CrossFadeViewTransition.cs

using System.Threading;
using System.Threading.Tasks;
using Microsoft.Maui.Controls;
 
namespace NeuroAccessMaui.UI.Controls
{
    public sealed class CrossFadeViewTransition : IViewTransition
    {
        public async Task RunAsync(ViewSwitcherTransitionRequest request, CancellationToken cancellationToken)
        {
            if (request is null)
                return;
 
            if (!request.Animate)
                return;
 
            if (request.IsInitial)
                return;
 
            VisualElement? oldElement = request.OldView as VisualElement;
            VisualElement? newElement = request.NewView as VisualElement;
 
            if (oldElement is null && newElement is null)
                return;
 
            cancellationToken.ThrowIfCancellationRequested();
 
            Task? fadeOutTask = null;
            if (oldElement is not null)
            {
                fadeOutTask = oldElement.FadeToAsync(0.0, request.Duration / 2, request.Easing);
            }
 
            Task? fadeInTask = null;
            if (newElement is not null)
            {
                newElement.Opacity = 0.0;
                fadeInTask = newElement.FadeToAsync(1.0, request.Duration / 2, request.Easing);
            }
 
            if (fadeOutTask is not null && fadeInTask is not null)
            {
                await Task.WhenAll(fadeOutTask, fadeInTask).ConfigureAwait(false);
            }
            else if (fadeOutTask is not null)
            {
                await fadeOutTask.ConfigureAwait(false);
            }
            else if (fadeInTask is not null)
            {
                await fadeInTask.ConfigureAwait(false);
            }
        }
    }
}