Fix some issues. Add samples.

Author: Yuncong Zhang

Runtime/material/app.cs

@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using Unity.UIWidgets.animation;
 using Unity.UIWidgets.foundation;
+using Unity.UIWidgets.service;
 using Unity.UIWidgets.ui;
 using Unity.UIWidgets.widgets;
 using TextStyle = Unity.UIWidgets.painting.TextStyle;
@@ -158,14 +159,25 @@ public override Widget build(BuildContext context) {
                 initialRoute: this.widget.initialRoute,
                 onGenerateRoute: this.widget.onGenerateRoute,
                 onUnknownRoute: this.widget.onUnknownRoute,
-                builder: (BuildContext congtext, Widget child) => {
-                    ThemeData theme = this.widget.theme ?? ThemeData.fallback();
+                builder: (BuildContext _context, Widget child) => {
+                    ThemeData theme;
+                    Brightness platformBrightness = MediaQuery.platformBrightnessOf(_context);
+                    if (platformBrightness == Brightness.dark && this.widget.darkTheme != null) {
+                        theme = this.widget.darkTheme;
+                    }
+                    else if (this.widget.theme != null) {
+                        theme = this.widget.theme;
+                    }
+                    else {
+                        theme = ThemeData.fallback();
+                    }
+
                     return new AnimatedTheme(
                         data: theme,
                         isMaterialAppTheme: true,
                         child: this.widget.builder != null
                             ? new Builder(
-                                builder: (_context) => { return this.widget.builder(_context, child); }
+                                builder: (__context) => { return this.widget.builder(__context, child); }
                             )
                             : child
                     );

Runtime/material/bottom_app_bar_theme.cs

@@ -10,6 +10,9 @@ public BottomAppBarTheme(
             float? elevation = null,
             NotchedShape shape = null
         ) {
+            this.color = color;
+            this.elevation = elevation;
+            this.shape = shape;
         }
 
         public readonly Color color;

Samples/UIWidgetSample/LongPressSample.cs

@@ -0,0 +1,45 @@
+using Unity.UIWidgets.animation;
+using Unity.UIWidgets.engine;
+using Unity.UIWidgets.material;
+using Unity.UIWidgets.widgets;
+using UnityEngine;
+
+namespace UIWidgetsSample {
+    public class LongPressSample: UIWidgetsSamplePanel {
+        
+        protected override Widget createWidget()  {
+            return new WidgetsApp(
+                home: new LongPressSampleWidget(),
+                pageRouteBuilder: this.pageRouteBuilder);
+        }
+    }
+
+    public class LongPressSampleWidget: StatefulWidget {
+        public override State createState() {
+            return new _LongPressSampleWidgetState();
+        }
+    }
+
+    class _LongPressSampleWidgetState : State<LongPressSampleWidget> {
+        public override Widget build(BuildContext context) {
+            return new GestureDetector(
+                onLongPressDragStart: (value) => {
+                    Debug.Log($"Long Press Drag Start: {value}");
+                },
+                onLongPressDragUpdate: (value) => {
+                    Debug.Log($"Long Press Drag Update: {value}");
+                },
+                onLongPressDragUp: (value) => {
+                    Debug.Log($"Long Press Drag Up: {value}");
+                },
+                child: new Center(
+                    child: new Container(
+                        width: 200,
+                        height: 200,
+                        color: Colors.blue
+                    )
+                )
+            );
+        }
+    }
+}