anchor.diff:    Widget build(BuildContext context) {
       Widget cardCollection;
       if (_fixedSizeCards) {
  -      cardCollection = new ScrollableList (
  +      _invalidator = null;
  +      cardCollection = new ScrollableList(
           snapOffsetCallback: _snapToCenter ? _toSnapOffset : null,
  -        itemExtent: _cardModels[0].height,
  -        children: _cardModels.map((CardModel card) => _buildCard(context, card.value))
  +        itemExtent: kFixedCardHeight,
  +        children: _cardIndices.map/*<Widget>*/((int index) => _buildCard(context, index))
         );
       } else {
         cardCollection = new ScrollableMixedWidgetList(
  
positive.code:   }
  
    double _fixedSizeToSnapOffset(double scrollOffset) {
      double cardHeight = _cardModels[0].height;
      int cardIndex = (scrollOffset.clamp(0.0, cardHeight * (_cardModels.length - 1)) / cardHeight).floor();
      return cardIndex * cardHeight + cardHeight * 0.5;
    }
  
    double _toSnapOffset(double scrollOffset, Size containerSize) {
  
negative.code:   static const String _sunshineURL = "http://www.walltor.com/images/wallpaper/good-morning-sunshine-58540.jpg";
  
    static const double kCardMargins = 8.0;
    static const double kFixedCardHeight = 100.0;
  
    final TextStyle backgroundTextStyle =
      Typography.white.title.copyWith(textAlign: TextAlign.center);
  