[Bug] TranslateTo not working repeatedly

[eli191]

Description

Move a view on user touch

Steps to Reproduce

1. Create a new Xamarin.Forms app with version 5.0.0.1874
2. Add Skiasharp.Views.Forms.2.80.2 package
3. Replace MainPage.xaml with below code

<?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:forms="clr-namespace:SkiaSharp.Views.Forms;assembly=SkiaSharp.Views.Forms"
    x:Class="TranslateTo.MainPage">

    <Grid
        x:Name="container"
        HorizontalOptions="FillAndExpand"
        VerticalOptions="FillAndExpand">
        <Frame
            x:Name="movingView"
            BackgroundColor="Blue"
            WidthRequest="50"
            HeightRequest="50"
            VerticalOptions="Start"
            HorizontalOptions="Start">
        </Frame>
        <forms:SKCanvasView
            HorizontalOptions="FillAndExpand"
            VerticalOptions="FillAndExpand"
            PaintSurface="OnPaintSurface"
            EnableTouchEvents="True"
            Touch="OnTouchAction" />
    </Grid>

</ContentPage>

4. Replace MainPage.xaml.cs with below code

public partial class MainPage : ContentPage
    {
        private void OnPaintSurface(object sender, SKPaintSurfaceEventArgs e)
        {
            SKImageInfo info = e.Info;
            viewportHeight = info.Height;
            viewportWidth = info.Width;
        }

        public async void OnTouchAction(object sender, SKTouchEventArgs e)
        {
            e.Handled = true;
            switch (e.ActionType)
            {
                case SKTouchAction.Pressed:
                    await movingView.ScaleTo(0.5, 0);
                    break;
                case SKTouchAction.Moved:
                    var location = e.Location;
                    var x = location.X * container.Width / viewportWidth;
                    var y = location.Y * container.Height / viewportHeight;
                    Console.WriteLine($"X={x}/{container.Width} Y={x}/{container.Height}");
                    await movingView.TranslateTo(x, y, 0);
                    break;
                case SKTouchAction.Released:
                    await movingView.TranslateTo(0, 0, 0);
                    await movingView.ScaleTo(1, 0);
                    break;
            }
        }

        private int viewportHeight;
        private int viewportWidth;

        public MainPage()
        {
            InitializeComponent();
        }
    }

Expected Behavior

View moves

Actual Behavior

View doesn't move (iOS)
App crashes (Android)

Basic Information

• Version with issue:
• Last known good version: ?
• Platform Target Frameworks:
  • iOS:
  • Android:
  • UWP:
• Android Support Library / AndroidX Version:
• NuGet Packages:
• Affected Devices:

Environment

Show/Hide Visual Studio info

Build Logs

Screenshots

Reproduction Link

https://github.com/eli191/translateto

Workaround

[themronion]

@eli191 I have a feeling there is a division by zero somewhere. Put a breakpoint before this line:

var x = location.X * container.Width / viewportWidth;

and see if viewportWidth is equal to 0

[hartez]

It's not a division by zero in this code, though something like that might be happening in the TranslateTo method in Forms.

@eli191 I tried changing the length parameter of TranslateTo from zero to 1 millisecond and that seems to prevent the crash. So if you need a workaround while we investigate this, you might give that a try.

[eli191]

Hi @hartez

You are a genius! effectively, putting 1 millisecond instead of 0 does the job very well!!
I am very happy with that workaround for now as it was blocking.

Thank you!