A Merge Adapter for the RecyclerView. Based on CommonsWare cwac-merge and the MergedAdapter in the android sdk.

MergeRecyclerAdapter

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

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

/**
 * The MergeRecyclerAdapter is inspired by the cwac-merge adapter, but for
 * the RecyclerView.
 *
 * This adapter essentially merges a collection of adapters/views into one adapter.
 *
 * Methods are provided for adding single views or a list of views, but under the hood
 * these views are then put into an adapter themselves, even if the adapter only holds the
 * one view.
 *
 * RecyclerView Adapters must implement both the {@link android.support.v7.widget.RecyclerView.Adapter#onCreateViewHolder(android.view
 * .ViewGroup, int)}
 * and {@link android.support.v7.widget.RecyclerView.Adapter#onBindViewHolder(android.support.v7.widget.RecyclerView.ViewHolder,
 * int)} methods, as opposed to just the {@link android.widget.BaseAdapter#getView(int, android.view.View,
 * android.view.ViewGroup)} method in a ListView Adapter.
 *
 * Because the {@link android.support.v7.widget.RecyclerView.Adapter#onCreateViewHolder(android.view
 * .ViewGroup, int)} method only provides us the ViewGroup and a View Type, we must keep a mapping of
 * (unique) view types in this merge adapter to each sub adapter, so we know which adapters' onCreateViewHolder method to call.
 *
 * The {@link MergeRecyclerAdapter.LocalAdapter} class
 * is used to maintain this mapping, and the {@link mViewTypeIndex} field is used to provide a unique
 * view type.
 *
 *
 * -------------
 * BUGS
 * -------------
 *
 * There currently exists a bug when merging Views and Adapters. The RecyclerView throws the following error:
 *
 java.lang.IllegalArgumentException: Scrapped or attached views may not be recycled.
 at android.support.v7.widget.RecyclerView$Recycler.recycleViewHolder(RecyclerView.java:2569)
 at android.support.v7.widget.RecyclerView$Recycler.quickRecycleScrapView(RecyclerView.java:2610)
 at android.support.v7.widget.RecyclerView$LayoutManager.removeAndRecycleScrapInt(RecyclerView.java:3992)
 at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:1533)
 at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:1600)
 at android.view.View.layout(View.java:15273)


 *
 *  I currently don't know what the fix is for this issue.
 *
 */
public class MergeRecyclerAdapter<T extends RecyclerView.Adapter> extends RecyclerView
		.Adapter {

	private Context mContext;
	protected ArrayList<LocalAdapter> mAdapters = new ArrayList<>();
	protected ForwardingDataSetObserver observer = new ForwardingDataSetObserver();
	private int mViewTypeIndex=0;

	public MergeRecyclerAdapter() {
	}

	public MergeRecyclerAdapter(Context context) {
		this.mContext = context;
	}

	/**
	 * A Mergeable adapter must implement both ListAdapter and SpinnerAdapter to be useful in lists and spinners.
	 */

	public class LocalAdapter {
		public final T mAdapter;
		public int mLocalPosition = 0;
		public Map<Integer, Integer> mViewTypesMap = new HashMap<>();

		public LocalAdapter(T adapter) {
			mAdapter = adapter;
		}
	}

	/** Append the given adapter to the list of merged adapters. */
	public void addAdapter(T adapter) {
		addAdapter(mAdapters.size(), adapter);
	}

	/** Add the given adapter to the list of merged adapters at the given index. */
	public void addAdapter(int index, T adapter) {
		mAdapters.add(index, new LocalAdapter(adapter));
		adapter.registerAdapterDataObserver(observer);
		notifyDataSetChanged();
	}

	/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
	 * remove adapter
	 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

	/** Remove the given adapter from the list of merged adapters. */
	public void removeAdapter(T adapter) {
		if (!mAdapters.contains(adapter)) return;
		removeAdapter(mAdapters.indexOf(adapter));
	}

	/** Remove the adapter at the given index from the list of merged adapters. */
	public void removeAdapter(int index) {
		if (index < 0 || index >= mAdapters.size()) return;
		LocalAdapter adapter = mAdapters.remove(index);
		adapter.mAdapter.unregisterAdapterDataObserver(observer);
		notifyDataSetChanged();
	}

	public int getSubAdapterCount() {
		return mAdapters.size();
	}

	public T getSubAdapter(int index) {
		return mAdapters.get(index).mAdapter;
	}

	/**
	 * Adds a new View to the roster of things to appear in
	 * the aggregate list.
	 *
	 * @param view
	 *          Single view to add
	 * @param enabled
	 *          false if views are disabled, true if enabled
	 */
	public void addView(View view) {
		ArrayList<View> list=new ArrayList<View>(1);

		list.add(view);

		addViews(list);
	}

	/**
	 * Adds a list of views to the roster of things to appear
	 * in the aggregate list.
	 *
	 * @param views
	 *          List of views to add
	 */
	public void addViews(List<View> views) {
		addAdapter((T) new ViewsAdapter(mContext,views));
	}

	@Override public int getItemCount() {
		int count = 0;
		for (LocalAdapter adapter : mAdapters) {
			count += adapter.mAdapter.getItemCount();
		}
		return count;
		// TODO: cache counts until next onChanged
	}

	/**
	 * For a given merged position, find the corresponding Adapter and local position within that Adapter by iterating through Adapters and
	 * summing their counts until the merged position is found.
	 *
	 * @param position a merged (global) position
	 * @return the matching Adapter and local position, or null if not found
	 */
	public LocalAdapter getAdapterOffsetForItem(final int position) {
		final int adapterCount = mAdapters.size();
		int i = 0;
		int count = 0;

		while (i < adapterCount) {
			LocalAdapter a = mAdapters.get(i);
			int newCount = count + a.mAdapter.getItemCount();
			if (position < newCount) {
				a.mLocalPosition = position - count;
				return a;
			}
			count = newCount;
			i++;
		}
		return null;
	}

	@Override public long getItemId(int position) {
		return position;
	}


	@Override public int getItemViewType(int position) {
		LocalAdapter result = getAdapterOffsetForItem(position);
		int localViewType = result.mAdapter.getItemViewType(result.mLocalPosition);
		if (result.mViewTypesMap.containsValue(localViewType)) {
			for (Map.Entry<Integer, Integer> entry : result.mViewTypesMap.entrySet()) {
				if (entry.getValue() == localViewType) {
					return entry.getKey();
				}
			}
		}
		mViewTypeIndex += 1;
		result.mViewTypesMap.put(mViewTypeIndex, localViewType);
		return mViewTypeIndex;
	}


	@Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
		for (LocalAdapter adapter: mAdapters){
			if (adapter.mViewTypesMap.containsKey(viewType))
				return adapter.mAdapter.onCreateViewHolder(viewGroup,adapter.mViewTypesMap.get(viewType));
		}
		return null;
	}

	@Override public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
		LocalAdapter result = getAdapterOffsetForItem(position);
		result.mAdapter.onBindViewHolder(viewHolder, result.mLocalPosition);
	}

	/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
	 * forwarding data set observer
	 * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

	private class ForwardingDataSetObserver extends RecyclerView.AdapterDataObserver {
		@Override public void onChanged() {
			notifyDataSetChanged();
		}

		@Override public void onItemRangeChanged(int positionStart, int itemCount) {
			super.onItemRangeChanged(positionStart, itemCount);
			notifyItemRangeChanged(positionStart, itemCount);
		}

		@Override public void onItemRangeInserted(int positionStart, int itemCount) {
			super.onItemRangeInserted(positionStart, itemCount);
			notifyItemRangeInserted(positionStart, itemCount);
		}

		@Override public void onItemRangeRemoved(int positionStart, int itemCount) {
			super.onItemRangeRemoved(positionStart, itemCount);
			notifyItemRangeRemoved(positionStart, itemCount);
		}
	}


	/**
	 * ViewsAdapter, ported from CommonsWare SackOfViews adapter.
	 */
	public static class ViewsAdapter extends RecyclerView.Adapter {
		private List<View> views=null;
		private Context context;

		/**
		 * Constructor creating an empty list of views, but with
		 * a specified count. Subclasses must override newView().
		 */
		public ViewsAdapter(Context context, int count) {
			super();
			this.context = context;

			views=new ArrayList<>(count);

			for (int i=0;i<count;i++) {
				views.add(null);
			}
		}

		/**
		 * Constructor wrapping a supplied list of views.
		 * Subclasses must override newView() if any of the elements
		 * in the list are null.
		 */
		public ViewsAdapter(Context context, List<View> views) {
			super();
			this.context = context;

			this.views=views;
		}

		/**
		 * How many items are in the data set represented by this
		 * Adapter.
		 */
		@Override
		public int getItemCount() {
			return(views.size());
		}

		/**
		 * Get the type of View that will be created by getView()
		 * for the specified item.
		 * @param position Position of the item whose data we want
		 */
		@Override
		public int getItemViewType(int position) {
			return(position);
		}

		@Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
			//view type is equal to the position in this adapter.
			ViewsViewHolder holder = new ViewsViewHolder(views.get(viewType));
			return holder;
		}

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

		/**
		 * Get the row id associated with the specified position
		 * in the list.
		 * @param position Position of the item whose data we want
		 */
		@Override
		public long getItemId(int position) {
			return(position);
		}

		public boolean hasView(View v) {
			return(views.contains(v));
		}

		/**
		 * Create a new View to go into the list at the specified
		 * position.
		 * @param position Position of the item whose data we want
		 * @param parent ViewGroup containing the returned View
		 */
		protected View newView(int position, ViewGroup parent) {
			throw new RuntimeException("You must override newView()!");
		}
	}

	public static class ViewsViewHolder extends RecyclerView.ViewHolder{
		public ViewsViewHolder(View itemView) {
			super(itemView);
		}
	}
}

I want to know license of this code. CC0, APACHE2 or MIT?

Licensed under Apache Software License 2.0.

I implemented something similar recently.
You need to shift positions in the datasetobserver because the sub-adapter only knows its own adapter positions. In addition, you should provide a utility method to return the real adapter position from the ViewHolder, to be called in place of ViewHolder.getAdapterPosition()

Thank you for your good gist.
I forked and included this in my library https://github.com/cattaka/AdapterToolbox