phase3: shop.dart NotificationListener return bool

lib/widgets/general/carousel.dart

@@ -44,7 +44,7 @@ class CarouselState extends State<Carousel> {
             duration: widget.animationDuration, curve: Curves.linear);
         if (!reverse) {
           _currentPage += 1;
-          if (_currentPage == widget.pages.length) {
+          if (_currentPage == widget.pages!.length) {
             _currentPage -= 1;
             reverse = true;
           }
@@ -77,7 +77,7 @@ class CarouselState extends State<Carousel> {
           color: Style.backgroundColor,
           child: new PageView(
             controller: _pageController,
-            children: widget.pages,
+            children: widget.pages!,
             onPageChanged: (index) {
               _currentPage = index;
               _indicatorStateKey.currentState!.changeIndex(index);
@@ -91,7 +91,7 @@ class CarouselState extends State<Carousel> {
           child: new Align(
             child: new Indicator(
               key: _indicatorStateKey,
-              count: widget.pages.length,
+              count: widget.pages!.length,
             ),
             alignment: Alignment.center,
           ),
@@ -124,7 +124,7 @@ class IndicatorState extends State<Indicator> {
   @override
   Widget build(BuildContext context) {
     var indicators = <Widget>[];
-    for (var i = 0; i < widget.count; ++i) {
+    for (var i = 0; i < widget.count!; ++i) {
       indicators.add(new Container(
         width: 5.0,
         height: 5.0,
@@ -135,7 +135,7 @@ class IndicatorState extends State<Indicator> {
       ));
     }
     return new SizedBox(
-      width: widget.count * 15.0,
+      width: widget.count! * 15.0,
       height: 30.0,
       child: new Row(
         children: indicators,

lib/widgets/mobile/shop.dart

@@ -1324,13 +1324,13 @@ class ShopState extends State<Shop>
         onNotification: (ScrollUpdateNotification notification) {
           if (!displayProductByCategoryClick) {
             if (_categoryIndexChange) {
-              return;
+              return false;
             }
             int index = _getCategoryIndexByRightScrollHeight(
                 notification.metrics.pixels);
             _setCategoryByProductScrolledIndex(index);
           }
-          return;
+          return false;
         },
         child: new ListView.builder(
             physics: ClampingScrollPhysics(),