content: /*
   * Copyright (C) 2013 The Android Open Source Project
   * Copyright 2013 Niek Haarman
   *
   * 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.nhaarman.listviewanimations.widget;
  
  import android.content.Context;
  import android.graphics.Bitmap;
  import android.graphics.Canvas;
  import android.graphics.Rect;
  import android.graphics.drawable.BitmapDrawable;
  import android.graphics.drawable.Drawable;
  import android.util.AttributeSet;
  import android.util.DisplayMetrics;
  import android.view.MotionEvent;
  import android.view.View;
  import android.view.ViewConfiguration;
  import android.view.ViewGroup;
  import android.view.ViewTreeObserver;
  import android.widget.AbsListView;
  import android.widget.AdapterView;
  import android.widget.BaseAdapter;
  import android.widget.HeaderViewListAdapter;
  import android.widget.ListAdapter;
  import android.widget.ListView;
  
  import com.nhaarman.listviewanimations.itemmanipulation.swipedismiss.SwipeOnTouchListener;
  import com.nineoldandroids.animation.Animator;
  import com.nineoldandroids.animation.AnimatorListenerAdapter;
  import com.nineoldandroids.animation.ObjectAnimator;
  import com.nineoldandroids.animation.TypeEvaluator;
  import com.nineoldandroids.animation.ValueAnimator;
  import com.nineoldandroids.view.ViewHelper;
  
  /**
   * The DynamicListView is an extension of {@link ListView} that supports cell dragging
   * and swapping.
   * </p>
   * Make sure your adapter has stable ids, and override {@link ListAdapter#hasStableIds()} to return true.</br>
   * </p>
   * This layout is in charge of positioning the hover cell in the correct location
   * on the screen in response to user touch events. It uses the position of the
   * hover cell to determine when two cells should be swapped. If two cells should
   * be swapped, all the corresponding data set and layout changes are handled here.
   * </p>
   * If no cell is selected, all the touch events are passed down to the ListView
   * and behave normally. If one of the items in the ListView experiences a
   * long press event, the contents of its current visible state are captured as
   * a bitmap and its visibility is set to INVISIBLE. A hover cell is then created and
   * added to this layout as an overlaying BitmapDrawable above the ListView. Once the
   * hover cell is translated some distance to signify an item swap, a data set change
   * accompanied by animation takes place. When the user releases the hover cell,
   * it animates into its corresponding position in the ListView.
   * </p>
   * When the hover cell is either above or below the bounds of the ListView, this
   * ListView also scrolls on its own so as to reveal additional content.
   * </p>
   * See http://youtu.be/_BZIvjMgH-Q
   */
  public class DynamicListView extends ListView {
  
      private int mOriginalTranscriptMode;
  
      public interface OnHoverCellListener {
          public Drawable onHoverCellCreated(Drawable hoverCellDrawable);
      }
  
      /**
       * Implement this interface to be notified of ordering changes. Call {@link #setOnItemMovedListener(com.nhaarman.listviewanimations.widget.DynamicListView.OnItemMovedListener)}.
       */
      public interface OnItemMovedListener {
          /**
           * Called after an item is dropped and moved.
           *
           * @param newPosition the new position of the item.
           */
          public void onItemMoved(int newPosition);
      }
  
      private final int SMOOTH_SCROLL_AMOUNT_AT_EDGE = 15;
      private final int MOVE_DURATION = 150;
  
      private int mLastEventY = -1, mLastEventX = -1;
  
      private int mDownY = -1;
      private int mDownX = -1;
  
      private int mTotalOffset = 0;
  
      private boolean mCellIsMobile = false;
      private boolean mIsMobileScrolling = false;
      private int mSmoothScrollAmountAtEdge = 0;
  
      private final int INVALID_ID = -1;
      private long mAboveItemId = INVALID_ID;
      private long mMobileItemId = INVALID_ID;
      private long mBelowItemId = INVALID_ID;
  
      private Drawable mHoverCell;
      private Rect mHoverCellCurrentBounds;
      private Rect mHoverCellOriginalBounds;
  
      private final int INVALID_POINTER_ID = -1;
      private int mActivePointerId = INVALID_POINTER_ID;
  
      private boolean mIsWaitingForScrollFinish = false;
      private int mScrollState = OnScrollListener.SCROLL_STATE_IDLE;
  
      private OnTouchListener mOnTouchListener;
      private boolean mIsParentHorizontalScrollContainer;
      private int mResIdOfDynamicTouchChild;
      private boolean mDynamicTouchChildTouched;
      private int mSlop;
  
      private boolean mSkipCallingOnTouchListener;
  
      private OnHoverCellListener mOnHoverCellListener;
  
      private OnItemMovedListener mOnItemMovedListener;
      private int mLastMovedToIndex;
  
      public DynamicListView(Context context) {
          super(context);
          init(context);
      }
  
      public DynamicListView(Context context, AttributeSet attrs, int defStyle) {
          super(context, attrs, defStyle);
          init(context);
      }
  
      public DynamicListView(Context context, AttributeSet attrs) {
          super(context, attrs);
          init(context);
      }
  
      public void init(Context context) {
          setOnItemLongClickListener(mOnItemLongClickListener);
          setOnScrollListener(mScrollListener);
          DisplayMetrics metrics = context.getResources().getDisplayMetrics();
          mSmoothScrollAmountAtEdge = (int) (SMOOTH_SCROLL_AMOUNT_AT_EDGE / metrics.density);
          ViewConfiguration vc = ViewConfiguration.get(getContext());
          mSlop = vc.getScaledTouchSlop();
      }
  
      public void setAdapter(BaseAdapter adapter) {
          super.setAdapter(adapter);
      }
  
      @Override
      @Deprecated
      /**
       * @deprecated use #setAdapter(BaseAdapter) instead.
       */
      public void setAdapter(ListAdapter adapter) {
          if (!(adapter instanceof BaseAdapter)) {
              throw new IllegalArgumentException("DynamicListView needs a BaseAdapter!");
          }
          super.setAdapter(adapter);
      }
  
      /**
       * Listens for long clicks on any items in the listview. When a cell has
       * been selected, the hover cell is created and set up.
       */
      private OnItemLongClickListener mOnItemLongClickListener = new OnItemLongClickListener() {
          public boolean onItemLongClick(AdapterView<?> arg0, View arg1, int pos, long id) {
              if (mResIdOfDynamicTouchChild == 0) {
                  mDynamicTouchChildTouched = true;
                  makeCellMobile();
                  return true;
              }
              return false;
          }
      };
  
      private void makeCellMobile() {
          int position = pointToPosition(mDownX, mDownY);
          int itemNum = position - getFirstVisiblePosition();
          View selectedView = getChildAt(itemNum);
          if (selectedView == null || position < getHeaderViewsCount() || position >= getAdapter().getCount() - getHeaderViewsCount()) {
              return;
          }
  
          mOriginalTranscriptMode = getTranscriptMode();
          setTranscriptMode(TRANSCRIPT_MODE_NORMAL);
  
  
          mTotalOffset = 0;
  
          mMobileItemId = getAdapter().getItemId(position);
          mHoverCell = getAndAddHoverView(selectedView);
          if (mOnHoverCellListener != null) {
              mHoverCell = mOnHoverCellListener.onHoverCellCreated(mHoverCell);
          }
          selectedView.setVisibility(INVISIBLE);
  
          mCellIsMobile = true;
          getParent().requestDisallowInterceptTouchEvent(true);
  
          updateNeighborViewsForId(mMobileItemId);
      }
  
      /**
       * Creates the hover cell with the appropriate bitmap and of appropriate
       * size. The hover cell's BitmapDrawable is drawn on top of the bitmap every
       * single time an invalidate call is made.
       */
      private BitmapDrawable getAndAddHoverView(View v) {
          int w = v.getWidth();
          int h = v.getHeight();
          int top = v.getTop();
          int left = v.getLeft();
  
          Bitmap b = getBitmapFromView(v);
  
          BitmapDrawable drawable = new BitmapDrawable(getResources(), b);
  
          mHoverCellOriginalBounds = new Rect(left, top, left + w, top + h);
          mHoverCellCurrentBounds = new Rect(mHoverCellOriginalBounds);
  
          drawable.setBounds(mHoverCellCurrentBounds);
  
          return drawable;
      }
  
      /**
       * Returns a bitmap showing a screenshot of the view passed in.
       */
      private Bitmap getBitmapFromView(View v) {
          Bitmap bitmap = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.ARGB_8888);
          Canvas canvas = new Canvas(bitmap);
          v.draw(canvas);
          return bitmap;
      }
  
      /**
       * Stores a reference to the views above and below the item currently
       * corresponding to the hover cell. It is important to note that if this
       * item is either at the top or bottom of the list, mAboveItemId or mBelowItemId
       * may be invalid.
       */
      private void updateNeighborViewsForId(long itemId) {
          int position = getPositionForId(itemId);
          ListAdapter adapter = getAdapter();
          if (!adapter.hasStableIds()) {
              throw new IllegalStateException("Adapter doesn't have stable ids! Make sure your adapter has stable ids, and override hasStableIds() to return true.");
          }
  
          mAboveItemId = position - 1 >= 0 ? adapter.getItemId(position - 1) : INVALID_ROW_ID;
          mBelowItemId = position + 1 < adapter.getCount() ? adapter.getItemId(position + 1) : INVALID_ROW_ID;
      }
  
      /**
       * Retrieves the view in the list corresponding to itemId
       */
      private View getViewForId(long itemId) {
          int firstVisiblePosition = getFirstVisiblePosition();
          ListAdapter adapter = getAdapter();
          if (!adapter.hasStableIds()) {
              throw new IllegalStateException("Adapter doesn't have stable ids! Make sure your adapter has stable ids, and override hasStableIds() to return true.");
          }
  
          for (int i = 0; i < getChildCount(); i++) {
              View v = getChildAt(i);
              int position = firstVisiblePosition + i;
              long id = adapter.getItemId(position);
              if (id == itemId) {
                  return v;
              }
          }
          return null;
      }
  
      /**
       * Retrieves the position in the list corresponding to itemId
       */
      private int getPositionForId(long itemId) {
          View v = getViewForId(itemId);
          if (v == null) {
              return -1;
          } else {
              return getPositionForView(v);
          }
      }
  
      /**
       * dispatchDraw gets invoked when all the child views are about to be drawn.
       * By overriding this method, the hover cell (BitmapDrawable) can be drawn
       * over the listview's items whenever the listview is redrawn.
       */
      @Override
      protected void dispatchDraw(Canvas canvas) {
          super.dispatchDraw(canvas);
          if (mHoverCell != null) {
              mHoverCell.draw(canvas);
          }
      }
  
      @Override
      public void setOnTouchListener(OnTouchListener l) {
          mOnTouchListener = l;
      }
  
      public void setOnHoverCellListener(OnHoverCellListener onHoverCellListener) {
          mOnHoverCellListener = onHoverCellListener;
      }
  
      private Rect getChildViewRect(View parentView, View childView) {
          final Rect childRect = new Rect(childView.getLeft(), childView.getTop(), childView.getRight(), childView.getBottom());
          if (parentView == childView) {
              return childRect;
          }
  
          ViewGroup parent;
          while ((parent = (ViewGroup) childView.getParent()) != parentView) {
              childRect.offset(parent.getLeft(), parent.getTop());
              childView = parent;
          }
  
          return childRect;
      }
  
      @Override
      public boolean onTouchEvent(MotionEvent event) {
          if (mSkipCallingOnTouchListener) {
              return super.onTouchEvent(event);
          }
  
          if (mOnTouchListener instanceof SwipeOnTouchListener) {
              if (((SwipeOnTouchListener) mOnTouchListener).isSwiping()) {
                  mSkipCallingOnTouchListener = true;
                  boolean retVal = mOnTouchListener.onTouch(this, event);
                  mSkipCallingOnTouchListener = false;
                  return retVal || super.onTouchEvent(event);
              }
          }
  
          switch (event.getAction() & MotionEvent.ACTION_MASK) {
              case MotionEvent.ACTION_DOWN:
                  mDownX = (int) event.getX();
                  mDownY = (int) event.getY();
                  mActivePointerId = event.getPointerId(0);
  
                  mDynamicTouchChildTouched = false;
                  if (mResIdOfDynamicTouchChild != 0) {
                      mIsParentHorizontalScrollContainer = false;
  
                      int position = pointToPosition(mDownX, mDownY);
                      int childNum = (position != INVALID_POSITION) ? position - getFirstVisiblePosition() : -1;
                      View itemView = (childNum >= 0) ? getChildAt(childNum) : null;
                      View childView = (itemView != null) ? itemView.findViewById(mResIdOfDynamicTouchChild) : null;
                      if (childView != null) {
                          final Rect childRect = getChildViewRect(this, childView);
                          if (childRect.contains(mDownX, mDownY)) {
                              mDynamicTouchChildTouched = true;
                              getParent().requestDisallowInterceptTouchEvent(true);
                          }
                      }
                  }
  
                  if (mIsParentHorizontalScrollContainer) {
                      // Do it now and don't wait until the user moves more than the
                      // slop factor.
                      getParent().requestDisallowInterceptTouchEvent(true);
                  }
                  break;
              case MotionEvent.ACTION_MOVE:
                  if (mActivePointerId == INVALID_POINTER_ID) {
                      break;
                  }
  
                  int pointerIndex = event.findPointerIndex(mActivePointerId);
  
                  mLastEventY = (int) event.getY(pointerIndex);
                  mLastEventX = (int) event.getX(pointerIndex);
                  int deltaY = mLastEventY - mDownY;
                  int deltaX = mLastEventX - mDownX;
  
                  if (!mCellIsMobile && mDynamicTouchChildTouched) {
                      if (Math.abs(deltaY) > mSlop && Math.abs(deltaY) > Math.abs(deltaX)) {
                          makeCellMobile();
  
                          // Cancel ListView's touch (un-highlighting the item)
                          MotionEvent cancelEvent = MotionEvent.obtain(event);
                          cancelEvent.setAction(MotionEvent.ACTION_CANCEL | (event.getActionIndex() << MotionEvent.ACTION_POINTER_INDEX_SHIFT));
                          super.onTouchEvent(cancelEvent);
                          cancelEvent.recycle();
                      }
                  }
  
                  if (mCellIsMobile) {
                      mHoverCellCurrentBounds.offsetTo(mHoverCellOriginalBounds.left, mHoverCellOriginalBounds.top + deltaY + mTotalOffset);
                      mHoverCell.setBounds(mHoverCellCurrentBounds);
                      invalidate();
  
                      handleCellSwitch();
  
                      mIsMobileScrolling = false;
                      handleMobileCellScroll();
                  }
                  break;
              case MotionEvent.ACTION_UP:
                  mDynamicTouchChildTouched = false;
                  touchEventsEnded();
                  break;
              case MotionEvent.ACTION_CANCEL:
                  mDynamicTouchChildTouched = false;
                  touchEventsCancelled();
                  break;
              case MotionEvent.ACTION_POINTER_UP:
              /*
               * If a multitouch event took place and the original touch dictating
  			 * the movement of the hover cell has ended, then the dragging event
  			 * ends and the hover cell is animated to its corresponding position
  			 * in the listview.
  			 */
                  pointerIndex = (event.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
                  final int pointerId = event.getPointerId(pointerIndex);
                  if (pointerId == mActivePointerId) {
                      mDynamicTouchChildTouched = false;
                      touchEventsEnded();
                  }
                  break;
              default:
                  break;
          }
  
          if (mCellIsMobile) {
              return false;
          } else if (mOnTouchListener != null) {
              mSkipCallingOnTouchListener = true;
              boolean retVal = mOnTouchListener.onTouch(this, event);
              mSkipCallingOnTouchListener = false;
              if (retVal) {
                  return true;
              }
          }
          return super.onTouchEvent(event);
      }
  
      /**
       * This method determines whether the hover cell has been shifted far enough
       * to invoke a cell swap. If so, then the respective cell swap candidate is
       * determined and the data set is changed. Upon posting a notification of the
       * data set change, a layout is invoked to place the cells in the right place.
       * Using a ViewTreeObserver and a corresponding OnPreDrawListener, we can
       * offset the cell being swapped to where it previously was and then animate it to
       * its new position.
       */
      private void handleCellSwitch() {
          final int deltaY = mLastEventY - mDownY;
          int deltaYTotal = mHoverCellOriginalBounds.top + mTotalOffset + deltaY;
  
          View belowView = getViewForId(mBelowItemId);
          View mobileView = getViewForId(mMobileItemId);
          View aboveView = getViewForId(mAboveItemId);
  
          boolean isBelow = (belowView != null) && (deltaYTotal > belowView.getTop());
          boolean isAbove = (aboveView != null) && (deltaYTotal < aboveView.getTop());
  
          if (isBelow || isAbove) {
  
              final long switchItemId = isBelow ? mBelowItemId : mAboveItemId;
              View switchView = isBelow ? belowView : aboveView;
              final int originalItem = getPositionForView(mobileView);
  
              if (switchView == null) {
                  updateNeighborViewsForId(mMobileItemId);
                  return;
              }
  
              if (getPositionForView(switchView) < getHeaderViewsCount()) {
                  return;
              }
              swapElements(originalItem, getPositionForView(switchView));
  
              BaseAdapter adapter;
              if (getAdapter() instanceof HeaderViewListAdapter) {
                  adapter = (BaseAdapter) ((HeaderViewListAdapter) getAdapter()).getWrappedAdapter();
              } else {
                  adapter = (BaseAdapter) getAdapter();
              }
              adapter.notifyDataSetChanged();
  
              mDownY = mLastEventY;
              mDownX = mLastEventX;
  
              final int switchViewStartTop = switchView.getTop();
  
              mobileView.setVisibility(View.VISIBLE);
              switchView.setVisibility(View.INVISIBLE);
  
              updateNeighborViewsForId(mMobileItemId);
  
              final ViewTreeObserver observer = getViewTreeObserver();
              observer.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
                  public boolean onPreDraw() {
                      observer.removeOnPreDrawListener(this);
  
                      View switchView = getViewForId(switchItemId);
  
                      mTotalOffset += deltaY;
  
                      int switchViewNewTop = switchView.getTop();
                      int delta = switchViewStartTop - switchViewNewTop;
  
                      ViewHelper.setTranslationY(switchView, delta);
  
                      ObjectAnimator animator = ObjectAnimator.ofFloat(switchView, "translationY", 0);
                      animator.setDuration(MOVE_DURATION);
                      animator.start();
  
                      return true;
                  }
              });
          }
      }
  
      private void swapElements(int indexOne, int indexTwo) {
          mLastMovedToIndex = indexTwo;
          ListAdapter adapter = getAdapter();
  
          if (adapter instanceof HeaderViewListAdapter) {
              adapter = ((HeaderViewListAdapter) adapter).getWrappedAdapter();
          }
  
          if (adapter instanceof Swappable) {
              ((Swappable) adapter).swapItems(indexOne - getHeaderViewsCount(), indexTwo - getHeaderViewsCount());
          }
      }
  
      /**
       * Resets all the appropriate fields to a default state while also animating
       * the hover cell back to its correct location.
       */
      private void touchEventsEnded() {
          final View mobileView = getViewForId(mMobileItemId);
          if (mCellIsMobile || mIsWaitingForScrollFinish) {
              mCellIsMobile = false;
              mIsWaitingForScrollFinish = false;
              mIsMobileScrolling = false;
              mActivePointerId = INVALID_POINTER_ID;
  
              /* Restore the transcript mode */
              setTranscriptMode(mOriginalTranscriptMode);
  
              // If the autoscroller has not completed scrolling, we need to wait
              // for it to
              // finish in order to determine the final location of where the
              // hover cell
              // should be animated to.
              if (mScrollState != OnScrollListener.SCROLL_STATE_IDLE) {
                  mIsWaitingForScrollFinish = true;
                  return;
              }
  
              mHoverCellCurrentBounds.offsetTo(mHoverCellOriginalBounds.left, mobileView.getTop());
  
              ObjectAnimator hoverViewAnimator = ObjectAnimator.ofObject(mHoverCell, "bounds", sBoundEvaluator, mHoverCellCurrentBounds);
              hoverViewAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                  @Override
                  public void onAnimationUpdate(ValueAnimator valueAnimator) {
                      invalidate();
                  }
              });
              hoverViewAnimator.addListener(new AnimatorListenerAdapter() {
                  @Override
                  public void onAnimationStart(Animator animation) {
                      setEnabled(false);
                  }
  
                  @Override
                  public void onAnimationEnd(Animator animation) {
                      mAboveItemId = INVALID_ID;
                      mMobileItemId = INVALID_ID;
                      mBelowItemId = INVALID_ID;
                      mobileView.setVisibility(VISIBLE);
                      mHoverCell = null;
                      setEnabled(true);
                      invalidate();
                      if (mOnItemMovedListener != null) {
                          mOnItemMovedListener.onItemMoved(mLastMovedToIndex - getHeaderViewsCount());
                      }
                  }
              });
              hoverViewAnimator.start();
          } else {
              touchEventsCancelled();
          }
      }
  
      /**
       * Resets all the appropriate fields to a default state.
       */
      private void touchEventsCancelled() {
          View mobileView = getViewForId(mMobileItemId);
          if (mCellIsMobile) {
              mAboveItemId = INVALID_ID;
              mMobileItemId = INVALID_ID;
              mBelowItemId = INVALID_ID;
              mobileView.setVisibility(VISIBLE);
              mHoverCell = null;
              invalidate();
          }
          mCellIsMobile = false;
          mIsMobileScrolling = false;
          mActivePointerId = INVALID_POINTER_ID;
      }
  
      /**
       * This TypeEvaluator is used to animate the BitmapDrawable back to its
       * final location when the user lifts his finger by modifying the
       * BitmapDrawable's bounds.
       */
      private final static TypeEvaluator<Rect> sBoundEvaluator = new TypeEvaluator<Rect>() {
          public Rect evaluate(float fraction, Rect startValue, Rect endValue) {
              return new Rect(interpolate(startValue.left, endValue.left, fraction), interpolate(startValue.top, endValue.top, fraction), interpolate(startValue.right, endValue.right, fraction),
                      interpolate(startValue.bottom, endValue.bottom, fraction));
          }
  
          public int interpolate(int start, int end, float fraction) {
              return (int) (start + fraction * (end - start));
          }
      };
  
      /**
       * Determines whether this listview is in a scrolling state invoked
       * by the fact that the hover cell is out of the bounds of the listview;
       */
      private void handleMobileCellScroll() {
          mIsMobileScrolling = handleMobileCellScroll(mHoverCellCurrentBounds);
      }
  
      /**
       * This method is in charge of determining if the hover cell is above
       * or below the bounds of the listview. If so, the listview does an appropriate
       * upward or downward smooth scroll so as to reveal new items.
       */
      private boolean handleMobileCellScroll(Rect r) {
          int offset = computeVerticalScrollOffset();
          int height = getHeight();
          int extent = computeVerticalScrollExtent();
          int range = computeVerticalScrollRange();
          int hoverViewTop = r.top;
          int hoverHeight = r.height();
  
          if (hoverViewTop <= 0 && offset > 0) {
              smoothScrollBy(-mSmoothScrollAmountAtEdge, 0);
              return true;
          }
  
          if (hoverViewTop + hoverHeight >= height && (offset + extent) < range) {
              smoothScrollBy(mSmoothScrollAmountAtEdge, 0);
              return true;
          }
  
          return false;
      }
  
      public void setIsParentHorizontalScrollContainer(boolean isParentHorizontalScrollContainer) {
          mIsParentHorizontalScrollContainer = (mResIdOfDynamicTouchChild == 0) && isParentHorizontalScrollContainer;
      }
  
      public boolean isParentHorizontalScrollContainer() {
          return mIsParentHorizontalScrollContainer;
      }
  
      public void setDynamicTouchChild(int childResId) {
          mResIdOfDynamicTouchChild = childResId;
          if (childResId != 0) {
              setIsParentHorizontalScrollContainer(false);
          }
      }
  
      /**
       * This scroll listener is added to the listview in order to handle cell swapping
       * when the cell is either at the top or bottom edge of the listview. If the hover
       * cell is at either edge of the listview, the listview will begin scrolling. As
       * scrolling takes place, the listview continuously checks if new cells became visible
       * and determines whether they are potential candidates for a cell swap.
       */
      private OnScrollListener mScrollListener = new OnScrollListener() {
  
          private int mPreviousFirstVisibleItem = -1;
          private int mPreviousVisibleItemCount = -1;
          private int mCurrentFirstVisibleItem;
          private int mCurrentVisibleItemCount;
          private int mCurrentScrollState;
  
          public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
              mCurrentFirstVisibleItem = firstVisibleItem;
              mCurrentVisibleItemCount = visibleItemCount;
  
              mPreviousFirstVisibleItem = (mPreviousFirstVisibleItem == -1) ? mCurrentFirstVisibleItem : mPreviousFirstVisibleItem;
              mPreviousVisibleItemCount = (mPreviousVisibleItemCount == -1) ? mCurrentVisibleItemCount : mPreviousVisibleItemCount;
  
              checkAndHandleFirstVisibleCellChange();
              checkAndHandleLastVisibleCellChange();
  
              mPreviousFirstVisibleItem = mCurrentFirstVisibleItem;
              mPreviousVisibleItemCount = mCurrentVisibleItemCount;
          }
  
          @Override
          public void onScrollStateChanged(AbsListView view, int scrollState) {
              mCurrentScrollState = scrollState;
              mScrollState = scrollState;
              isScrollCompleted();
          }
  
          /**
           * This method is in charge of invoking 1 of 2 actions. Firstly, if the listview
           * is in a state of scrolling invoked by the hover cell being outside the bounds
           * of the listview, then this scrolling event is continued. Secondly, if the hover
           * cell has already been released, this invokes the animation for the hover cell
           * to return to its correct position after the listview has entered an idle scroll
           * state.
           */
          private void isScrollCompleted() {
              if (mCurrentVisibleItemCount > 0 && mCurrentScrollState == SCROLL_STATE_IDLE) {
                  if (mCellIsMobile && mIsMobileScrolling) {
                      handleMobileCellScroll();
                  } else if (mIsWaitingForScrollFinish) {
                      touchEventsEnded();
                  }
              }
          }
  
          /**
           * Determines if the listview scrolled up enough to reveal a new cell at the
           * top of the list. If so, then the appropriate parameters are updated.
           */
          public void checkAndHandleFirstVisibleCellChange() {
              if (mCurrentFirstVisibleItem != mPreviousFirstVisibleItem) {
                  if (mCellIsMobile && mMobileItemId != INVALID_ID) {
                      updateNeighborViewsForId(mMobileItemId);
                      handleCellSwitch();
                  }
              }
          }
  
          /**
           * Determines if the listview scrolled down enough to reveal a new cell at the
           * bottom of the list. If so, then the appropriate parameters are updated.
           */
          public void checkAndHandleLastVisibleCellChange() {
              int currentLastVisibleItem = mCurrentFirstVisibleItem + mCurrentVisibleItemCount;
              int previousLastVisibleItem = mPreviousFirstVisibleItem + mPreviousVisibleItemCount;
              if (currentLastVisibleItem != previousLastVisibleItem) {
                  if (mCellIsMobile && mMobileItemId != INVALID_ID) {
                      updateNeighborViewsForId(mMobileItemId);
                      handleCellSwitch();
                  }
              }
          }
      };
  
      /**
       * Set the {@link com.nhaarman.listviewanimations.widget.DynamicListView.OnItemMovedListener} to be notified when an item is dropped.
       */
      public void setOnItemMovedListener(OnItemMovedListener onItemMovedListener) {
          this.mOnItemMovedListener = onItemMovedListener;
      }
  
      /**
       * Interface, usually implemented by a {@link com.nhaarman.listviewanimations.BaseAdapterDecorator},
       * that indicates that it can swap the visual position of two list items.
       *
       * @author Anton Spaans on 9/11/13.
       */
      public interface Swappable {
  
          /**
           * Swaps the item on the first adapter position with the item on the second adapter position.
           * Be sure to call {@link android.widget.BaseAdapter#notifyDataSetChanged()} if appropriate when implementing this method.
           *
           * @param positionOne First adapter position.
           * @param positionTwo Second adapter position.
           */
          public void swapItems(int positionOne, int positionTwo);
      }
  }