TL; DR：当前的 UIWidgets 代码仓库是否存在性能问题？如果是的话，未来大概什么时候会优化？

最近尝试学习 UIWidgets，发现自己写的示例 app 即使非常简单，也会有非常肉眼可见的性能问题，比如说： 1）用 PageView 切换页面时很卡 2）Switch Widgets 的动画很卡

用 graphy 看了看，确实在上述两种场景下 fps 会掉得特别厉害 由于在 Editor 上能流畅运行，一开始觉得是自己测试机性能太差，但【ConnectApp】是能流畅运行的，所以怀疑是实现的问题 上网查了查，用上了一些常用的小优化，问题没有得到解决 后面把官方的【Gallery】打包下来试了试，发现【性能问题更加严重】，所以又怀疑是这边的 UIWidgets 并不是最新版、又或是直接用 unity 打包本身会存在性能问题 看了看 issue，有提到动态 fps，有提到未来会把 ConnectApp 那边的功能迁移过来，所以我这边也不好判断到底是我写拐了还是说当前的 UIWidgets 尚未成熟 所以就回到抬头的问题了：当前的 UIWidgets 代码仓库是否存在性能问题？如果是的话，未来大概什么时候会优化？

使用 Packages\com.unity.uiwidgets\Samples\UIWidgetSample\TextInput.unity 场景输出到安卓机上运行，打开部分页面会报如下错误： 2019-10-18 15:07:12.389 8937-8955/? E/Unity: AssertionError: Error caught by scheduler library, thrown during a scheduler callback. unmatched save/restore commands at Unity.UIWidgets.ui.uiPictureRecorder.endRecording () [0x0000e] in :0 at Unity.UIWidgets.ui.CommandBufferCanvas.flush () [0x00000] in :0 at Unity.UIWidgets.editor.WindowSurfaceImpl._presentSurface (Unity.UIWidgets.ui.Canvas canvas) [0x00010] in :0 at Unity.UIWidgets.editor.WindowSurfaceImpl.b__9_0 (Unity.UIWidgets.editor.SurfaceFrame frame, Unity.UIWidgets.ui.Canvas canvas) [0x00000] in :0 at Unity.UIWidgets.editor.SurfaceFrame._performSubmit () [0x00017] in :0 at Unity.UIWidgets.editor.SurfaceFrame.submit () [0x0000a] in :0 at Unity.UIWidgets.editor.Rasterizer._drawToSurface (Unity.UIWidgets.flow.LayerTree layerTree) [0x0004e] in <d683ce45a0b6415ca62a1b21 issue01.txt

NullReferenceException: Object reference not set to an instance of an object
Unity.UIWidgets.scheduler.SchedulerBinding.scheduleFrame () (at Packages/com.unity.uiwidgets/Runtime/scheduler/binding.cs:184)
Unity.UIWidgets.scheduler.SchedulerBinding.ensureVisualUpdate () (at Packages/com.unity.uiwidgets/Runtime/scheduler/binding.cs:162)
Unity.UIWidgets.widgets.WidgetsBinding._handleBuildScheduled () (at Packages/com.unity.uiwidgets/Runtime/widgets/binding.cs:108)
Unity.UIWidgets.widgets.BuildOwner.scheduleBuildFor (Unity.UIWidgets.widgets.Element element) (at Packages/com.unity.uiwidgets/Runtime/widgets/framework.cs:891)
Unity.UIWidgets.widgets.Element.markNeedsBuild () (at Packages/com.unity.uiwidgets/Runtime/widgets/framework.cs:2044)
Unity.UIWidgets.widgets.State.setState (Unity.UIWidgets.ui.VoidCallback fn) (at Packages/com.unity.uiwidgets/Runtime/widgets/framework.cs:510)
BookListState.<RequestBooks>b__2_0 (System.Object response) (at Assets/Scripts/BookListPage.cs:45)
HTTPHelper+<GetAsync>d__8`1[T].MoveNext () (at Assets/Scripts/HTTPHelper.cs:82)
--- End of stack trace from previous location where exception was thrown ---
System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () (at <d7ac571ca2d04b2f981d0d886fa067cf>:0)
System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__6_0 (System.Object state) (at <d7ac571ca2d04b2f981d0d886fa067cf>:0)
UnityEngine.UnitySynchronizationContext+WorkRequest.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnitySynchronizationContext.cs:115)
UnityEngine.UnitySynchronizationContext:ExecuteTasks()

用 HTTPClient 异步发 Get 请求，在回调函数中 setState 报上面的错误。 具体仓库在 UIWidget-Practice，报错行数在 这里。

还是说我写的姿势不对？

Listener的onPointerEnter和onPointerExit触发时报错。 代码如下：

public abstract class AUIWidgetsPanel : UIWidgetsPanel, ICanvasRaycastFilter
    {
        public abstract Widget Home { get; }

        private Texture2D texture2D;
        private int width;
        private int height;
        private Vector2 local;
        private Rect rect;

        protected override void OnEnable()
        {
            base.OnEnable();
            UpdateSize();
        }

        private void UpdateSize()
        {
            RectTransform rectTransform = this.GetComponent<RectTransform>();
            int newWidth = (int)rectTransform.rect.width;
            int newHeight = (int)rectTransform.rect.height;

            if (this.width != newWidth || this.height != newHeight)
            {
                this.width = newWidth;
                this.height = newHeight;

                this.texture2D = new Texture2D(this.width, this.height, TextureFormat.RGBA32, false);
            }
        }

        protected override void OnRectTransformDimensionsChange()
        {
            base.OnRectTransformDimensionsChange();
            UpdateSize();
        }

        public bool IsRaycastLocationValid(Vector2 sp, Camera eventCamera)
        {
            if (!this.isActiveAndEnabled)
            {
                return true;
            }

            RectTransformUtility.ScreenPointToLocalPointInRectangle(this.rectTransform, sp, eventCamera, out local);
            rect = this.rectTransform.rect;
            local.x += this.rectTransform.pivot.x * rect.width;
            local.y += this.rectTransform.pivot.y * rect.height;
            uvRect = this.uvRect;
            float u = local.x / rect.width * uvRect.width + uvRect.x;
            float v = local.y / rect.height * uvRect.height + uvRect.y;

            RenderTexture.active = this.texture as RenderTexture;
            texture2D.ReadPixels(new Rect(0, 0, this.width, this.height), 0, 0);
            texture2D.Apply();

            return texture2D.GetPixelBilinear(u, v).a != 0;
        }

        protected override Widget createWidget()
        {
            return new MaterialApp(
                home: this.Home
                );
        }
    }

public class PenItem : AUIWidgetsPanel
    {
        public bool IsSelected;

        public override Widget Home => new PenItemWidget(this);

        public PenItem Reduce(PenItem state, object action)
        {
            if (action is bool selected)
            {
                state.IsSelected = selected;
            }
            return state;
        }
    }

    public class PenItemWidget : StatelessWidget
    {
        private Store<PenItem> store;

        public PenItemWidget(PenItem panel)
        {
            this.store = new Store<PenItem>(panel.Reduce, panel);
        }

        public override Widget build(BuildContext context)
        {
            return new ScreenAdapter(
                context: context,
                child: new StoreProvider<PenItem>(
                    store: this.store,
                    child: new StoreConnector<PenItem, bool>(
                        converter: state => state.IsSelected,
                        builder: (builderContext, value, dispatcher) => build(builderContext, value, dispatcher)
                        )
                    )
                );
        }

        public Widget build(BuildContext context, bool state, Dispatcher dispatcher)
        {
            return new Stack(
                children: new List<Widget>
                {
                    new Listener(
                        behavior: Unity.UIWidgets.rendering.HitTestBehavior.opaque,
                        child:new Container(
                            alignment:Alignment.bottomCenter,
                            child:AddressableAssetImage.addressable(Address.UISprite_电压表笔_黑)
                            ),
                        onPointerEnter:_ => dispatcher.dispatch(true),
                        onPointerExit:_ => dispatcher.dispatch(false)
                        ),
                    new Align(
                        alignment:Alignment.bottomCenter,
                        child:AddressableAssetImage.addressable(state ? Address.UISprite_电压表笔_light_select : Address.UISprite_电压表笔_light_normal)
                        ),
                }
                );
        }
    }

运行报错截图：

详细报错信息： AssertionError: Error caught by widgets library, thrown while rebuilding dirty elements. The element being rebuilt at the time was index 0 of 1: Unity.UIWidgets.Redux._StoreListener2[ETModel.PenItem,System.Boolean](state:Unity.UIWidgets.Redux._StoreListenerState2[ETModel.PenItem,System.Boolean]#D3E00) at Unity.UIWidgets.widgets.Element.rebuild () [0x000a2] in E:\RD-NE19042\Unity\Library\PackageCache\[email protected]\Runtime\widgets\framework.cs:2085 at Unity.UIWidgets.widgets.BuildOwner.buildScope (Unity.UIWidgets.widgets.Element context, Unity.UIWidgets.ui.VoidCallback callback) [0x001b9] in E:\RD-NE19042\Unity\Library\PackageCache\[email protected]\Runtime\widgets\framework.cs:997 Unity.UIWidgets.widgets.Element.rebuild () (at Library/PackageCache/[email protected]/Runtime/widgets/framework.cs:2085) Unity.UIWidgets.widgets.BuildOwner.buildScope (Unity.UIWidgets.widgets.Element context, Unity.UIWidgets.ui.VoidCallback callback) (at Library/PackageCache/[email protected]/Runtime/widgets/framework.cs:997) UnityEngine.Debug:LogException(Exception) Unity.UIWidgets.foundation.D:logError(String, Exception) (at Library/PackageCache/[email protected]/Runtime/foundation/debug.cs:15) Unity.UIWidgets.foundation.UIWidgetsError:dumpErrorToConsole(UIWidgetsErrorDetails, Boolean) (at Library/PackageCache/[email protected]/Runtime/foundation/assertions.cs:120) Unity.UIWidgets.foundation.UIWidgetsError:dumpErrorToConsole(UIWidgetsErrorDetails) (at Library/PackageCache/[email protected]/Runtime/foundation/assertions.cs:105) Unity.UIWidgets.foundation.UIWidgetsError:reportError(UIWidgetsErrorDetails) (at Library/PackageCache/[email protected]/Runtime/foundation/assertions.cs:131) Unity.UIWidgets.widgets.WidgetsD:_debugReportException(String, Exception, InformationCollector) (at Library/PackageCache/[email protected]/Runtime/widgets/debug.cs:140) Unity.UIWidgets.widgets.BuildOwner:buildScope(Element, VoidCallback) (at Library/PackageCache/[email protected]/Runtime/widgets/framework.cs:1000) Unity.UIWidgets.widgets.WidgetsBinding:drawFrame() (at Library/PackageCache/[email protected]/Runtime/widgets/binding.cs:150) Unity.UIWidgets.rendering.RendererBinding:_handlePersistentFrameCallback(TimeSpan) (at Library/PackageCache/[email protected]/Runtime/rendering/binding.cs:73) Unity.UIWidgets.scheduler.SchedulerBinding:_invokeFrameCallback(FrameCallback, TimeSpan, String) (at Library/PackageCache/[email protected]/Runtime/scheduler/binding.cs:356) Unity.UIWidgets.scheduler.SchedulerBinding:handleDrawFrame() (at Library/PackageCache/[email protected]/Runtime/scheduler/binding.cs:297) Unity.UIWidgets.scheduler.SchedulerBinding:_handleDrawFrame() (at Library/PackageCache/[email protected]/Runtime/scheduler/binding.cs:234) Unity.UIWidgets.editor.WindowAdapter:_beginFrame() (at Library/PackageCache/[email protected]/Runtime/editor/editor_window.cs:330) Unity.UIWidgets.editor.WindowAdapter:_doOnGUI(Event) (at Library/PackageCache/[email protected]/Runtime/editor/editor_window.cs:338) Unity.UIWidgets.editor.WindowAdapter:OnGUI(Event) (at Library/PackageCache/[email protected]/Runtime/editor/editor_window.cs:307) Unity.UIWidgets.engine.UIWidgetWindowAdapter:OnGUI(Event) (at Library/PackageCache/[email protected]/Runtime/engine/UIWidgetsPanel.cs:54) Unity.UIWidgets.engine.UIWidgetsPanel:Update() (at Library/PackageCache/[email protected]/Runtime/engine/UIWidgetsPanel.cs:231)

新建了一个TextField 只要点击输入框就会报错

public class UIChatScreen : StatefulWidget
{
    public override State createState()
    {
        return new ChatScreen();
    }
}

public class ChatScreen : State<StatefulWidget>
{

    TextEditingController controller = new TextEditingController();
    FocusNode _focusNode = new FocusNode();
    public override void initState()
    {
        base.initState();

        _focusNode.addListener(focusListener);
    }

    void focusListener()
    {
        UnityEngine.Debug.LogError(_focusNode.hasFocus);
    }

    public override Widget build(BuildContext context)
    {
        return new Container(
            width: 550f,
            height:50,
            alignment:Alignment.center,
            child: new TextField(
                focusNode: _focusNode,
                style: new TextStyle(
                    color: Color.fromARGB(255, 255, 238, 204),
                    fontSize: 20,
                    decoration: TextDecoration.none,
                    fontWeight: FontWeight.normal
                    ),
                controller: controller
                )
            );
    }
}

Hi! Wrong scale and wrong drawing, I repeated the example https://www.youtube.com/watch?v=5KbiU-93-yU , but the display is not correct, everything is small, the buttons have a rounding wrong, the picture in the favorite item is also not correct drawn

Bug Video: https://monosnap.com/file/H87LBr2xudui0tKENfmtHhFsI1rBR9

Unity 2019.1 Unity Project: https://drive.google.com/open?id=1yUTlIVfLpGKG4QceutsUeTx-4SNWp39W Flutter Project: https://github.com/devefy/Flutter-Story-App-UI

在我将项目中的【Asset Store】版本的 UIWidgets，换成【master branch】 的版本并导入到 Packages 中后，发现在手机屏幕抬头处有较为明显的显示问题（【之前是不存在的】），且不同机型的这个显示问题表现还不一样：

• 红米 Note 8： 可以看到，抬头处有一些蓝色的颜色块

• 小米 Mix 2： 可以看到，抬头处有一些下面 UI 的影子；此外在程序运行过程中，抬头处会出现闪屏的现象

不知这是属于我的编码问题，还是属于兼容性问题？

在开发桌面应用过程中，全屏透明UI中边缘为按钮、清单等Widgets,中间部分属于透明UI，是否可以将透明部分的点击事件等穿透传递下去来达到点击场景物体的目的，目前思路是在UIWidgetsPanel的事件处理函数中检测当前点击位置的像素颜色，低于阈值则将事件传递下去，但是目前在获取其texture转为texture2D后像素点的颜色始终为0XCDCDCDCD,能否提供一些帮助？

Expected Behaviour

According to flutter/issues/13101, onScaleUpdate should report scale = 1.0 when there is only one pointer down on the screen, which also known as a pan or drag gesture.

Current Behaviour

In UIWidgetsPanel the GestureDetector works well. In UIWidgetsEditorWindow the GestureDetector reports a value that is not 1.0 when dragging around. (Unity 2018.4.0, macOS 10.14.5)

Test Script

using System;
using System.Collections.Generic;
using FinGameWorks.Scripts.Helpers;
using Unity.UIWidgets.foundation;
using Unity.UIWidgets.material;
using Unity.UIWidgets.painting;
using Unity.UIWidgets.ui;
using Unity.UIWidgets.widgets;
using UnityEngine;
using Transform = Unity.UIWidgets.widgets.Transform;

namespace FinGameWorks.Scripts.Views
{
    public class ScrollView : StatefulWidget
    {
        public readonly Widget child;
        public float MinScale;
        public float MaxScale;
        public float ContentSizeWidth;
        public float ContentSizeHeight;
        
        public ScrollView(Widget child, float minScale = 0.5f, float maxScale = 3.0f, float contentSizeWidth = 2000, float contentSizeHeight = 2000, Key key = null) : base(key)
        {
            this.child = child;
            MinScale = minScale;
            MaxScale = maxScale;
            ContentSizeWidth = contentSizeWidth;
            ContentSizeHeight = contentSizeHeight;
        }

        public override State createState()
        {
            return new ScrollViewState();
        }
    }

    public class ScrollViewState : SingleTickerProviderStateMixin<ScrollView>
    {
        public Offset Offset = Offset.zero;
        public float Scale = 1;
        public Offset MoveVelocity = Offset.zero;
        public GlobalKey ContentViewContainerKey = GlobalKey.key();

        private float aimedScale = 1;
        private Offset aimedOffset = Offset.zero;
//        private Offset scaleOrigin = Offset.zero;
        private Offset previousPointerPosition = Offset.zero;
        private TimeSpan previousTime = TimeSpan.Zero;
        private float previousScale = 1;
        
        public override void initState()
        {
            base.initState();
            WidgetsBinding.instance.scheduleFrameCallback(FrameCallback);
        }

        private void FrameCallback(TimeSpan dur)
        {
            setState(() =>
            {
//                Offset moveDampSpeed = Offset.zero;
//                Offset offsetDampSpeed = Offset.zero;
//                float scaleDampSpeed = 0;
                
//                MoveVelocity = MoveVelocity.DampTo(Offset.zero, ref moveDampSpeed, 0.5f);
//                aimedOffset += MoveVelocity / (1000.0f / (dur - previousTime).Milliseconds);
//                Offset = Offset.DampTo(aimedOffset, ref offsetDampSpeed,0.15f);
//                Scale = Mathf.SmoothDamp(Scale, aimedScale, ref scaleDampSpeed, 0.2f);
//                Scale = Mathf.Max(widget.MinScale, Scale);
//                Scale = Mathf.Min(widget.MaxScale, Scale);
//                float scaleDiff = Scale - previousScale;
//                aimedOffset -= (scaleOrigin - aimedOffset) * scaleDiff;
                
//                previousTime = dur;
//                previousScale = Scale;
            });
            WidgetsBinding.instance.scheduleFrameCallback(FrameCallback);
        }
        
        public override Widget build(BuildContext context)
        {
            return new GestureDetector
            (
                onScaleStart: details =>
                {
                },
                onScaleUpdate: details =>
                {
//                    MoveVelocity = Offset.zero;
                    
                    float scaleDiff = previousScale * (details.scale - 1);
                    if (aimedScale >= widget.MaxScale && scaleDiff > 0)
                    {
                        scaleDiff = 0;
                    }
                    if (aimedScale <= widget.MinScale && scaleDiff < 0)
                    {
                        scaleDiff = 0;
                    }
                    aimedScale += scaleDiff;
                    aimedScale = Mathf.Max(widget.MinScale, aimedScale);
                    aimedScale = Mathf.Min(widget.MaxScale, aimedScale);
                    
                    Offset scaleOffsetDiff = (aimedOffset - previousPointerPosition) * (scaleDiff / aimedScale);
                    aimedOffset += scaleOffsetDiff;
                    previousScale = details.scale;
                    Debug.Log("scaleDiff = " + scaleDiff);
                },
                onScaleEnd: details =>
                {
//                    MoveVelocity = details.velocity.pixelsPerSecond;
                },
                child: new Listener
                (
                    onPointerDown: evt =>
                    {
                        previousPointerPosition = evt.position;
                    }, 
                    onPointerMove: evt =>
                    {
                        aimedOffset += evt.delta;
                        previousPointerPosition = evt.position;
                    },
                    onPointerScroll: evt =>
                    {
                        float scaleDiff = evt.delta.dy / MediaQuery.of(context).size.height;
                        if (aimedScale >= widget.MaxScale && scaleDiff > 0)
                        {
                            scaleDiff = 0;
                        }
                        if (aimedScale <= widget.MinScale && scaleDiff < 0)
                        {
                            scaleDiff = 0;
                        }
                        aimedOffset += (aimedOffset - evt.position) * (scaleDiff / aimedScale); 
                        aimedScale += scaleDiff;
                        aimedScale = Mathf.Max(widget.MinScale, aimedScale);
                        aimedScale = Mathf.Min(widget.MaxScale, aimedScale);
                        previousScale = aimedScale;
                    },
                    child:new ClipRect
                    (
                        clipBehavior:Clip.hardEdge,
                        child:new Stack
                        (
                            children: new List<Widget>
                            {
                                new Positioned
                                (
                                    left: aimedOffset.dx,
                                    top: aimedOffset.dy,
                                    child: Transform.scale
                                    (
                                        scale: aimedScale,
                                        child: new Container(
                                            key:ContentViewContainerKey,
                                            width: widget.ContentSizeWidth,
                                            height: widget.ContentSizeHeight,
                                            child:widget.child
                                        ),
                                        alignment:Alignment.topLeft
                                    )
                                )
                            }
                        )
                    )
                )
            );
        }
    }
}

using System;
using Unity.UIWidgets.foundation;
using Unity.UIWidgets.material;
using Unity.UIWidgets.ui;
using Unity.UIWidgets.widgets;
using UnityEngine;
using Canvas = Unity.UIWidgets.ui.Canvas;
using Color = Unity.UIWidgets.ui.Color;

namespace FinGameWorks.Scripts.Views
{
    public class GridPointViewPainter : AbstractCustomPainter
    {
        private readonly float radius = 2f;
        private readonly float spacing = 60.0f;
        private Color color = Color.white;

        public GridPointViewPainter(float radius = 2, float spacing = 60.0f, Color color = null, Listenable repaint = null) : base(repaint)
        {
            this.radius = radius;
            this.spacing = spacing;
            this.color = color == null ? Colors.white : color;
        }

        public override void paint(Canvas canvas, Size size)
        {
            Path path = new Path();
            for (int x = 1; x < size.width / spacing; x++)
            {
                for (int y = 1; y < size.height / spacing; y++)
                {
                    path.addCircle(x * spacing,y * spacing, radius);
                }
            }

            Paint paint = new Paint
            {
                strokeWidth = 0,
                color = color,
                strokeCap = StrokeCap.round,
                strokeJoin = StrokeJoin.round,
                style = PaintingStyle.fill
            };
            canvas.drawPath(path,paint);
            
        }

        public override bool shouldRepaint(CustomPainter oldDelegate)
        {
            return true;
        }
    }

    public class GridPointView : StatefulWidget
    {
        public Widget Child;
        public readonly float Radius;
        public readonly float Spacing;
        public readonly float Opacity;
        
        public GridPointView(float radius = 2, float spacing = 60.0f, float opacity = 0.1f, Widget child = null, Key key = null) : base(key)
        {
            Child = child;
            Radius = radius;
            Spacing = spacing;
            Opacity = opacity;
        }

        public override State createState()
        {
            return new GridPointViewState();
        }
    }

    public class GridPointViewState : State<GridPointView>
    {
        public override Widget build(BuildContext context)
        {
            return new CustomPaint
            (
                painter: new GridPointViewPainter
                (
                    widget.Radius,
                    widget.Spacing,
                    Theme.of(context).dividerColor.withOpacity(widget.Opacity)
                ),
                isComplex: true,
                willChange: true,
                child: widget.Child
            );
        }
    }
}

using System.Collections.Generic;
using Unity.UIWidgets.foundation;
using Unity.UIWidgets.material;
using Unity.UIWidgets.widgets;
using UnityEngine;

namespace FinGameWorks.Scripts.Views
{
    public class AppMainScreen : StatefulWidget
    {
        public override State createState()
        {
            return new AppMainScreenState();
        }
    }

    class AppMainScreenState : State<AppMainScreen>
    {
        public override Widget build(BuildContext context)
        {
            return new Scaffold
            (
                body: new SafeArea
                (
                    child: new ScrollView(child: new GridPointView(1.5f,
                                35,
                                0.2f))
                )
            );
        }
    }
}

(Or we can transfer the whole project on WeChat)

Usage

Notice the output of Debug.Log("scaleDiff = " + scaleDiff);

Environment:

• Unity 2018.3.11f1
• UIWidgets commit d76d75340e015215c58b2fa12c39f68ff1df25d9
• Auto Graphics API

Issue: When exported to WebGL, my project using UIWidgets won't display the UI on Chrome (showing default Skybox), but it works well on Safari (see images below). You can visit https://wizardly-goodall-109263.netlify.com/ for a test. The console in Chrome didn't throw any error when loading the scene. 🤔

Attachment: https://www.dropbox.com/s/2ajywuu8ybbxxol/UIWidgets-Chrome-Issue-Sample.zip?dl=0

按照指南在现有游戏项目中加入示例时，游戏运行会变得非常卡顿。所以我不得不用以下代码来避免游戏卡顿： Window.onFrameRateSpeedUp = () => { }; Window.onFrameRateCoolDown = () => { }; 但是我不知道这样会不会产生其他影响，所以想问一下这是在游戏项目中使用UIWidgets必须设置的步骤吗？还是我有什么地方没有注意到而导致了这种卡顿？

When I use the stack widget like in flutter, I can't dynamically modify the children property to change the z-order of the child widgets.

The following code can achieve the effect in flutter, but it has no effect in UIWidgets.

我像 flutter 中那样使用 Stack widget 时，发现我不能动态修改children属性来改变子widget的前后顺序。

以下代码可以在flutter中实现效果，但在UIWidgets中没有效果。

flutter

class MyHomePage extends StatefulWidget {
  final String title;
  MyHomePage({Key? key, required this.title}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  var children = <Widget>[
    Positioned(
        top: 100,
        left: 100,
        child: Container(height: 100, width: 100, color: Colors.blue)),
    Positioned(
        top: 120,
        left: 120,
        child: Container(height: 100, width: 100, color: Colors.red))
  ];

  void _incrementCounter() {
    setState(() {
      var temp = children[0];
      children[0] = children[1];
      children[1] = temp;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(child: Stack(children: children)),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

C#

class MainUI : StatefulWidget
{
    public MainUI(Key key = null) : base(key) { }

    public override State createState()
    {
        return new MainUIState();
    }
}

class MainUIState: State<MainUI>
{
    int counter = 0;

    public override Widget build(BuildContext context)
    {
        List<Widget> widgets = new List<Widget>()
        {
            new Positioned(
            top: 100,
            left: 100,
            child: new Container(height : 100, width : 100, color : Colors.blue)),
            new Positioned(
            top: 120,
            left: 120,
            child: new Container(height : 100, width : 100, color : Colors.red))
        };

        return new ConstrainedBox(
            constraints: BoxConstraints.expand(),
            child: new Stack(
                children : new List<Widget>()
                {
                    new Column(
                            children: new List<Widget>()
                            {
                                new Expanded(
                                        child: new Row(
                                            crossAxisAlignment : CrossAxisAlignment.start,
                                            children : new List<Widget>()
                                            {
                                                new RaisedButton(
                                                    onPressed: () =>
                                                    {
                                                        this.setState(() =>
                                                        {
                                                            Widget temp = widgets[0];
                                                            widgets[0] = widgets[1];
                                                            widgets[1] = temp;
                                                        });
                                                    },
                                                    child : new Text("交换")
                                                )
                                            }
                                        )
                                    )
                            }
                        ),
                        new Stack(
                            children: widgets
                        )
                }
            )
        );
    }
}

在文本输入框中，若想使用文本居中对齐或者右对齐的时候，文本内容会和光标之间有偏移。

复现问题： 1、创建一个文本输入框； 2、更改属性textAlign为非left； 3、输入字符内容；（这时候光标不会处于文本最后方） 4、长按输入文本框、全选。（这时候会发现显示的文本内容，和选中阴影不一致，严重偏移）

希望大佬们尽快解决该问题，拜谢。！

本人2020.2.1f1版本：

1. Edit ->Project Settings -> Package Manager -> Advanced Settings -> Enable Preview Packages 打勾（非必要，只是顺带介绍一下新版本包管理器的预览版开关）
2. Window -> Package Manager， 点击左上角+号，选择第三个add package from git URL，输入com.unity.uiwidgets即可导入