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Version 4.12.2 Improved TileImageLoader.Cache

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This commit is contained in:
ClemensF 2019-07-18 21:09:54 +02:00
parent a25cc91c2f
commit 85287118a5
8 changed files with 139 additions and 116 deletions
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55
MapControl/WPF/TileImageLoader.WPF.cs
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@ -5,17 +5,21 @@
using System;
using System.IO;
using System.Runtime.Caching;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Media;
namespace MapControl
{
public class ImageCacheItem
{
public byte[] Buffer { get; set; }
public DateTime Expiration { get; set; }
}
public partial class TileImageLoader
{
/// <summary>
/// Default folder path where an ObjectCache instance may save cached data,
/// i.e. C:\ProgramData\MapControl\TileCache
/// Default folder path where an ObjectCache instance may save cached data, i.e. C:\ProgramData\MapControl\TileCache
/// </summary>
public static string DefaultCacheFolder
{
@ -23,17 +27,18 @@ namespace MapControl
}
/// <summary>
/// The ObjectCache used to cache tile images. The default is MemoryCache.Default.
/// An ObjectCache instance used to cache tile image data (i.e. ImageCacheItem objects).
/// The default ObjectCache value is MemoryCache.Default.
/// </summary>
public static ObjectCache Cache { get; set; } = MemoryCache.Default;
private static async Task LoadCachedTileImageAsync(Tile tile, Uri uri, string cacheKey)
{
DateTime expiration;
var buffer = GetCachedImage(cacheKey, out expiration);
var cacheItem = await GetCacheAsync(cacheKey).ConfigureAwait(false);
var buffer = cacheItem?.Buffer;
if (buffer == null || expiration < DateTime.UtcNow)
if (buffer == null || cacheItem.Expiration < DateTime.UtcNow)
{
var response = await ImageLoader.GetHttpResponseAsync(uri, false).ConfigureAwait(false);
@ -43,7 +48,7 @@ namespace MapControl
if (buffer != null) // tile image available
{
await SetCachedImage(cacheKey, buffer, GetExpiration(response.MaxAge)).ConfigureAwait(false);
await SetCacheAsync(cacheKey, buffer, GetExpiration(response.MaxAge)).ConfigureAwait(false);
}
}
}
@ -69,33 +74,25 @@ namespace MapControl
tile.Image.Dispatcher.InvokeAsync(() => tile.SetImage(image));
}
private static byte[] GetCachedImage(string cacheKey, out DateTime expiration)
private static Task<ImageCacheItem> GetCacheAsync(string cacheKey)
{
var buffer = Cache.Get(cacheKey) as byte[];
if (buffer != null && buffer.Length >= 16 &&
Encoding.ASCII.GetString(buffer, buffer.Length - 16, 8) == "EXPIRES:")
{
expiration = new DateTime(BitConverter.ToInt64(buffer, buffer.Length - 8), DateTimeKind.Utc);
}
else
{
expiration = DateTime.MinValue;
}
return buffer;
return Task.Run(() => Cache.Get(cacheKey) as ImageCacheItem);
}
private static async Task SetCachedImage(string cacheKey, byte[] buffer, DateTime expiration)
private static Task SetCacheAsync(string cacheKey, byte[] buffer, DateTime expiration)
{
using (var stream = new MemoryStream(buffer.Length + 16))
var imageCacheItem = new ImageCacheItem
{
await stream.WriteAsync(buffer, 0, buffer.Length).ConfigureAwait(false);
await stream.WriteAsync(Encoding.ASCII.GetBytes("EXPIRES:"), 0, 8).ConfigureAwait(false);
await stream.WriteAsync(BitConverter.GetBytes(expiration.Ticks), 0, 8).ConfigureAwait(false);
Buffer = buffer,
Expiration = expiration
};
Cache.Set(cacheKey, stream.ToArray(), new CacheItemPolicy { AbsoluteExpiration = expiration });
}
var cacheItemPolicy = new CacheItemPolicy
{
AbsoluteExpiration = expiration
};
return Task.Run(() => Cache.Set(cacheKey, imageCacheItem, cacheItemPolicy));
}
}
}