SectionedRecyclerViewAdapter

SectionedRecyclerViewAdapter.java

import android.support.annotation.Nullable;
import android.support.v4.util.ArrayMap;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.ViewGroup;
import java.util.List;

public abstract class SectionedRecyclerViewAdapter<VH extends RecyclerView.ViewHolder>
    extends RecyclerView.Adapter<VH> {

  private final static int VIEW_TYPE_HEADER = 0;
  private final static int VIEW_TYPE_ITEM = 1;

  private final ArrayMap<Integer, Integer> mHeaderLocationMap;
  private GridLayoutManager mLayoutManager;

  public SectionedRecyclerViewAdapter() {
    mHeaderLocationMap = new ArrayMap<>();
  }

  public abstract int getSectionCount();

  public abstract int getItemCount(int section);

  public abstract VH onCreateViewHolder(ViewGroup parent, boolean header);

  public abstract void onBindHeaderViewHolder(VH holder, int section);

  public void onBindHeaderViewHolder(VH holder, int section, List<Object> payload) {
    onBindHeaderViewHolder(holder, section);
  }

  public abstract void onBindViewHolder(VH holder, int section, int relativePosition,
      int absolutePosition, int adapterPosition);

  public void onBindViewHolder(VH holder, int section, int relativePosition, int absolutePosition,
      int adapterPosition, List<Object> payload) {
    onBindViewHolder(holder, section, relativePosition, absolutePosition, adapterPosition);
  }

  public final boolean isHeader(int position) {
    return mHeaderLocationMap.get(position) != null;
  }

  public final void setLayoutManager(@Nullable GridLayoutManager lm) {
    mLayoutManager = lm;
    if (lm == null) return;
    lm.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
      @Override public int getSpanSize(int position) {
        if (isHeader(position)) return mLayoutManager.getSpanCount();
        return 1;
      }
    });
  }

  // returns section along with offsetted position
  public int[] getSectionIndexAndRelativePosition(int itemPosition) {
    synchronized (mHeaderLocationMap) {
      Integer lastSectionIndex = -1;
      for (final Integer sectionIndex : mHeaderLocationMap.keySet()) {
        if (itemPosition > sectionIndex) {
          lastSectionIndex = sectionIndex;
        } else {
          break;
        }
        lastSectionIndex = sectionIndex;
      }
      return new int[] {
          mHeaderLocationMap.get(lastSectionIndex), itemPosition - lastSectionIndex - 1
      };
    }
  }

  @Override public final int getItemCount() {
    int count = 0;
    mHeaderLocationMap.clear();
    for (int s = 0; s < getSectionCount(); s++) {
      mHeaderLocationMap.put(count, s);
      count += getItemCount(s) + 1;
    }
    return count;
  }

  /**
   * @hide
   * @deprecated
   */
  @Override @Deprecated public final VH onCreateViewHolder(ViewGroup parent, int viewType) {
    return onCreateViewHolder(parent, viewType == VIEW_TYPE_HEADER);
  }

  /**
   * @hide
   * @deprecated
   */
  @Deprecated @Override public final int getItemViewType(int position) {
    if (isHeader(position)) {
      return VIEW_TYPE_HEADER;
    } else {
      return VIEW_TYPE_ITEM;
    }
  }

  /**
   * @hide
   * @deprecated
   */
  @Override @Deprecated public final void onBindViewHolder(VH holder, int position) {
    //Not implemented.
  }

  /**
   * @hide
   * @deprecated
   */
  @Deprecated @Override public final void onBindViewHolder(VH holder, int position,
      List<Object> payloads) {
    StaggeredGridLayoutManager.LayoutParams layoutParams = null;
    if (holder.itemView.getLayoutParams() instanceof GridLayoutManager.LayoutParams) {
      layoutParams =
          new StaggeredGridLayoutManager.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
              ViewGroup.LayoutParams.MATCH_PARENT);
    } else if (holder.itemView.getLayoutParams() instanceof StaggeredGridLayoutManager.LayoutParams) {
      layoutParams = (StaggeredGridLayoutManager.LayoutParams) holder.itemView.getLayoutParams();
    }
    if (isHeader(position)) {
      if (layoutParams != null) layoutParams.setFullSpan(true);
      onBindHeaderViewHolder(holder, mHeaderLocationMap.get(position), payloads);
    } else {
      if (layoutParams != null) layoutParams.setFullSpan(false);
      final int[] sectionAndPos = getSectionIndexAndRelativePosition(position);
      onBindViewHolder(holder, sectionAndPos[0],
          // offset section view positions
          sectionAndPos[1], position - (sectionAndPos[0] + 1), position, payloads);
    }
    if (layoutParams != null) holder.itemView.setLayoutParams(layoutParams);
  }
}