XAML-Map-Control/MapControl/Tile.WPF.cs

// XAML Map Control - https://github.com/ClemensFischer/XAML-Map-Control
// © 2017 Clemens Fischer
// Licensed under the Microsoft Public License (Ms-PL)

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Media.Imaging;

namespace MapControl
{
    public partial class Tile
    {
        public void SetImage(ImageSource image, bool fadeIn = true)
        {
            Pending = false;

            if (Image.Dispatcher.CheckAccess())
            {
                SetImageSource(image, fadeIn);
            }
            else
            {
                Image.Dispatcher.BeginInvoke(new Action(() => SetImageSource(image, fadeIn)));
            }
        }

        private void SetImageSource(ImageSource image, bool fadeIn)
        {
            if (fadeIn && FadeDuration > TimeSpan.Zero)
            {
                var bitmap = image as BitmapSource;

                if (bitmap != null && !bitmap.IsFrozen && bitmap.IsDownloading)
                {
                    bitmap.DownloadCompleted += BitmapDownloadCompleted;
                    bitmap.DownloadFailed += BitmapDownloadFailed;
                }
                else
                {
                    Image.BeginAnimation(UIElement.OpacityProperty,
                        new DoubleAnimation(0d, 1d, FadeDuration));
                }
            }
            else
            {
                Image.Opacity = 1d;
            }

            Image.Source = image;
        }

        private void BitmapDownloadCompleted(object sender, EventArgs e)
        {
            var bitmap = (BitmapSource)sender;

            bitmap.DownloadCompleted -= BitmapDownloadCompleted;
            bitmap.DownloadFailed -= BitmapDownloadFailed;

            Image.BeginAnimation(UIElement.OpacityProperty,
                new DoubleAnimation(0d, 1d, FadeDuration));
        }

        private void BitmapDownloadFailed(object sender, ExceptionEventArgs e)
        {
            var bitmap = (BitmapSource)sender;

            bitmap.DownloadCompleted -= BitmapDownloadCompleted;
            bitmap.DownloadFailed -= BitmapDownloadFailed;

            Image.Source = null;
        }
    }
}