RecyclerView adapter designed to wrap an existing adapter allowing the addition of header views and footer views.

HeaderViewRecyclerAdapter.java

/*
 * Copyright (C) 2014 darnmason
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

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

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

/**
 * <p>
 * RecyclerView adapter designed to wrap an existing adapter allowing the addition of
 * header views and footer views.
 * </p>
 * <p>
 * I implemented it to aid with the transition from ListView to RecyclerView where the ListView's
 * addHeaderView and addFooterView methods were used. Using this class you may initialize your
 * header views in the Fragment/Activity and add them to the adapter in the same way you used to
 * add them to a ListView.
 * </p>
 * <p>
 * I also required to be able to swap out multiple adapters with different content, therefore
 * setAdapter may be called multiple times.
 * </p>
 * Created by darnmason on 07/11/2014.
 */
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;

    /**
     * Construct a new header view recycler adapter
     * @param adapter The underlying adapter to wrap
     */
    public HeaderViewRecyclerAdapter(RecyclerView.Adapter adapter) {
        mHeaderViews = new ArrayList<View>();
        mFooterViews = new ArrayList<View>();
        mItemTypesOffset = new HashMap<Class, Integer>();
        setWrappedAdapter(adapter);
    }

    /**
     * Replaces the underlying adapter, notifying RecyclerView of changes
     * @param adapter The new adapter to wrap
     */
    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);
    }

    /**
     * Add a static view to appear at the start of the RecyclerView. Headers are displayed in the
     * order they were added.
     * @param view The header view to add
     */
    public void addHeaderView(View view) {
        mHeaderViews.add(view);
    }

    /**
     * Add a static view to appear at the end of the RecyclerView. Footers are displayed in the
     * order they were added.
     * @param view The footer view to add
     */
    public void addFooterView(View view) {
        mFooterViews.add(view);
    }

    @Override
    public int getItemCount() {
        return getHeaderCount() + getFooterCount() + getWrappedItemCount();
    }

    /**
     * @return The item count in the underlying adapter
     */
    public int getWrappedItemCount() {
        return mWrappedAdapter.getItemCount();
    }

    /**
     * @return The number of header views added
     */
    public int getHeaderCount() {
        return mHeaderViews.size();
    }

    /**
     * @return The number of footer views added
     */
    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);
        }
    }
}

when I try to remove a added footer/head, app crashes with the exception of "java.lang.IndexOutOfBoundsException: Inconsistency detected. Invalid view holder adapter positionViewHolder{52e4493c position=2 id=-1, oldPos=1, pLpos:1 scrap tmpDetached no parent}", and I googled ,but got nothing.Can you help me out?

Sorry I didn't get a notification about this comment. I didn't deal with removing headers/footers as I tried to avoid that practice when using ListView. Instead I would show/hide headers and footers as required.

However, in your case it sounds like you are not notifying changes appropriately. What I would do is determine the index of the view being removed, which is simple for headers and depends on the size of the wrapped adapter for footers, and call notifyItemRemoved(index) after removing the view.

There is a problem in the drag and drop functionality.

1. HeaderView also drag and drop. This should not be done
2. crash occured index out of bound exception

Can you help me out in this?

fix cast exception when user override onViewAttachedToWindow or onViewDetachedFromWindow method
wish do someone's help

  @Override public void onViewAttachedToWindow(RecyclerView.ViewHolder holder) {
    final boolean isHeadOrFootView = isHeadOrFootView(holder);
    if (isHeadOrFootView) {
      super.onViewAttachedToWindow(holder);
    } else {
      wrappedAdapter.onViewAttachedToWindow(holder);
    }
  }

  @Override public void onViewDetachedFromWindow(RecyclerView.ViewHolder holder) {
    final boolean  isHeadOrFootView = isHeadOrFootView(holder);
    if (isHeadOrFootView) {
      super.onViewAttachedToWindow(holder);
    } else {
      wrappedAdapter.onViewDetachedFromWindow(holder);
    }
  }


  private boolean isHeadOrFootView(RecyclerView.ViewHolder holder) {
    return (holder instanceof StaticViewHolder);
  }