Fix some issues.

Runtime/material/outline_button.cs

                     }
                 )
             ) {
-            D.assert(onPressed != null);
             D.assert(highlightElevation == null || highlightElevation >= 0.0f);
             D.assert(icon != null);
             D.assert(label != null);
         ) : base(key: key) {
             D.assert(highlightElevation != null && highlightElevation >= 0.0f);
             D.assert(highlightedBorderColor != null);
-            D.assert(this.onPressed != null);
             this.onPressed = onPressed;
             this.brightness = brightness;
             this.textTheme = textTheme;

Runtime/material/tabs.cs

 
             int tabCount = this.widget.tabs.Count;
             for (int index = 0; index < tabCount; index++) {
+                int tabIndex = index;
-                    onTap: () => { this._handleTap(index); },
+                    onTap: () => { this._handleTap(tabIndex); },
                     child: new Padding(
                         padding: EdgeInsets.only(bottom: this.widget.indicatorWeight),
                         child: wrappedTabs[index]

Samples/UIWidgetsGallery/gallery/demo.cs

         string _exampleCode;
 
         public override void didChangeDependencies() {
-            new ExampleCodeParser().getExampleCode(this.widget.exampleCodeTag, DefaultAssetBundle.of(this.context)).Then(
-                (string code) => {
-                    if (this.mounted) {
-                        this.setState(() => { this._exampleCode = code ?? "Example code not found"; });
-                    }
-                });
+            string code = new ExampleCodeParser().getExampleCode(this.widget.exampleCodeTag, DefaultAssetBundle.of(this.context));
+            if (this.mounted) {
+                this.setState(() => { this._exampleCode = code; });
+            }
         }
 
         public override Widget build(BuildContext context) {

Samples/UIWidgetsGallery/gallery/example_code_parser.cs

 using System.Linq;
 using System.Threading.Tasks;
 using RSG;
+using Unity.UIWidgets.foundation;
 using UnityEngine;
 
 namespace UIWidgetsGallery.gallery {
     
         Dictionary<string, string> _exampleCode;
     
-        public IPromise<string> getExampleCode(string tag, AssetBundle bundle) {
+        public string getExampleCode(string tag, AssetBundle bundle) {
-            return Promise<string>.Resolved(this._exampleCode[tag]);
+            return this._exampleCode.getOrDefault(tag);
-        async Task _parseExampleCode(AssetBundle bundle) {
+        void _parseExampleCode(AssetBundle bundle) {
             string code = Resources.Load<TextAsset>("example_code.cs")?.text ??
                                 "// example_code.cs not found\n";
             this._exampleCode = new Dictionary<string, string>{};
     
             foreach (string line in lines) {
                 if (codeBlock == null) {
-                    // Outside a block.
-                        // Starting a new code block.
-                        // Just skipping the line.
-                    // Inside a block.
-                        // Add the block.
-                        // Add to the current block
-                        // trimRight() to remove any \r on Windows
-                        // without removing any useful indentation
                         codeBlock.Add(line.TrimEnd());
                     }
                 }

Samples/UIWidgetsGallery/gallery/home.cs

     }
 
     class _GalleryHomeState : SingleTickerProviderStateMixin<GalleryHome> {
-        static readonly GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>.key();
+        readonly GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>.key();
         AnimationController _controller;
         GalleryDemoCategory _category;
 

Samples/UIWidgetsGallery/gallery/syntax_highlighter.cs

     public class DartSyntaxHighlighter : SyntaxHighlighter {
         public DartSyntaxHighlighter(SyntaxHighlighterStyle _style = null) {
             this._spans = new List<_HighlightSpan> { };
-            this._style = this._style ?? SyntaxHighlighterStyle.darkThemeStyle();
+            this._style = _style ?? SyntaxHighlighterStyle.darkThemeStyle();
         }
 
         SyntaxHighlighterStyle _style;
             this._scanner = new StringScanner(this._src);
 
             if (this._generateSpans()) {
-                // Successfully parsed the code
                 List<TextSpan> formattedText = new List<TextSpan> { };
                 int currentPosition = 0;
 
                 return new TextSpan(style: this._style.baseStyle, children: formattedText);
             }
             else {
-                // Parsing failed, return with only basic formatting
                 return new TextSpan(style: this._style.baseStyle, text: src);
             }
         }
 
             while (!this._scanner.isDone) {
-                // Skip White space
                 this._scanner.scan(new Regex(@"\s+"));
 
                 // Block comments