HeaderViewRecyclerAdapter.java

package com.hotbitmapgg.moequest.adapter.helper;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.view.ViewGroup;

/**
 * RecycleView添加头部
 */
public class HeaderViewRecyclerAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

  private static final int HEADERS_START = Integer.MIN_VALUE;

  private static final int FOOTERS_START = Integer.MIN_VALUE + 10;

  private static final int ITEMS_START = Integer.MIN_VALUE + 20;

  private static final int ADAPTER_MAX_TYPES = 100;

  private RecyclerView.Adapter mWrappedAdapter;

  private List<View> mHeaderViews, mFooterViews;

  private Map<Class, Integer> mItemTypesOffset;


  public HeaderViewRecyclerAdapter(RecyclerView.Adapter adapter) {

    mHeaderViews = new ArrayList<>();
    mFooterViews = new ArrayList<>();
    mItemTypesOffset = new HashMap<>();
    setWrappedAdapter(adapter);
  }


  public void setAdapter(RecyclerView.Adapter adapter) {

    if (mWrappedAdapter != null && mWrappedAdapter.getItemCount() > 0) {
      notifyItemRangeRemoved(getHeaderCount(), mWrappedAdapter.getItemCount());
    }
    setWrappedAdapter(adapter);
    notifyItemRangeInserted(getHeaderCount(), mWrappedAdapter.getItemCount());
  }


  @Override
  public int getItemViewType(int position) {

    int hCount = getHeaderCount();
    if (position < hCount) {
      return HEADERS_START + position;
    } else {
      int itemCount = mWrappedAdapter.getItemCount();
      if (position < hCount + itemCount) {
        return getAdapterTypeOffset() + mWrappedAdapter.getItemViewType(position - hCount);
      } else {
        return FOOTERS_START + position - hCount - itemCount;
      }
    }
  }


  @Override
  public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {

    if (viewType < HEADERS_START + getHeaderCount()) {
      return new StaticViewHolder(mHeaderViews.get(viewType - HEADERS_START));
    } else if (viewType < FOOTERS_START + getFooterCount()) {
      return new StaticViewHolder(mFooterViews.get(viewType - FOOTERS_START));
    } else {
      return mWrappedAdapter.onCreateViewHolder(viewGroup, viewType - getAdapterTypeOffset());
    }
  }


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

    int hCount = getHeaderCount();
    if (position >= hCount && position < hCount + mWrappedAdapter.getItemCount()) {
      mWrappedAdapter.onBindViewHolder(viewHolder, position - hCount);
    }
  }


  public void addHeaderView(View view) {

    mHeaderViews.add(view);
  }


  public void addFooterView(View view) {

    mFooterViews.add(view);
  }


  @Override
  public int getItemCount() {

    return getHeaderCount() + getFooterCount() + getWrappedItemCount();
  }


  public int getWrappedItemCount() {

    return mWrappedAdapter.getItemCount();
  }


  public int getHeaderCount() {

    return mHeaderViews.size();
  }


  public int getFooterCount() {

    return mFooterViews.size();
  }


  private void setWrappedAdapter(RecyclerView.Adapter adapter) {

    if (mWrappedAdapter != null) mWrappedAdapter.unregisterAdapterDataObserver(mDataObserver);
    mWrappedAdapter = adapter;
    Class adapterClass = mWrappedAdapter.getClass();
    if (!mItemTypesOffset.containsKey(adapterClass)) putAdapterTypeOffset(adapterClass);
    mWrappedAdapter.registerAdapterDataObserver(mDataObserver);
  }


  private void putAdapterTypeOffset(Class adapterClass) {

    mItemTypesOffset.put(adapterClass, ITEMS_START + mItemTypesOffset.size() * ADAPTER_MAX_TYPES);
  }


  private int getAdapterTypeOffset() {

    return mItemTypesOffset.get(mWrappedAdapter.getClass());
  }


  private RecyclerView.AdapterDataObserver mDataObserver = new RecyclerView.AdapterDataObserver() {

    @Override
    public void onChanged() {

      super.onChanged();
      notifyDataSetChanged();
    }


    @Override
    public void onItemRangeChanged(int positionStart, int itemCount) {

      super.onItemRangeChanged(positionStart, itemCount);
      notifyItemRangeChanged(positionStart + getHeaderCount(), itemCount);
    }


    @Override
    public void onItemRangeInserted(int positionStart, int itemCount) {

      super.onItemRangeInserted(positionStart, itemCount);
      notifyItemRangeInserted(positionStart + getHeaderCount(), itemCount);
    }


    @Override
    public void onItemRangeRemoved(int positionStart, int itemCount) {

      super.onItemRangeRemoved(positionStart, itemCount);
      notifyItemRangeRemoved(positionStart + getHeaderCount(), itemCount);
    }


    @Override
    public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {

      super.onItemRangeMoved(fromPosition, toPosition, itemCount);
      int hCount = getHeaderCount();
      // TODO: No notifyItemRangeMoved method?
      notifyItemRangeChanged(fromPosition + hCount, toPosition + hCount + itemCount);
    }
  };

  private static class StaticViewHolder extends RecyclerView.ViewHolder {

    public StaticViewHolder(View itemView) {

      super(itemView);
    }
  }
}