将SkiaSharp的PaintSurface与Xamarin形式和棱镜绑定

Question

I'm trying to get SkiaSharp working with Xamarin Forms and Prism. I have it working with the following page behind code

public partial class RoomLayoutPage : ContentPage 
{ 

SKCanvasView canvasView;

public RoomLayoutPage()
{
  InitializeComponent();

  canvasView = new SKCanvasView();
  canvasView.PaintSurface += OnCanvasViewPaintSurface;
  Content = canvasView;
}


private void OnCanvasViewPaintSurface(object sender, SKPaintSurfaceEventArgs e)
{
  SKSurface surface = e.Surface;
  SKCanvas canvas = surface.Canvas;

  canvas.Clear();

  SKPaint blackPaint = new SKPaint
  {
    Color = SKColors.Black,
  };

  canvas.DrawRect(0, 0, 100, 100, blackPaint);
}
}

but now I want to move this to my Prism ViewModel. If I move it then Content is not valid

1. How do I reference a xaml element from a ViewModel? I'd prefer not to do it this way because my ViewModel is then coupled to the view.

2. (Prefered way) If I put an SKCanvasView on my page

I can bind to the event with the EventToCommandBehaviour

    <forms:SKCanvasView>
  <forms:SKCanvasView.Behaviors>
    <behaviors:EventToCommandBehavior Command="{Binding OnCanvasViewPaintSurface}" EventName="PaintSurface"/>
  </forms:SKCanvasView.Behaviors>
</forms:SKCanvasView>

But I'm not sure how to bind the SKPaintSurfaceEventArgs for

OnCanvasViewPaintSurface = new DelegateCommand<SKPaintSurfaceEventArgs>(OnCanvasViewPaintAction);

I'm assuming it's one of the EventArgs options from here https://prismlibrary.github.io/docs/xamarin-forms/EventToCommandBehavior.html ?

Thank you

Answer 1

So using a value converter solves it..

public class SkiaEventArgsConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
  var sKPaintSurfaceEventArgs = value as SKPaintSurfaceEventArgs;
  if (sKPaintSurfaceEventArgs == null)
  {
    throw new ArgumentException("Expected value to be of type SKPaintSurfaceEventArgs", nameof(value));
  }

  return sKPaintSurfaceEventArgs;
}

public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
  throw new NotImplementedException();
}
}

Not entirely sure why it couldn't convert it automagically but it works