bug fixes and add new samples

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/material/cards_demo.cs

 {
     public static class CardsDemoUtils
     {
-        public static readonly string _kGalleryAssetsPackage = "flutter_gallery_assets";
+        public static readonly string _kGalleryAssetsPackage = "StreamingAssets/gallery/";
     }
 
     internal enum CardDemoType
             D.assert(description != null);
             D.assert(city != null);
             D.assert(location != null);
+
+            this.assetName = assetName;
+            this.assetPackage = assetPackage;
+            this.title = title;
+            this.description = description;
+            this.city = city;
+            this.location = location;
+            this.type = type;
         }
 
         public readonly string assetName;

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/material/chip_demo.cs

 
         public static readonly Dictionary<string, string> _avatars = new Dictionary<string, string>()
         {
-            {"hammer", "people/square/ali.png"},
-            {"chisel", "people/square/sandra.png"},
-            {"fryer", "people/square/trevor.png"},
-            {"fabricator", "people/square/stella.png"},
-            {"customer", "people/square/peter.png"},
+            {"hammer", "StreamingAssets/gallery/people/square/ali.png"},
+            {"chisel", "StreamingAssets/gallery/people/square/sandra.png"},
+            {"fryer", "StreamingAssets/gallery/people/square/trevor.png"},
+            {"fabricator", "StreamingAssets/gallery/people/square/stella.png"},
+            {"customer", "StreamingAssets/gallery/people/square/peter.png"},
         };
 
         public static readonly Dictionary<string, HashSet<string>> _toolActions =

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/material/data_table_demo.cs

             );
         }
 
-        private new int rowCount => this._desserts.Count;
+        public override int rowCount => this._desserts.Count;
-        private new bool isRowCountApproximate => false;
+        public override bool isRowCountApproximate => false;
-        private new int selectedRowCount => this._selectedCount;
+        public override int selectedRowCount => this._selectedCount;
 
         public void _selectAll(bool isChecked)
         {

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/gallery/demos.cs

                     category: GalleryDemoCategory._kMaterialComponents,
                     routeName: ButtonsDemo.routeName,
                     buildRoute: (BuildContext context) => new ButtonsDemo()
-                )
+                ),
+                new GalleryDemo(
+                    title: "Cards",
+                    subtitle: "Baseline cards with rounded corners",
+                    icon: GalleryIcons.cards,
+                    category: GalleryDemoCategory._kMaterialComponents,
+                    routeName: CardsDemo.routeName,
+                    documentationUrl: "https://docs.flutter.io/flutter/material/Card-class.html",
+                    buildRoute: (BuildContext context) => new CardsDemo()
+                ),
+                new GalleryDemo(
+                    title: "Chips",
+                    subtitle: "Labeled with delete buttons and avatars",
+                    icon: GalleryIcons.chips,
+                    category: GalleryDemoCategory._kMaterialComponents,
+                    routeName: ChipDemo.routeName,
+                    documentationUrl: "https://docs.flutter.io/flutter/material/Chip-class.html",
+                    buildRoute: (BuildContext context) => new ChipDemo()
+                ),
+                new GalleryDemo(
+                    title: "Data tables",
+                    subtitle: "Rows and columns",
+                    icon: GalleryIcons.data_table,
+                    category: GalleryDemoCategory._kMaterialComponents,
+                    routeName: DataTableDemo.routeName,
+                    documentationUrl: "https://docs.flutter.io/flutter/material/PaginatedDataTable-class.html",
+                    buildRoute: (BuildContext context) => new DataTableDemo()
+                ),
             };
 
             return galleryDemos;

com.unity.uiwidgets/Runtime/material/data_table.cs

             // TODO(dkwingsmt): Only wrap Inkwell if onSort != null. Blocked by
             // https://github.com/flutter/flutter/issues/51152
             label = new InkWell(
-                onTap: () => onSort(),
+                onTap: () => onSort?.Invoke(),
                 child: label
             );
             return label;
                               !rows.Any((DataRow row) => row.onSelectChanged != null && !row.selected);
 
             List<TableColumnWidth> tableColumns =
-                new List<TableColumnWidth>(columns.Count + (displayCheckboxColumn ? 1 : 0));
-            List<TableRow> tableRows = Enumerable.Range(1, 10).Select((index) => {
+                new List<TableColumnWidth>(new TableColumnWidth[columns.Count + (displayCheckboxColumn ? 1 : 0)]);
+            
+            List<TableRow> tableRows = Enumerable.Range(0, rows.Count + 1).Select((index) => {
-                    children: new List<Widget>(tableColumns.Count)
+                    children: new List<Widget>(new Widget[tableColumns.Count])
-            // List<TableRow> tableRows = List<TableRow>.gegenerate(
-            //     rows.length + 1, // the +1 is for the header row
-            //     (int index) {
-            //     return TableRow(
-            //         key: index == 0 ? _headingRowKey : rows[index - 1].key,
-            //         decoration: index > 0 && rows[index - 1].selected
-            //             ? _kSelectedDecoration
-            //             : _kUnselectedDecoration,
-            //         children: List<Widget>(tableColumns.length),
-            //     );
-            // },
-            // );
 
             int rowIndex;
 
                     tableColumns[displayColumnIndex] = new IntrinsicColumnWidth();
                 }
 
+                var currentColumnIndex = dataColumnIndex;
                 tableRows[0].children[displayColumnIndex] = _buildHeadingCell(
                     context: context,
                     padding: padding,
                     onSort: column.onSort != null
-                        ? () => column.onSort(dataColumnIndex, sortColumnIndex != dataColumnIndex || !sortAscending)
+                        ? () => column.onSort(currentColumnIndex, sortColumnIndex != currentColumnIndex || !sortAscending)
                         : (VoidCallback) null,
                     sorted: dataColumnIndex == sortColumnIndex,
                     ascending: sortAscending
                     DataCell cell = row.cells[dataColumnIndex];
+                    var curRow = row;
                     tableRows[rowIndex].children[displayColumnIndex] = _buildDataCell(
                         context: context,
                         padding: padding,
                         showEditIcon: cell.showEditIcon,
                         onTap: cell.onTap,
                         onSelectChanged: () => {
-                            if (row.onSelectChanged != null) {
-                                row.onSelectChanged(!row.selected);
+                            if (curRow.onSelectChanged != null) {
+                                curRow.onSelectChanged(!curRow.selected);
                             }
                         });
                     rowIndex += 1;

com.unity.uiwidgets/Runtime/material/data_table_source.cs

     public abstract class DataTableSource : ChangeNotifier {
         public abstract DataRow getRow(int index);
 
-        public int rowCount { get; }
+        public virtual int rowCount { get; }
-        public bool isRowCountApproximate { get; }
+        public virtual bool isRowCountApproximate { get; }
-        public int selectedRowCount { get; }
+        public virtual int selectedRowCount { get; }
     }
 }

com.unity.uiwidgets/Runtime/material/dropdown.cs

                 ? material_._kAlignedMenuMargin
                 : material_._kUnalignedMenuMargin;
 
-            List<_MenuItem<T>> menuItems = new List<_MenuItem<T>>(widget.items.Count);
+            List<_MenuItem<T>> menuItems = new List<_MenuItem<T>>(new _MenuItem<T>[widget.items.Count]);
-                menuItems[index] = new _MenuItem<T>(
-                    item: widget.items[index],
+                var pindex = index;
+                menuItems[pindex] = new _MenuItem<T>(
+                    item: widget.items[pindex],
-                        _dropdownRoute.itemHeights[index] = size.height;
+                        _dropdownRoute.itemHeights[pindex] = size.height;
                     }
                 );
             }

com.unity.uiwidgets/Runtime/material/ink_decoration.cs

             VoidCallback onRemoved = null
         ) : base(controller: controller, referenceBox: referenceBox, onRemoved: onRemoved) {
             D.assert(configuration != null);
-            D.assert(decoration != null);
             D.assert(controller != null);
             D.assert(referenceBox != null);
             _configuration = configuration;

com.unity.uiwidgets/Runtime/material/paginated_data_table.cs

             this.availableRowsPerPage = availableRowsPerPage;
             this.onRowsPerPageChanged = onRowsPerPageChanged;
             this.dragStartBehavior = dragStartBehavior;
+            this.source = source;
         }
 
 

com.unity.uiwidgets/Runtime/widgets/routes.cs

         public _ModalScope(
             Key key = null, 
             ModalRoute<T> route = null) 
-            : base(key) {
+            : base(key, route) {
             this.route = route;
         }
 

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