Helper class to reproduce ListView's modal MultiChoice mode with a RecyclerView. Compatible with API 7+.

MultiChoiceHelper.java

package be.digitalia.common.widgets;

import android.content.Context;
import android.os.Build;
import android.os.Parcel;
import android.os.Parcelable;
import android.support.annotation.NonNull;
import android.support.v4.util.LongSparseArray;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.view.ActionMode;
import android.support.v7.widget.RecyclerView;
import android.util.SparseBooleanArray;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Checkable;

/**
 * Helper class to reproduce ListView's modal MultiChoice mode with a RecyclerView.
 * Compatible with API 7+.
 * Declare and use this class from inside your Adapter.
 *
 * @author Christophe Beyls
 */
public class MultiChoiceHelper {

	/**
	 * A handy ViewHolder base class which works with the MultiChoiceHelper
	 * and reproduces the default behavior of a ListView.
	 */
	public static abstract class ViewHolder extends RecyclerView.ViewHolder {

		View.OnClickListener clickListener;
		MultiChoiceHelper multiChoiceHelper;

		public ViewHolder(View itemView) {
			super(itemView);
			itemView.setOnClickListener(new View.OnClickListener() {
				@Override
				public void onClick(View view) {
					if (isMultiChoiceActive()) {
						int position = getAdapterPosition();
						if (position != RecyclerView.NO_POSITION) {
							multiChoiceHelper.toggleItemChecked(position, false);
							updateCheckedState(position);
						}
					} else {
						if (clickListener != null) {
							clickListener.onClick(view);
						}
					}
				}
			});
			itemView.setOnLongClickListener(new View.OnLongClickListener() {
				@Override
				public boolean onLongClick(View view) {
					if ((multiChoiceHelper == null) || isMultiChoiceActive()) {
						return false;
					}
					int position = getAdapterPosition();
					if (position != RecyclerView.NO_POSITION) {
						multiChoiceHelper.setItemChecked(position, true, false);
						updateCheckedState(position);
					}
					return true;
				}
			});
		}

		void updateCheckedState(int position) {
			final boolean isChecked = multiChoiceHelper.isItemChecked(position);
			if (itemView instanceof Checkable) {
				((Checkable) itemView).setChecked(isChecked);
			} else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
				itemView.setActivated(isChecked);
			}
		}

		public void setOnClickListener(View.OnClickListener clickListener) {
			this.clickListener = clickListener;
		}

		public void bind(MultiChoiceHelper multiChoiceHelper, int position) {
			this.multiChoiceHelper = multiChoiceHelper;
			if (multiChoiceHelper != null) {
				updateCheckedState(position);
			}
		}

		public boolean isMultiChoiceActive() {
			return (multiChoiceHelper != null) && (multiChoiceHelper.getCheckedItemCount() > 0);
		}
	}

	public interface MultiChoiceModeListener extends ActionMode.Callback {
		/**
		 * Called when an item is checked or unchecked during selection mode.
		 *
		 * @param mode     The {@link ActionMode} providing the selection startSupportActionModemode
		 * @param position Adapter position of the item that was checked or unchecked
		 * @param id       Adapter ID of the item that was checked or unchecked
		 * @param checked  <code>true</code> if the item is now checked, <code>false</code>
		 *                 if the item is now unchecked.
		 */
		void onItemCheckedStateChanged(ActionMode mode, int position, long id, boolean checked);
	}

	private static final int CHECK_POSITION_SEARCH_DISTANCE = 20;

	private final AppCompatActivity activity;
	private final RecyclerView.Adapter adapter;
	private SparseBooleanArray checkStates;
	private LongSparseArray<Integer> checkedIdStates;
	private int checkedItemCount = 0;
	private MultiChoiceModeWrapper multiChoiceModeCallback;
	ActionMode choiceActionMode;

	/**
	 * Make sure this constructor is called before setting the adapter on the RecyclerView
	 * so this class will be notified before the RecyclerView in case of data set changes.
	 */
	public MultiChoiceHelper(@NonNull AppCompatActivity activity, @NonNull RecyclerView.Adapter adapter) {
		this.activity = activity;
		this.adapter = adapter;
		adapter.registerAdapterDataObserver(new AdapterDataSetObserver());
		checkStates = new SparseBooleanArray(0);
		if (adapter.hasStableIds()) {
			checkedIdStates = new LongSparseArray<>(0);
		}
	}

	public Context getContext() {
		return activity;
	}

	public void setMultiChoiceModeListener(MultiChoiceModeListener listener) {
		if (listener == null) {
			multiChoiceModeCallback = null;
			return;
		}
		if (multiChoiceModeCallback == null) {
			multiChoiceModeCallback = new MultiChoiceModeWrapper();
		}
		multiChoiceModeCallback.setWrapped(listener);
	}

	public int getCheckedItemCount() {
		return checkedItemCount;
	}

	public boolean isItemChecked(int position) {
		return checkStates.get(position);
	}

	public SparseBooleanArray getCheckedItemPositions() {
		return checkStates;
	}

	public long[] getCheckedItemIds() {
		final LongSparseArray<Integer> idStates = checkedIdStates;
		if (idStates == null) {
			return new long[0];
		}

		final int count = idStates.size();
		final long[] ids = new long[count];

		for (int i = 0; i < count; i++) {
			ids[i] = idStates.keyAt(i);
		}

		return ids;
	}

	public void clearChoices() {
		if (checkedItemCount > 0) {
			final int start = checkStates.keyAt(0);
			final int end = checkStates.keyAt(checkStates.size() - 1);
			checkStates.clear();
			if (checkedIdStates != null) {
				checkedIdStates.clear();
			}
			checkedItemCount = 0;

			adapter.notifyItemRangeChanged(start, end - start + 1);

			if (choiceActionMode != null) {
				choiceActionMode.finish();
			}
		}
	}

	public void setItemChecked(int position, boolean value, boolean notifyChanged) {
		// Start selection mode if needed. We don't need to if we're unchecking something.
		if (value) {
			startSupportActionModeIfNeeded();
		}

		boolean oldValue = checkStates.get(position);
		checkStates.put(position, value);

		if (oldValue != value) {
			final long id = adapter.getItemId(position);

			if (checkedIdStates != null) {
				if (value) {
					checkedIdStates.put(id, position);
				} else {
					checkedIdStates.delete(id);
				}
			}

			if (value) {
				checkedItemCount++;
			} else {
				checkedItemCount--;
			}

			if (notifyChanged) {
				adapter.notifyItemChanged(position);
			}

			if (choiceActionMode != null) {
				multiChoiceModeCallback.onItemCheckedStateChanged(choiceActionMode, position, id, value);
				if (checkedItemCount == 0) {
					choiceActionMode.finish();
				}
			}
		}
	}

	public void toggleItemChecked(int position, boolean notifyChanged) {
		setItemChecked(position, !isItemChecked(position), notifyChanged);
	}

	public Parcelable onSaveInstanceState() {
		SavedState savedState = new SavedState();
		savedState.checkedItemCount = checkedItemCount;
		savedState.checkStates = clone(checkStates);
		if (checkedIdStates != null) {
			savedState.checkedIdStates = checkedIdStates.clone();
		}
		return savedState;
	}

	private static SparseBooleanArray clone(SparseBooleanArray original) {
		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
			return original.clone();
		}
		final int size = original.size();
		SparseBooleanArray clone = new SparseBooleanArray(size);
		for (int i = 0; i < size; ++i) {
			clone.append(original.keyAt(i), original.valueAt(i));
		}
		return clone;
	}

	public void onRestoreInstanceState(Parcelable state) {
		if ((state != null) && (checkedItemCount == 0)) {
			SavedState savedState = (SavedState) state;
			checkedItemCount = savedState.checkedItemCount;
			checkStates = savedState.checkStates;
			checkedIdStates = savedState.checkedIdStates;

			if (checkedItemCount > 0) {
				// Empty adapter is given a chance to be populated before completeRestoreInstanceState()
				if (adapter.getItemCount() > 0) {
					confirmCheckedPositions();
				}
				activity.getWindow().getDecorView().post(new Runnable() {
					@Override
					public void run() {
						completeRestoreInstanceState();
					}
				});
			}
		}
	}

	void completeRestoreInstanceState() {
		if (checkedItemCount > 0) {
			if (adapter.getItemCount() == 0) {
				// Adapter was not populated, clear the selection
				confirmCheckedPositions();
			} else {
				startSupportActionModeIfNeeded();
			}
		}
	}

	private void startSupportActionModeIfNeeded() {
		if (choiceActionMode == null) {
			if (multiChoiceModeCallback == null) {
				throw new IllegalStateException("No callback set");
			}
			choiceActionMode = activity.startSupportActionMode(multiChoiceModeCallback);
		}
	}

	public static class SavedState implements Parcelable {

		int checkedItemCount;
		SparseBooleanArray checkStates;
		LongSparseArray<Integer> checkedIdStates;

		SavedState() {
		}

		SavedState(Parcel in) {
			checkedItemCount = in.readInt();
			checkStates = in.readSparseBooleanArray();
			final int n = in.readInt();
			if (n >= 0) {
				checkedIdStates = new LongSparseArray<>(n);
				for (int i = 0; i < n; i++) {
					final long key = in.readLong();
					final int value = in.readInt();
					checkedIdStates.append(key, value);
				}
			}
		}

		@Override
		public void writeToParcel(Parcel out, int flags) {
			out.writeInt(checkedItemCount);
			out.writeSparseBooleanArray(checkStates);
			final int n = checkedIdStates != null ? checkedIdStates.size() : -1;
			out.writeInt(n);
			for (int i = 0; i < n; i++) {
				out.writeLong(checkedIdStates.keyAt(i));
				out.writeInt(checkedIdStates.valueAt(i));
			}
		}

		@Override
		public int describeContents() {
			return 0;
		}

		public static final Creator<SavedState> CREATOR = new Creator<SavedState>() {
			@Override
			public SavedState createFromParcel(Parcel in) {
				return new SavedState(in);
			}

			@Override
			public SavedState[] newArray(int size) {
				return new SavedState[size];
			}
		};
	}

	void confirmCheckedPositions() {
		if (checkedItemCount == 0) {
			return;
		}

		final int itemCount = adapter.getItemCount();
		boolean checkedCountChanged = false;

		if (itemCount == 0) {
			// Optimized path for empty adapter: remove all items.
			checkStates.clear();
			if (checkedIdStates != null) {
				checkedIdStates.clear();
			}
			checkedItemCount = 0;
			checkedCountChanged = true;
		} else if (checkedIdStates != null) {
			// Clear out the positional check states, we'll rebuild it below from IDs.
			checkStates.clear();

			for (int checkedIndex = 0; checkedIndex < checkedIdStates.size(); checkedIndex++) {
				final long id = checkedIdStates.keyAt(checkedIndex);
				final int lastPos = checkedIdStates.valueAt(checkedIndex);

				if ((lastPos >= itemCount) || (id != adapter.getItemId(lastPos))) {
					// Look around to see if the ID is nearby. If not, uncheck it.
					final int start = Math.max(0, lastPos - CHECK_POSITION_SEARCH_DISTANCE);
					final int end = Math.min(lastPos + CHECK_POSITION_SEARCH_DISTANCE, itemCount);
					boolean found = false;
					for (int searchPos = start; searchPos < end; searchPos++) {
						final long searchId = adapter.getItemId(searchPos);
						if (id == searchId) {
							found = true;
							checkStates.put(searchPos, true);
							checkedIdStates.setValueAt(checkedIndex, searchPos);
							break;
						}
					}

					if (!found) {
						checkedIdStates.delete(id);
						checkedIndex--;
						checkedItemCount--;
						checkedCountChanged = true;
						if (choiceActionMode != null && multiChoiceModeCallback != null) {
							multiChoiceModeCallback.onItemCheckedStateChanged(choiceActionMode, lastPos, id, false);
						}
					}
				} else {
					checkStates.put(lastPos, true);
				}
			}
		} else {
			// If the total number of items decreased, remove all out-of-range check indexes.
			for (int i = checkStates.size() - 1; (i >= 0) && (checkStates.keyAt(i) >= itemCount); i--) {
				if (checkStates.valueAt(i)) {
					checkedItemCount--;
					checkedCountChanged = true;
				}
				checkStates.delete(checkStates.keyAt(i));
			}
		}

		if (checkedCountChanged && choiceActionMode != null) {
			if (checkedItemCount == 0) {
				choiceActionMode.finish();
			} else {
				choiceActionMode.invalidate();
			}
		}
	}

	class AdapterDataSetObserver extends RecyclerView.AdapterDataObserver {

		@Override
		public void onChanged() {
			confirmCheckedPositions();
		}

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

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

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

	class MultiChoiceModeWrapper implements MultiChoiceModeListener {

		private MultiChoiceModeListener wrapped;

		public void setWrapped(@NonNull MultiChoiceModeListener wrapped) {
			this.wrapped = wrapped;
		}

		@Override
		public boolean onCreateActionMode(ActionMode mode, Menu menu) {
			return wrapped.onCreateActionMode(mode, menu);
		}

		@Override
		public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
			return wrapped.onPrepareActionMode(mode, menu);
		}

		@Override
		public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
			return wrapped.onActionItemClicked(mode, item);
		}

		@Override
		public void onDestroyActionMode(ActionMode mode) {
			wrapped.onDestroyActionMode(mode);
			choiceActionMode = null;
			clearChoices();
		}

		@Override
		public void onItemCheckedStateChanged(ActionMode mode, int position, long id, boolean checked) {
			wrapped.onItemCheckedStateChanged(mode, position, id, checked);
		}
	}
}