无法在Xamarin.iOS中为shimmer设置渐变层动画

using CoreAnimation;
using CoreGraphics;
using UIKit;

public class ShimmerView : UIView
{
    private CAGradientLayer gradientLayer;

    public ShimmerView(CGRect frame) : base(frame)
    {
        Initialize();
    }

    public ShimmerView(NSCoder coder) : base(coder)
    {
        Initialize();
    }

    private void Initialize()
    {
        gradientLayer = new CAGradientLayer();
        gradientLayer.Frame = Bounds;
        gradientLayer.Colors = new[] { UIColor.Clear.CGColor, UIColor.White.CGColor, UIColor.Clear.CGColor };
        gradientLayer.Locations = new NSNumber[] { 0.0, 0.5, 1.0 };
        gradientLayer.StartPoint = new CGPoint(0, 0.5);
        gradientLayer.EndPoint = new CGPoint(1, 0.5);
        Layer.Mask = gradientLayer;
    }

    public void StartShimmerAnimation()
    {
        var animation = new CABasicAnimation();
        animation.KeyPath = "locations";
        animation.Duration = 1.5;
        animation.RepeatCount = float.PositiveInfinity;
        animation.From = new NSNumber(-1.0);
        animation.To = new NSNumber(2.0);
        gradientLayer.AddAnimation(animation, "shimmerAnimation");
    }

    public void StopShimmerAnimation()
    {
        gradientLayer.RemoveAnimation("shimmerAnimation");
    }
}

public partial class ViewController : UIViewController
{
    private ShimmerView shimmerView;

    public override void ViewDidLoad()
    {
        base.ViewDidLoad();
        shimmerView = new ShimmerView(new CGRect(50, 50, 200, 50));
        View.AddSubview(shimmerView);
    }

    public override void ViewDidAppear(bool animated)
    {
        base.ViewDidAppear(animated);
        shimmerView.StartShimmerAnimation();
    }

    public override void ViewWillDisappear(bool animated)
    {
        base.ViewWillDisappear(animated);
        shimmerView.StopShimmerAnimation();
    }
}