[Widget] Add Cupertino ActivityIndicator Widget

Runtime/cupertino/button.cs

 using System;
-using RSG;
 using Unity.UIWidgets.animation;
 using Unity.UIWidgets.foundation;
 using Unity.UIWidgets.gestures;

Runtime/cupertino/slider.cs

             this._divisions = divisions;
             this._activeColor = activeColor;
             this._onChanged = onChanged;
+            this.onChangeStart = onChangeStart;
+            this.onChangeEnd = onChangeEnd;
             this._drag = new HorizontalDragGestureRecognizer();
             this._drag.onStart = this._handleDragStart;
             this._drag.onUpdate = this._handleDragUpdate;

Runtime/cupertino/activity_indicator.cs

+using System;
+using Unity.UIWidgets.animation;
+using Unity.UIWidgets.foundation;
+using Unity.UIWidgets.ui;
+using Unity.UIWidgets.widgets;
+using UnityEngine;
+using Canvas = Unity.UIWidgets.ui.Canvas;
+using Color = Unity.UIWidgets.ui.Color;
+
+namespace Unity.UIWidgets.cupertino {
+    static class CupertinoActivityIndicatorUtils {
+        public const float _kDefaultIndicatorRadius = 10.0f;
+        public const float _kTwoPI = Mathf.PI * 2.0f;
+        public const int _kTickCount = 12;
+        public const int _kHalfTickCount = _kTickCount / 2;
+        public static readonly Color _kTickColor = CupertinoColors.lightBackgroundGray;
+        public static readonly Color _kActiveTickColor = new Color(0xFF9D9D9D);
+    }
+
+    public class CupertinoActivityIndicator : StatefulWidget {
+        public CupertinoActivityIndicator(
+            Key key = null,
+            bool animating = true,
+            float radius = CupertinoActivityIndicatorUtils._kDefaultIndicatorRadius
+        ) : base(key: key) {
+            D.assert(radius > 0);
+            this.animating = animating;
+            this.radius = radius;
+        }
+
+        public readonly bool animating;
+        public readonly float radius;
+
+        public override State createState() {
+            return new _CupertinoActivityIndicatorState();
+        }
+    }
+
+    class _CupertinoActivityIndicatorState : TickerProviderStateMixin<CupertinoActivityIndicator> {
+        AnimationController _controller;
+
+        public override void initState() {
+            base.initState();
+            this._controller = new AnimationController(
+                duration: TimeSpan.FromSeconds(1),
+                vsync: this
+            );
+
+            if (this.widget.animating) {
+                this._controller.repeat();
+            }
+        }
+
+        public override void didUpdateWidget(StatefulWidget oldWidget) {
+            base.didUpdateWidget(oldWidget: oldWidget);
+            if (oldWidget is CupertinoActivityIndicator _oldWidget) {
+                if (this.widget.animating != _oldWidget.animating) {
+                    if (this.widget.animating) {
+                        this._controller.repeat();
+                    }
+                    else {
+                        this._controller.stop();
+                    }
+                }
+            }
+        }
+
+        public override void dispose() {
+            this._controller.dispose();
+            base.dispose();
+        }
+
+        public override Widget build(BuildContext context) {
+            return new SizedBox(
+                height: this.widget.radius * 2,
+                width: this.widget.radius * 2,
+                child: new CustomPaint(
+                    painter: new _CupertinoActivityIndicatorPainter(
+                        position: this._controller,
+                        radius: this.widget.radius
+                    )
+                )
+            );
+        }
+    }
+
+    class _CupertinoActivityIndicatorPainter : AbstractCustomPainter {
+        public _CupertinoActivityIndicatorPainter(
+            Animation<float> position,
+            float radius
+        ) : base(repaint: position) {
+            this.tickFundamentalRRect = RRect.fromLTRBXY(
+                left: -radius,
+                top: 1.0f * radius / CupertinoActivityIndicatorUtils._kDefaultIndicatorRadius,
+                right: -radius / 2.0f,
+                bottom: -1.0f * radius / CupertinoActivityIndicatorUtils._kDefaultIndicatorRadius,
+                radiusX: 1.0f,
+                radiusY: 1.0f
+            );
+            this.position = position;
+        }
+
+        readonly Animation<float> position;
+        readonly RRect tickFundamentalRRect;
+
+        public override void paint(Canvas canvas, Size size) {
+            Paint paint = new Paint();
+
+            canvas.save();
+            canvas.translate(size.width / 2.0f, size.height / 2.0f);
+
+            int activeTick = (CupertinoActivityIndicatorUtils._kTickCount * this.position.value).floor();
+
+            for (int i = 0; i < CupertinoActivityIndicatorUtils._kTickCount; ++i) {
+                float t = (((i + activeTick) % CupertinoActivityIndicatorUtils._kTickCount) /
+                           CupertinoActivityIndicatorUtils._kHalfTickCount).clamp(0, 1);
+                paint.color = Color.lerp(a: CupertinoActivityIndicatorUtils._kActiveTickColor,
+                    b: CupertinoActivityIndicatorUtils._kTickColor, t: t);
+                canvas.drawRRect(rect: this.tickFundamentalRRect, paint: paint);
+                canvas.rotate(-CupertinoActivityIndicatorUtils._kTwoPI / CupertinoActivityIndicatorUtils._kTickCount);
+            }
+
+            canvas.restore();
+        }
+
+        public override bool shouldRepaint(CustomPainter oldPainter) {
+            return (oldPainter as _CupertinoActivityIndicatorPainter).position != this.position;
+        }
+    }
+}

Runtime/cupertino/activity_indicator.cs.meta

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