src/com/android/documentsui/selection/DefaultSelectionHelper.java - LeafOS-Project/android_packages_apps_DocumentsUI - Gitiles

 /*
  * Copyright (C) 2015 The Android Open Source Project
  *
  * 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.
  */

 package com.android.documentsui.selection;

 import static android.support.v4.util.Preconditions.checkArgument;
 import static android.support.v4.util.Preconditions.checkState;
 import static com.android.documentsui.selection.Shared.DEBUG;
 import static com.android.documentsui.selection.Shared.TAG;

 import android.support.annotation.IntDef;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.RecyclerView.Adapter;
 import android.util.Log;

 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;

 import javax.annotation.Nullable;

 /**
  * {@link SelectionHelper} providing support traditional multi-item selection on top
  * of {@link RecyclerView}.
  *
  * <p>The class supports running in a single-select mode, which can be enabled
  * by passing {@colde #MODE_SINGLE} to the constructor.
  */
 public final class DefaultSelectionHelper extends SelectionHelper {

     public static final int MODE_MULTIPLE = 0;
     public static final int MODE_SINGLE = 1;

     @IntDef(flag = true, value = {
             MODE_MULTIPLE,
             MODE_SINGLE
     })
     @Retention(RetentionPolicy.SOURCE)
     public @interface SelectionMode {}

     private static final int RANGE_REGULAR = 0;

     /**
      * "Provisional" selection represents a overlay on the primary selection. A provisional
      * selection maybe be eventually added to the primary selection, or it may be abandoned.
      *
      * <p>E.g. BandController creates a provisional selection while a user is actively selecting
      * items with the band. Provisionally selected items are considered to be selected in
      * {@link Selection#contains(String)} and related methods. A provisional may be abandoned or
      * applied by selection components (like
      * {@link com.android.documentsui.selection.BandSelectionHelper}).
      *
      * <p>A provisional selection may intersect the primary selection, however clearing the
      * provisional selection will not affect the primary selection where the two may intersect.
      */
     private static final int RANGE_PROVISIONAL = 1;
     @IntDef({
         RANGE_REGULAR,
         RANGE_PROVISIONAL
     })
     @Retention(RetentionPolicy.SOURCE)
     @interface RangeType {}

     private final Selection mSelection = new Selection();
     private final List<SelectionObserver> mObservers = new ArrayList<>(1);
     private final RecyclerView.Adapter<?> mAdapter;
     private final StableIdProvider mStableIds;
     private final SelectionPredicate mSelectionPredicate;
     private final RecyclerView.AdapterDataObserver mAdapterObserver;
     private final RangeCallbacks mRangeCallbacks;
     private final boolean mSingleSelect;

     private @Nullable Range mRange;

     /**
      * Creates a new instance.
      *
      * @param mode single or multiple selection mode. In single selection mode
      *     users can only select a single item.
      * @param adapter {@link Adapter} for the RecyclerView this instance is coupled with.
      * @param stableIds client supplied class providing access to stable ids.
      * @param selectionPredicate A predicate allowing the client to disallow selection
      *     of individual elements.
      */
     public DefaultSelectionHelper(
             @SelectionMode int mode,
             RecyclerView.Adapter<?> adapter,
             StableIdProvider stableIds,
             SelectionPredicate selectionPredicate) {

         checkArgument(mode == MODE_SINGLE || mode == MODE_MULTIPLE);
         checkArgument(adapter != null);
         checkArgument(stableIds != null);
         checkArgument(selectionPredicate != null);

         mAdapter = adapter;
         mStableIds = stableIds;
         mSelectionPredicate = selectionPredicate;
         mAdapterObserver = new AdapterObserver();
         mRangeCallbacks = new RangeCallbacks();

         mSingleSelect = mode == MODE_SINGLE;

         mAdapter.registerAdapterDataObserver(mAdapterObserver);
     }

     @Override
     public void addObserver(SelectionObserver callback) {
         checkArgument(callback != null);
         mObservers.add(callback);
     }

     @Override
     public boolean hasSelection() {
         return !mSelection.isEmpty();
     }

     @Override
     public Selection getSelection() {
         return mSelection;
     }

     @Override
     public void copySelection(Selection dest) {
         dest.copyFrom(mSelection);
     }

     @Override
     public boolean isSelected(String id) {
         return mSelection.contains(id);
     }

     @Override
     public void restoreSelection(Selection other) {
         setItemsSelectedQuietly(other.mSelection, true);
         // NOTE: We intentionally don't restore provisional selection. It's provisional.
         notifySelectionRestored();
     }

     @Override
     public boolean setItemsSelected(Iterable<String> ids, boolean selected) {
         boolean changed = setItemsSelectedQuietly(ids, selected);
         notifySelectionChanged();
         return changed;
     }

     private boolean setItemsSelectedQuietly(Iterable<String> ids, boolean selected) {
         boolean changed = false;
         for (String id: ids) {
             boolean itemChanged = selected
                     ? canSetState(id, true) && mSelection.add(id)
                     : canSetState(id, false) && mSelection.remove(id);
             if (itemChanged) {
                 notifyItemStateChanged(id, selected);
             }
             changed |= itemChanged;
         }
         return changed;
     }

     @Override
     public void clearSelection() {
         if (!hasSelection()) {
             return;
         }

         Selection prev = clearSelectionQuietly();
         notifySelectionCleared(prev);
         notifySelectionChanged();
     }

     /**
      * Clears the selection, without notifying selection listeners.
      * Returns items in previous selection. Callers are responsible for notifying
      * listeners about changes.
      */
     private Selection clearSelectionQuietly() {
         mRange = null;

         Selection prevSelection = new Selection();
         if (hasSelection()) {
             copySelection(prevSelection);
             mSelection.clear();
         }

         return prevSelection;
     }

     @Override
     public boolean select(String id) {
         checkArgument(id != null);

         if (!mSelection.contains(id)) {
             if (!canSetState(id, true)) {
                 if (DEBUG) Log.d(TAG, "Select cancelled by selection predicate test.");
                 return false;
             }

             // Enforce single selection policy.
             if (mSingleSelect && hasSelection()) {
                 Selection prev = clearSelectionQuietly();
                 notifySelectionCleared(prev);
             }

             mSelection.add(id);
             notifyItemStateChanged(id, true);
             notifySelectionChanged();

             return true;
         }

         return false;
     }

     @Override
     public boolean deselect(String id) {
         checkArgument(id != null);

         if (mSelection.contains(id)) {
             if (!canSetState(id, false)) {
                 if (DEBUG) Log.d(TAG, "Deselect cancelled by selection predicate test.");
                 return false;
             }
             mSelection.remove(id);
             notifyItemStateChanged(id, false);
             notifySelectionChanged();
             if (mSelection.isEmpty() && isRangeActive()) {
                 // if there's nothing in the selection and there is an active ranger it results
                 // in unexpected behavior when the user tries to start range selection: the item
                 // which the ranger 'thinks' is the already selected anchor becomes unselectable
                 endRange();
             }
             return true;
         }

         return false;
     }

     @Override
     public void startRange(int pos) {
         select(mStableIds.getStableId(pos));
         anchorRange(pos);
     }

     @Override
     public void extendRange(int pos) {
         extendRange(pos, RANGE_REGULAR);
     }

     @Override
     public void endRange() {
         mRange = null;
         // Clean up in case there was any leftover provisional selection
         clearProvisionalSelection();
     }

     @Override
     public void anchorRange(int position) {
         checkArgument(position != RecyclerView.NO_POSITION);

         // TODO: I'm not a fan of silently ignoring calls.
         // Determine if there are any cases where method can be called
         // w/o item already being selected. Else, tighten up the ship
         // and make this conditional guard into a proper precondition check.
         if (mSelection.contains(mStableIds.getStableId(position))) {
             mRange = new Range(mRangeCallbacks, position);
         }
     }

     @Override
     public void extendProvisionalRange(int pos) {
         extendRange(pos, RANGE_PROVISIONAL);
     }

     /**
      * Sets the end point for the current range selection, started by a call to
      * {@link #startRange(int)}. This function should only be called when a range selection
      * is active (see {@link #isRangeActive()}. Items in the range [anchor, end] will be
      * selected or in provisional select, depending on the type supplied. Note that if the type is
      * provisional selection, one should do {@link #mergeProvisionalSelection()} at some
      * point before calling on {@link #endRange()}.
      *
      * @param pos The new end position for the selection range.
      * @param type The type of selection the range should utilize.
      */
     private void extendRange(int pos, @RangeType int type) {
         checkState(isRangeActive(), "Range start point not set.");

         mRange.extendSelection(pos, type);

         // We're being lazy here notifying even when something might not have changed.
         // To make this more correct, we'd need to update the Ranger class to return
         // information about what has changed.
         notifySelectionChanged();
     }

     @Override
     public void setProvisionalSelection(Set<String> newSelection) {
         Map<String, Boolean> delta = mSelection.setProvisionalSelection(newSelection);
         for (Map.Entry<String, Boolean> entry: delta.entrySet()) {
             notifyItemStateChanged(entry.getKey(), entry.getValue());
         }

         notifySelectionChanged();
     }

     @Override
     public void mergeProvisionalSelection() {
         mSelection.mergeProvisionalSelection();
     }

     @Override
     public void clearProvisionalSelection() {
         for (String id : mSelection.mProvisionalSelection) {
             notifyItemStateChanged(id, false);
         }
         mSelection.clearProvisionalSelection();
     }

     @Override
     public boolean isRangeActive() {
         return mRange != null;
     }

     private boolean canSetState(String id, boolean nextState) {
         return mSelectionPredicate.canSetStateForId(id, nextState);
     }

     private void onDataSetChanged() {
         // Update the selection to remove any disappeared IDs.
         mSelection.clearProvisionalSelection();
         mSelection.intersect(mStableIds.getStableIds());
         notifySelectionReset();

         for (String id : mSelection) {
             // If the underlying data set has changed, before restoring
             // selection we must re-verify that it can be selected.
             // Why? Because if the dataset has changed, then maybe the
             // selectability of an item has changed.
             if (!canSetState(id, true)) {
                 deselect(id);
             } else {
                 int lastListener = mObservers.size() - 1;
                 for (int i = lastListener; i >= 0; i--) {
                     mObservers.get(i).onItemStateChanged(id, true);
                 }
             }
         }
         notifySelectionChanged();
     }

     private void onDataSetItemRangeInserted(int startPosition, int itemCount) {
         mSelection.clearProvisionalSelection();
     }

     private void onDataSetItemRangeRemoved(int startPosition, int itemCount) {
         checkArgument(startPosition >= 0);
         checkArgument(itemCount > 0);

         mSelection.clearProvisionalSelection();

         // Remove any disappeared IDs from the selection.
         //
         // Ideally there could be a cheaper approach, checking
         // each position individually, but since the source of
         // truth for stable ids (StableIdProvider) probably
         // it-self no-longer knows about the positions in question
         // we fall back to the sledge hammer approach.
         mSelection.intersect(mStableIds.getStableIds());
     }

     /**
      * Notifies registered listeners when the selection status of a single item
      * (identified by {@code position}) changes.
      */
     private void notifyItemStateChanged(String id, boolean selected) {
         checkArgument(id != null);

         int lastListenerIndex = mObservers.size() - 1;
         for (int i = lastListenerIndex; i >= 0; i--) {
             mObservers.get(i).onItemStateChanged(id, selected);
         }

         int position = mStableIds.getPosition(id);
         if (DEBUG) Log.d(TAG, "ITEM " + id + " CHANGED at pos: " + position);

         if (position >= 0) {
             mAdapter.notifyItemChanged(position, SelectionHelper.SELECTION_CHANGED_MARKER);
         } else {
             Log.w(TAG, "Item change notification received for unknown item: " + id);
         }
     }

     private void notifySelectionCleared(Selection selection) {
         for (String id: selection.mSelection) {
             notifyItemStateChanged(id, false);
         }
         for (String id: selection.mProvisionalSelection) {
             notifyItemStateChanged(id, false);
         }
     }

     /**
      * Notifies registered listeners when the selection has changed. This
      * notification should be sent only once a full series of changes
      * is complete, e.g. clearingSelection, or updating the single
      * selection from one item to another.
      */
     private void notifySelectionChanged() {
         int lastListenerIndex = mObservers.size() - 1;
         for (int i = lastListenerIndex; i >= 0; i--) {
             mObservers.get(i).onSelectionChanged();
         }
     }

     private void notifySelectionRestored() {
         int lastListenerIndex = mObservers.size() - 1;
         for (int i = lastListenerIndex; i >= 0; i--) {
             mObservers.get(i).onSelectionRestored();
         }
     }

     private void notifySelectionReset() {
         int lastListenerIndex = mObservers.size() - 1;
         for (int i = lastListenerIndex; i >= 0; i--) {
             mObservers.get(i).onSelectionReset();
         }
     }

     private void updateForRange(int begin, int end, boolean selected, @RangeType int type) {
         switch (type) {
             case RANGE_REGULAR:
                 updateForRegularRange(begin, end, selected);
                 break;
             case RANGE_PROVISIONAL:
                 updateForProvisionalRange(begin, end, selected);
                 break;
             default:
                 throw new IllegalArgumentException("Invalid range type: " + type);
         }
     }

     private void updateForRegularRange(int begin, int end, boolean selected) {
         checkArgument(end >= begin);

         for (int i = begin; i <= end; i++) {
             String id = mStableIds.getStableId(i);
             if (id == null) {
                 continue;
             }

             if (selected) {
                 select(id);
             } else {
                 deselect(id);
             }
         }
     }

     private void updateForProvisionalRange(int begin, int end, boolean selected) {
         checkArgument(end >= begin);

         for (int i = begin; i <= end; i++) {
             String id = mStableIds.getStableId(i);
             if (id == null) {
                 continue;
             }

             boolean changedState = false;
             if (selected) {
                 boolean canSelect = canSetState(id, true);
                 if (canSelect && !mSelection.mSelection.contains(id)) {
                     mSelection.mProvisionalSelection.add(id);
                     changedState = true;
                 }
             } else {
                 mSelection.mProvisionalSelection.remove(id);
                 changedState = true;
             }

             // Only notify item callbacks when something's state is actually changed in provisional
             // selection.
             if (changedState) {
                 notifyItemStateChanged(id, selected);
             }
         }

         notifySelectionChanged();
     }

     private final class AdapterObserver extends RecyclerView.AdapterDataObserver {
         @Override
         public void onChanged() {
             onDataSetChanged();
         }

         @Override
         public void onItemRangeChanged(
                 int startPosition, int itemCount, Object payload) {
             // No change in position. Ignore, since we assume
             // selection is a user driven activity. So changes
             // in properties of items shouldn't result in a
             // change of selection.
         }

         @Override
         public void onItemRangeInserted(int startPosition, int itemCount) {
             onDataSetItemRangeInserted(startPosition, itemCount);
         }

         @Override
         public void onItemRangeRemoved(int startPosition, int itemCount) {
             onDataSetItemRangeRemoved(startPosition, itemCount);
         }

         @Override
         public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
             throw new UnsupportedOperationException();
         }
     }

     private final class RangeCallbacks extends Range.Callbacks {
         @Override
         void updateForRange(int begin, int end, boolean selected, int type) {
             switch (type) {
                 case RANGE_REGULAR:
                     updateForRegularRange(begin, end, selected);
                     break;
                 case RANGE_PROVISIONAL:
                     updateForProvisionalRange(begin, end, selected);
                     break;
                 default:
                     throw new IllegalArgumentException(
                             "Invalid range type: " + type);
             }
         }
     }
 }
	/*
	* Copyright (C) 2015 The Android Open Source Project
	*
	* 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.
	*/

	package com.android.documentsui.selection;

	import static android.support.v4.util.Preconditions.checkArgument;
	import static android.support.v4.util.Preconditions.checkState;
	import static com.android.documentsui.selection.Shared.DEBUG;
	import static com.android.documentsui.selection.Shared.TAG;

	import android.support.annotation.IntDef;
	import android.support.v7.widget.RecyclerView;
	import android.support.v7.widget.RecyclerView.Adapter;
	import android.util.Log;

	import java.lang.annotation.Retention;
	import java.lang.annotation.RetentionPolicy;
	import java.util.ArrayList;
	import java.util.List;
	import java.util.Map;
	import java.util.Set;

	import javax.annotation.Nullable;

	/**
	* {@link SelectionHelper} providing support traditional multi-item selection on top
	* of {@link RecyclerView}.
	*
	* <p>The class supports running in a single-select mode, which can be enabled
	* by passing {@colde #MODE_SINGLE} to the constructor.
	*/
	public final class DefaultSelectionHelper extends SelectionHelper {

	public static final int MODE_MULTIPLE = 0;
	public static final int MODE_SINGLE = 1;

	@IntDef(flag = true, value = {
	MODE_MULTIPLE,
	MODE_SINGLE
	})
	@Retention(RetentionPolicy.SOURCE)
	public @interface SelectionMode {}

	private static final int RANGE_REGULAR = 0;

	/**
	* "Provisional" selection represents a overlay on the primary selection. A provisional
	* selection maybe be eventually added to the primary selection, or it may be abandoned.
	*
	* <p>E.g. BandController creates a provisional selection while a user is actively selecting
	* items with the band. Provisionally selected items are considered to be selected in
	* {@link Selection#contains(String)} and related methods. A provisional may be abandoned or
	* applied by selection components (like
	* {@link com.android.documentsui.selection.BandSelectionHelper}).
	*
	* <p>A provisional selection may intersect the primary selection, however clearing the
	* provisional selection will not affect the primary selection where the two may intersect.
	*/
	private static final int RANGE_PROVISIONAL = 1;
	@IntDef({
	RANGE_REGULAR,
	RANGE_PROVISIONAL
	})
	@Retention(RetentionPolicy.SOURCE)
	@interface RangeType {}

	private final Selection mSelection = new Selection();
	private final List<SelectionObserver> mObservers = new ArrayList<>(1);
	private final RecyclerView.Adapter<?> mAdapter;
	private final StableIdProvider mStableIds;
	private final SelectionPredicate mSelectionPredicate;
	private final RecyclerView.AdapterDataObserver mAdapterObserver;
	private final RangeCallbacks mRangeCallbacks;
	private final boolean mSingleSelect;

	private @Nullable Range mRange;

	/**
	* Creates a new instance.
	*
	* @param mode single or multiple selection mode. In single selection mode
	* users can only select a single item.
	* @param adapter {@link Adapter} for the RecyclerView this instance is coupled with.
	* @param stableIds client supplied class providing access to stable ids.
	* @param selectionPredicate A predicate allowing the client to disallow selection
	* of individual elements.
	*/
	public DefaultSelectionHelper(
	@SelectionMode int mode,
	RecyclerView.Adapter<?> adapter,
	StableIdProvider stableIds,
	SelectionPredicate selectionPredicate) {

	checkArgument(mode == MODE_SINGLE \|\| mode == MODE_MULTIPLE);
	checkArgument(adapter != null);
	checkArgument(stableIds != null);
	checkArgument(selectionPredicate != null);

	mAdapter = adapter;
	mStableIds = stableIds;
	mSelectionPredicate = selectionPredicate;
	mAdapterObserver = new AdapterObserver();
	mRangeCallbacks = new RangeCallbacks();

	mSingleSelect = mode == MODE_SINGLE;

	mAdapter.registerAdapterDataObserver(mAdapterObserver);
	}

	@Override
	public void addObserver(SelectionObserver callback) {
	checkArgument(callback != null);
	mObservers.add(callback);
	}

	@Override
	public boolean hasSelection() {
	return !mSelection.isEmpty();
	}

	@Override
	public Selection getSelection() {
	return mSelection;
	}

	@Override
	public void copySelection(Selection dest) {
	dest.copyFrom(mSelection);
	}

	@Override
	public boolean isSelected(String id) {
	return mSelection.contains(id);
	}

	@Override
	public void restoreSelection(Selection other) {
	setItemsSelectedQuietly(other.mSelection, true);
	// NOTE: We intentionally don't restore provisional selection. It's provisional.
	notifySelectionRestored();
	}

	@Override
	public boolean setItemsSelected(Iterable<String> ids, boolean selected) {
	boolean changed = setItemsSelectedQuietly(ids, selected);
	notifySelectionChanged();
	return changed;
	}

	private boolean setItemsSelectedQuietly(Iterable<String> ids, boolean selected) {
	boolean changed = false;
	for (String id: ids) {
	boolean itemChanged = selected
	? canSetState(id, true) && mSelection.add(id)
	: canSetState(id, false) && mSelection.remove(id);
	if (itemChanged) {
	notifyItemStateChanged(id, selected);
	}
	changed \|= itemChanged;
	}
	return changed;
	}

	@Override
	public void clearSelection() {
	if (!hasSelection()) {
	return;
	}

	Selection prev = clearSelectionQuietly();
	notifySelectionCleared(prev);
	notifySelectionChanged();
	}

	/**
	* Clears the selection, without notifying selection listeners.
	* Returns items in previous selection. Callers are responsible for notifying
	* listeners about changes.
	*/
	private Selection clearSelectionQuietly() {
	mRange = null;

	Selection prevSelection = new Selection();
	if (hasSelection()) {
	copySelection(prevSelection);
	mSelection.clear();
	}

	return prevSelection;
	}

	@Override
	public boolean select(String id) {
	checkArgument(id != null);

	if (!mSelection.contains(id)) {
	if (!canSetState(id, true)) {
	if (DEBUG) Log.d(TAG, "Select cancelled by selection predicate test.");
	return false;
	}

	// Enforce single selection policy.
	if (mSingleSelect && hasSelection()) {
	Selection prev = clearSelectionQuietly();
	notifySelectionCleared(prev);
	}

	mSelection.add(id);
	notifyItemStateChanged(id, true);
	notifySelectionChanged();

	return true;
	}

	return false;
	}

	@Override
	public boolean deselect(String id) {
	checkArgument(id != null);

	if (mSelection.contains(id)) {
	if (!canSetState(id, false)) {
	if (DEBUG) Log.d(TAG, "Deselect cancelled by selection predicate test.");
	return false;
	}
	mSelection.remove(id);
	notifyItemStateChanged(id, false);
	notifySelectionChanged();
	if (mSelection.isEmpty() && isRangeActive()) {
	// if there's nothing in the selection and there is an active ranger it results
	// in unexpected behavior when the user tries to start range selection: the item
	// which the ranger 'thinks' is the already selected anchor becomes unselectable
	endRange();
	}
	return true;
	}

	return false;
	}

	@Override
	public void startRange(int pos) {
	select(mStableIds.getStableId(pos));
	anchorRange(pos);
	}

	@Override
	public void extendRange(int pos) {
	extendRange(pos, RANGE_REGULAR);
	}

	@Override
	public void endRange() {
	mRange = null;
	// Clean up in case there was any leftover provisional selection
	clearProvisionalSelection();
	}

	@Override
	public void anchorRange(int position) {
	checkArgument(position != RecyclerView.NO_POSITION);

	// TODO: I'm not a fan of silently ignoring calls.
	// Determine if there are any cases where method can be called
	// w/o item already being selected. Else, tighten up the ship
	// and make this conditional guard into a proper precondition check.
	if (mSelection.contains(mStableIds.getStableId(position))) {
	mRange = new Range(mRangeCallbacks, position);
	}
	}

	@Override
	public void extendProvisionalRange(int pos) {
	extendRange(pos, RANGE_PROVISIONAL);
	}

	/**
	* Sets the end point for the current range selection, started by a call to
	* {@link #startRange(int)}. This function should only be called when a range selection
	* is active (see {@link #isRangeActive()}. Items in the range [anchor, end] will be
	* selected or in provisional select, depending on the type supplied. Note that if the type is
	* provisional selection, one should do {@link #mergeProvisionalSelection()} at some
	* point before calling on {@link #endRange()}.
	*
	* @param pos The new end position for the selection range.
	* @param type The type of selection the range should utilize.
	*/
	private void extendRange(int pos, @RangeType int type) {
	checkState(isRangeActive(), "Range start point not set.");

	mRange.extendSelection(pos, type);

	// We're being lazy here notifying even when something might not have changed.
	// To make this more correct, we'd need to update the Ranger class to return
	// information about what has changed.
	notifySelectionChanged();
	}

	@Override
	public void setProvisionalSelection(Set<String> newSelection) {
	Map<String, Boolean> delta = mSelection.setProvisionalSelection(newSelection);
	for (Map.Entry<String, Boolean> entry: delta.entrySet()) {
	notifyItemStateChanged(entry.getKey(), entry.getValue());
	}

	notifySelectionChanged();
	}

	@Override
	public void mergeProvisionalSelection() {
	mSelection.mergeProvisionalSelection();
	}

	@Override
	public void clearProvisionalSelection() {
	for (String id : mSelection.mProvisionalSelection) {
	notifyItemStateChanged(id, false);
	}
	mSelection.clearProvisionalSelection();
	}

	@Override
	public boolean isRangeActive() {
	return mRange != null;
	}

	private boolean canSetState(String id, boolean nextState) {
	return mSelectionPredicate.canSetStateForId(id, nextState);
	}

	private void onDataSetChanged() {
	// Update the selection to remove any disappeared IDs.
	mSelection.clearProvisionalSelection();
	mSelection.intersect(mStableIds.getStableIds());
	notifySelectionReset();

	for (String id : mSelection) {
	// If the underlying data set has changed, before restoring
	// selection we must re-verify that it can be selected.
	// Why? Because if the dataset has changed, then maybe the
	// selectability of an item has changed.
	if (!canSetState(id, true)) {
	deselect(id);
	} else {
	int lastListener = mObservers.size() - 1;
	for (int i = lastListener; i >= 0; i--) {
	mObservers.get(i).onItemStateChanged(id, true);
	}
	}
	}
	notifySelectionChanged();
	}

	private void onDataSetItemRangeInserted(int startPosition, int itemCount) {
	mSelection.clearProvisionalSelection();
	}

	private void onDataSetItemRangeRemoved(int startPosition, int itemCount) {
	checkArgument(startPosition >= 0);
	checkArgument(itemCount > 0);

	mSelection.clearProvisionalSelection();

	// Remove any disappeared IDs from the selection.
	//
	// Ideally there could be a cheaper approach, checking
	// each position individually, but since the source of
	// truth for stable ids (StableIdProvider) probably
	// it-self no-longer knows about the positions in question
	// we fall back to the sledge hammer approach.
	mSelection.intersect(mStableIds.getStableIds());
	}

	/**
	* Notifies registered listeners when the selection status of a single item
	* (identified by {@code position}) changes.
	*/
	private void notifyItemStateChanged(String id, boolean selected) {
	checkArgument(id != null);

	int lastListenerIndex = mObservers.size() - 1;
	for (int i = lastListenerIndex; i >= 0; i--) {
	mObservers.get(i).onItemStateChanged(id, selected);
	}

	int position = mStableIds.getPosition(id);
	if (DEBUG) Log.d(TAG, "ITEM " + id + " CHANGED at pos: " + position);

	if (position >= 0) {
	mAdapter.notifyItemChanged(position, SelectionHelper.SELECTION_CHANGED_MARKER);
	} else {
	Log.w(TAG, "Item change notification received for unknown item: " + id);
	}
	}

	private void notifySelectionCleared(Selection selection) {
	for (String id: selection.mSelection) {
	notifyItemStateChanged(id, false);
	}
	for (String id: selection.mProvisionalSelection) {
	notifyItemStateChanged(id, false);
	}
	}

	/**
	* Notifies registered listeners when the selection has changed. This
	* notification should be sent only once a full series of changes
	* is complete, e.g. clearingSelection, or updating the single
	* selection from one item to another.
	*/
	private void notifySelectionChanged() {
	int lastListenerIndex = mObservers.size() - 1;
	for (int i = lastListenerIndex; i >= 0; i--) {
	mObservers.get(i).onSelectionChanged();
	}
	}

	private void notifySelectionRestored() {
	int lastListenerIndex = mObservers.size() - 1;
	for (int i = lastListenerIndex; i >= 0; i--) {
	mObservers.get(i).onSelectionRestored();
	}
	}

	private void notifySelectionReset() {
	int lastListenerIndex = mObservers.size() - 1;
	for (int i = lastListenerIndex; i >= 0; i--) {
	mObservers.get(i).onSelectionReset();
	}
	}

	private void updateForRange(int begin, int end, boolean selected, @RangeType int type) {
	switch (type) {
	case RANGE_REGULAR:
	updateForRegularRange(begin, end, selected);
	break;
	case RANGE_PROVISIONAL:
	updateForProvisionalRange(begin, end, selected);
	break;
	default:
	throw new IllegalArgumentException("Invalid range type: " + type);
	}
	}

	private void updateForRegularRange(int begin, int end, boolean selected) {
	checkArgument(end >= begin);

	for (int i = begin; i <= end; i++) {
	String id = mStableIds.getStableId(i);
	if (id == null) {
	continue;
	}

	if (selected) {
	select(id);
	} else {
	deselect(id);
	}
	}
	}

	private void updateForProvisionalRange(int begin, int end, boolean selected) {
	checkArgument(end >= begin);

	for (int i = begin; i <= end; i++) {
	String id = mStableIds.getStableId(i);
	if (id == null) {
	continue;
	}

	boolean changedState = false;
	if (selected) {
	boolean canSelect = canSetState(id, true);
	if (canSelect && !mSelection.mSelection.contains(id)) {
	mSelection.mProvisionalSelection.add(id);
	changedState = true;
	}
	} else {
	mSelection.mProvisionalSelection.remove(id);
	changedState = true;
	}

	// Only notify item callbacks when something's state is actually changed in provisional
	// selection.
	if (changedState) {
	notifyItemStateChanged(id, selected);
	}
	}

	notifySelectionChanged();
	}

	private final class AdapterObserver extends RecyclerView.AdapterDataObserver {
	@Override
	public void onChanged() {
	onDataSetChanged();
	}

	@Override
	public void onItemRangeChanged(
	int startPosition, int itemCount, Object payload) {
	// No change in position. Ignore, since we assume
	// selection is a user driven activity. So changes
	// in properties of items shouldn't result in a
	// change of selection.
	}

	@Override
	public void onItemRangeInserted(int startPosition, int itemCount) {
	onDataSetItemRangeInserted(startPosition, itemCount);
	}

	@Override
	public void onItemRangeRemoved(int startPosition, int itemCount) {
	onDataSetItemRangeRemoved(startPosition, itemCount);
	}

	@Override
	public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
	throw new UnsupportedOperationException();
	}
	}

	private final class RangeCallbacks extends Range.Callbacks {
	@Override
	void updateForRange(int begin, int end, boolean selected, int type) {
	switch (type) {
	case RANGE_REGULAR:
	updateForRegularRange(begin, end, selected);
	break;
	case RANGE_PROVISIONAL:
	updateForProvisionalRange(begin, end, selected);
	break;
	default:
	throw new IllegalArgumentException(
	"Invalid range type: " + type);
	}
	}
	}
	}