XAML-Map-Control/MapControl/UWP/TileImageLoader.UWP.cs

// XAML Map Control - https://github.com/ClemensFischer/XAML-Map-Control
// © 2021 Clemens Fischer
// Licensed under the Microsoft Public License (Ms-PL)

using System;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading.Tasks;
using Windows.Storage;

namespace MapControl
{
    public partial class TileImageLoader
    {
        /// <summary>
        /// Default StorageFolder where an IImageCache instance may save cached data,
        /// i.e. ApplicationData.Current.TemporaryFolder.
        /// </summary>
        public static StorageFolder DefaultCacheFolder
        {
            get { return ApplicationData.Current.TemporaryFolder; }
        }

        /// <summary>
        /// The IImageCache implementation used to cache tile images. The default is null.
        /// </summary>
        public static Caching.IImageCache Cache { get; set; }


        private static async Task LoadCachedTileAsync(Tile tile, Uri uri, string cacheKey)
        {
            var cacheItem = await Cache.GetAsync(cacheKey).ConfigureAwait(false);
            var buffer = cacheItem?.Buffer;

            if (cacheItem == null || cacheItem.Expiration < DateTime.UtcNow)
            {
                var response = await ImageLoader.GetHttpResponseAsync(uri).ConfigureAwait(false);

                if (response != null) // download succeeded
                {
                    buffer = response.Buffer?.AsBuffer(); // may be null or empty when no tile available, but still be cached

                    await Cache.SetAsync(cacheKey, buffer, GetExpiration(response.MaxAge)).ConfigureAwait(false);
                }
            }

            if (buffer != null && buffer.Length > 0)
            {
                await tile.SetImageAsync(() => ImageLoader.LoadImageAsync(buffer)).ConfigureAwait(false);
            }
        }

        private static Task LoadTileAsync(Tile tile, TileSource tileSource)
        {
            return tile.SetImageAsync(() => tileSource.LoadImageAsync(tile.XIndex, tile.Y, tile.ZoomLevel));
        }
    }
}