XAML-Map-Control/MapControl/WinUI/MapImageLayer.WinUI.cs

using System;
#if UWP
using Windows.UI.Xaml.Media.Animation;
#else
using Microsoft.UI.Xaml.Media.Animation;
#endif

namespace MapControl;

public partial class MapImageLayer
{
    private void FadeOver()
    {
        var fadeInAnimation = new DoubleAnimation
        {
            To = 1d,
            Duration = MapBase.ImageFadeDuration
        };

        var fadeOutAnimation = new DoubleAnimation
        {
            To = 0d,
            BeginTime = MapBase.ImageFadeDuration,
            Duration = TimeSpan.Zero
        };

        Storyboard.SetTarget(fadeInAnimation, Children[1]);
        Storyboard.SetTargetProperty(fadeInAnimation, nameof(Opacity));

        Storyboard.SetTarget(fadeOutAnimation, Children[0]);
        Storyboard.SetTargetProperty(fadeOutAnimation, nameof(Opacity));

        var storyboard = new Storyboard();
        storyboard.Children.Add(fadeInAnimation);
        storyboard.Children.Add(fadeOutAnimation);
        storyboard.Begin();
    }
}