[Cupertino] Fix bugs.

Runtime/cupertino/app.cs

             List<Locale> supportedLocales = null,
             bool showPerformanceOverlay = false
         ) : base(key: key) {
-            // D.assert(routes != null);
-            // D.assert(navigatorObservers != null);
-            // D.assert(title != null);
-            // D.assert(showPerformanceOverlay != null);
+            D.assert(title != null);
 
             supportedLocales = supportedLocales ?? new List<Locale> {new Locale("en", "US")};
             this.navigatorKey = navigatorKey;

Runtime/cupertino/bottom_app_bar.cs

                 () => "Tabs need at least 2 items to conform to Apple's HIG"
             );
             D.assert(0 <= currentIndex && currentIndex < items.Count);
-            D.assert(inactiveColor != null);
+            
+
             this.items = items;
             this.onTap = onTap;
             this.currentIndex = currentIndex;
 
             for (int index = 0; index < this.items.Count; index += 1) {
                 bool active = index == this.currentIndex;
+                var tabIndex = index;
                 result.Add(
                     this._wrapActiveItem(
                         context,
-                                onTap: this.onTap == null ? null : (GestureTapCallback) (() => { this.onTap(index); }),
+                                onTap: this.onTap == null ? null : (GestureTapCallback) (() => { this.onTap(tabIndex); }),
                                 child: new Padding(
                                     padding: EdgeInsets.only(bottom: 4.0f),
                                     child: new Column(

Runtime/cupertino/slider.cs

         public override void updateRenderObject(BuildContext context, RenderObject _renderObject) {
             _RenderCupertinoSlider renderObject = _renderObject as _RenderCupertinoSlider;
             renderObject.value = this.value ?? 0.0f;
-            renderObject.divisions = this.divisions ?? 0;
+            renderObject.divisions = this.divisions;
             renderObject.activeColor = this.activeColor;
             renderObject.onChanged = this.onChanged;
             renderObject.onChangeStart = this.onChangeStart;

Runtime/cupertino/tab_scaffold.cs

         public override void initState() {
             base.initState();
             this._currentPage = this.widget.tabBar.currentIndex;
+            
         }
 
         public override void didUpdateWidget(StatefulWidget _oldWidget) {
         public override void initState() {
             base.initState();
             this.tabs = new List<Widget>(this.widget.tabNumber);
+            for (int i = 0; i < this.widget.tabNumber; i++) {
+                this.tabs.Add(null);
+            }
             this.tabFocusNodes = Enumerable.Repeat(new FocusScopeNode(), this.widget.tabNumber).ToList();
         }
 
             for (int index = 0; index < this.widget.tabNumber; index++) {
                 bool active = index == this.widget.currentTabIndex;
 
+                var tabIndex = index;
-                    this.tabs[index] = this.widget.tabBuilder(context, index);
+                    this.tabs[index] = this.widget.tabBuilder(context, tabIndex);
                 }
 
                 children.Add(new Offstage(

Samples/UIWidgetsGallery/demo/cupertino/cupertino_alert_demo.cs

                                             }
                                         ),
                                         // TODO: FIX BUG
-                                        // new Padding(padding: EdgeInsets.all(8.0f)),
-                                        // CupertinoButton.filled(
-                                        //     child: new Text("Action Sheet"),
-                                        //     padding: EdgeInsets.symmetric(vertical: 16.0f, horizontal: 36.0f),
-                                        //     onPressed: () => {
-                                        //         this.showDemoActionSheet(
-                                        //             context: _context,
-                                        //             child: new CupertinoActionSheet(
-                                        //                 title: new Text("Favorite Dessert"),
-                                        //                 message: new Text(
-                                        //                     "Please select the best dessert from the options below."),
-                                        //                 actions: new List<Widget> {
-                                        //                     new CupertinoActionSheetAction(
-                                        //                         child: new Text("Profiteroles"),
-                                        //                         onPressed: () => {
-                                        //                             Navigator.pop(_context, "Profiteroles");
-                                        //                         }
-                                        //                     ),
-                                        //                     new CupertinoActionSheetAction(
-                                        //                         child: new Text("Cannolis"),
-                                        //                         onPressed: () => {
-                                        //                             Navigator.pop(_context, "Cannolis");
-                                        //                         }
-                                        //                     ),
-                                        //                     new CupertinoActionSheetAction(
-                                        //                         child: new Text("Trifle"),
-                                        //                         onPressed: () => { Navigator.pop(_context, "Trifle"); }
-                                        //                     )
-                                        //                 },
-                                        //                 cancelButton: new CupertinoActionSheetAction(
-                                        //                     child: new Text("Cancel"),
-                                        //                     isDefaultAction: true,
-                                        //                     onPressed: () => { Navigator.pop(_context, "Cancel"); }
-                                        //                 )
-                                        //             )
-                                        //         );
-                                        //     }
-                                        // )
+                                        new Padding(padding: EdgeInsets.all(8.0f)),
+                                        CupertinoButton.filled(
+                                            child: new Text("Action Sheet"),
+                                            padding: EdgeInsets.symmetric(vertical: 16.0f, horizontal: 36.0f),
+                                            onPressed: () => {
+                                                this.showDemoActionSheet(
+                                                    context: _context,
+                                                    child: new CupertinoActionSheet(
+                                                        title: new Text("Favorite Dessert"),
+                                                        message: new Text(
+                                                            "Please select the best dessert from the options below."),
+                                                        actions: new List<Widget> {
+                                                            // new CupertinoActionSheetAction(
+                                                            //     child: new Text("Profiteroles"),
+                                                            //     onPressed: () => {
+                                                            //         Navigator.pop(_context, "Profiteroles");
+                                                            //     }
+                                                            // ),
+                                                            // new CupertinoActionSheetAction(
+                                                            //     child: new Text("Cannolis"),
+                                                            //     onPressed: () => {
+                                                            //         Navigator.pop(_context, "Cannolis");
+                                                            //     }
+                                                            // ),
+                                                            // new CupertinoActionSheetAction(
+                                                            //     child: new Text("Trifle"),
+                                                            //     onPressed: () => { Navigator.pop(_context, "Trifle"); }
+                                                            // )
+                                                        },
+                                                        cancelButton: new CupertinoActionSheetAction(
+                                                            child: new Text("Cancel"),
+                                                            isDefaultAction: true,
+                                                            onPressed: () => { Navigator.pop(_context, "Cancel"); }
+                                                        )
+                                                    )
+                                                );
+                                            }
+                                        )
                                     }
                                 )
                             };

Samples/UIWidgetsGallery/demo/cupertino/cupertino_slider_demo.cs

                             child: new Column(
                                 mainAxisAlignment: MainAxisAlignment.spaceAround,
                                 children: new List<Widget> {
-                                    // TODO: FIX BUG
-                                    // new Column(
-                                    //     mainAxisSize: MainAxisSize.min,
-                                    //     children: new List<Widget> {
-                                    //         new CupertinoSlider(
-                                    //             value: this._value,
-                                    //             min: 0.0f,
-                                    //             max: 100.0f,
-                                    //             onChanged: (float value) => {
-                                    //                 this.setState(() => { this._value = value; });
-                                    //             }
-                                    //         ),
-                                    //         new Text($"Cupertino Continuous: {this._value.ToString("F1")}"),
-                                    //     }
-                                    // ),
+                                    new Column(
+                                        mainAxisSize: MainAxisSize.min,
+                                        children: new List<Widget> {
+                                            new CupertinoSlider(
+                                                value: this._value,
+                                                min: 0.0f,
+                                                max: 100.0f,
+                                                onChanged: (float value) => {
+                                                    this.setState(() => { this._value = value; });
+                                                }
+                                            ),
+                                            new Text($"Cupertino Continuous: {this._value.ToString("F1")}"),
+                                        }
+                                    ),
                                     new Column(
                                         mainAxisSize: MainAxisSize.min,
                                         children: new List<Widget> {

Samples/UIWidgetsGallery/gallery/demos.cs

                 // new GalleryDemo(
                 //     title: "Navigation",
                 //     icon: GalleryIcons.bottom_navigation,
-                //     category: GalleryDemoCategory._kCupertinoComponents,
+                //     category: _kCupertinoComponents,
-                //     buildRoute: (BuildContext context) => CupertinoNavigationDemo()
+                //     buildRoute: (BuildContext context) => new CupertinoNavigationDemo()
                 // ),
                 // new GalleryDemo(
                 //     title: "Pickers",