeLoadMore);
    recyclerView.post(computeLoadMore);
  }

}