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);
		}
	}
}

Your ForwardingDataSetObserver is buggy: you should not forward positionStart "as is" to MergeAdapter. You should somewhat offset that value before to reflect the real position.

That depends, if clients are using getAdapterPosition() while getting positions within their viewholders, the correct non offseted value would be sent to the ForwardingDataSetObserver

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