即使我遵循了教程代码，我的屏幕绘图的 Xamarin 代码也无法绘制

Question

大家好，我使用了本教程 (https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/graphics/skiasharp/paths/finger-paint) and modification with this forum post (https://forums.xamarin.com/discussion/178190/how-to-fix-cannot-convert-from-touchtracking-touchtrackingpoint-to-xamarin-forms-point) 中的代码来制作屏幕绘图。下面是我的 Xamarin C# 代码：

using System;
using System.Collections.Generic;
using SkiaSharp;
using SkiaSharp.Views.Forms;
using TouchTracking;
using Xamarin.Forms;

namespace MathKumu.Pages
{
    public partial class WorkPage : ContentPage
    {
        Dictionary<long, SKPath> inProgressPaths = new Dictionary<long, SKPath>();
        List<SKPath> completedPaths = new List<SKPath>();

        SKPaint paint = new SKPaint
        {
            Style = SKPaintStyle.Stroke,
            Color = SKColors.Black,
            StrokeWidth = 10,
            StrokeCap = SKStrokeCap.Round,
            StrokeJoin = SKStrokeJoin.Round
        };

        public WorkPage(TopicsData topic)
        {
            InitializeComponent();

            Title = topic.MathType;
        }

        void OnTouchEffectAction(object sender, TouchActionEventArgs args)
        {
            switch (args.Type)
            {
                case TouchActionType.Pressed:
                    if (!inProgressPaths.ContainsKey(args.Id))
                    {
                        SKPath path = new SKPath();
                        //path.MoveTo(ConvertToPixel(args.Location));
                        path.MoveTo(ConvertToPixel(new Point(args.Location.X, args.Location.Y)));
                        inProgressPaths.Add(args.Id, path);
                        canvasView.InvalidateSurface();
                    }
                    break;

                case TouchActionType.Moved:
                    if (inProgressPaths.ContainsKey(args.Id))
                    {
                        SKPath path = inProgressPaths[args.Id];
                        //path.LineTo(ConvertToPixel(args.Location));
                        path.MoveTo(ConvertToPixel(new Point(args.Location.X, args.Location.Y)));
                        canvasView.InvalidateSurface();
                    }
                    break;

                case TouchActionType.Released:
                    if (inProgressPaths.ContainsKey(args.Id))
                    {
                        completedPaths.Add(inProgressPaths[args.Id]);
                        inProgressPaths.Remove(args.Id);
                        canvasView.InvalidateSurface();
                    }
                    break;

                case TouchActionType.Cancelled:
                    if (inProgressPaths.ContainsKey(args.Id))
                    {
                        inProgressPaths.Remove(args.Id);
                        canvasView.InvalidateSurface();
                    }
                    break;
            }
        }

        //SKPoint ConvertToPixel(TouchTrackingPoint location)
        //{
        //    return new SKPoint((float)(canvasView.CanvasSize.Width * location.X / canvasView.Width),
        //                       (float)(canvasView.CanvasSize.Height * location.Y / canvasView.Height));
        //}

        SKPoint ConvertToPixel(Point pt)
        {
            return new SKPoint((float)(canvasView.CanvasSize.Width * pt.X / canvasView.Width),
                               (float)(canvasView.CanvasSize.Height * pt.Y / canvasView.Height));
        }

        void OnCanvasViewPaintSurface(object sender, SKPaintSurfaceEventArgs args)
        {
            SKCanvas canvas = args.Surface.Canvas;
            canvas.Clear();

            foreach (SKPath path in completedPaths)
            {
                canvas.DrawPath(path, paint);
            }

            foreach (SKPath path in inProgressPaths.Values)
            {
                canvas.DrawPath(path, paint);
            }
        }
    }
}

这是我的 xaml 代码：

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:skia="clr-namespace:SkiaSharp.Views.Forms;assembly=SkiaSharp.Views.Forms"
             xmlns:tt="clr-namespace:TouchTracking.Forms;assembly=TouchTracking.Forms"
             x:Class="MathKumu.Pages.WorkPage">
    <ContentPage.Content>
        <Grid BackgroundColor="White">
            <skia:SKCanvasView x:Name="canvasView"
                               PaintSurface="OnCanvasViewPaintSurface" />
            <Grid.Effects>
                <tt:TouchEffect Capture="True"
                                TouchAction="OnTouchEffectAction" />
            </Grid.Effects>
        </Grid>
    </ContentPage.Content>
</ContentPage>

在 iPhone 模拟器上它显示 canvas 但是无法绘制。你们能帮我解决这个问题吗？谢谢。

Answer 1

您可以尝试的一件事是使用内置触摸事件。

https://docs.microsoft.com/en-us/dotnet/api/skiasharp.views.forms.skcanvasview.touch?view=skiasharp-views-forms-1.68.1

我这里有一个示例可以做到这一点： https://github.com/mattleibow/SkiaSharpDemo/blob/master/SkiaSharpDemo/SkiaSharpDemo/MainPage.xaml.cs#L113

Answer 2

通过与@Jason 的对话，我不得不将 TouchEffect.cs 和 TouchRecognizer.cs 放入我项目的 .IOS 文件夹中。然后在我所有 xaml 文件所在的项目文件夹中，我必须放置 TouchActionEventArgs.cs、TouchActionEventHandler.cs、TouchActionType.cs 和 TouchEffect.cs。这全部来自 https://github.com/xamarin/xamarin-forms-samples/tree/master/Effects/TouchTrackingEffect/TouchTrackingEffect。毕竟我不得不清理项目，因为我之前有 NuGet 包 TouchTracking。谢谢@Jason 的帮助。

即使我遵循了教程代码，我的屏幕绘图的 Xamarin 代码也无法绘制

My Xamarin Code for on screen Drawing is not able to be Drawn on even though I followed tutorial code

c#

xaml

xamarin

xamarin.forms

skiasharp