Here's a quick and dirty implementation that should work:
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Layers;
namespace WpfApp5
{
public class OpenStreetMapLayer2 : TiledLayer, ICopyright
{
private const double WebMercatorCorner = 20037508.3427892;
private const string UserAgentName = "ArcGISRuntime-NET";
private const string UserAgentVersion = "10.2";
private static readonly string[] SubDomains = { "a", "b", "c" };
private static readonly TiledLayerInitializationInfo tileInfo;
private static readonly HttpClient client;
static OpenStreetMapLayer2()
{
var envelope = new Envelope(-WebMercatorCorner, -WebMercatorCorner, WebMercatorCorner, WebMercatorCorner, SpatialReferences.WebMercator);
double scale = 156543.03392804062;
double resolution = scale * 96.0 * 39.37;
Lod[] lods = new Lod[19];
for (int i = 0; i < lods.Length; i++)
{
lods[i] = new Lod(scale, resolution);
scale /= 2.0;
resolution /= 2.0;
}
tileInfo = new TiledLayerInitializationInfo(256, 256, -WebMercatorCorner, WebMercatorCorner, envelope, 96, lods);
client = new HttpClient(new WebRequestHandler()
{
AutomaticDecompression = System.Net.DecompressionMethods.GZip | System.Net.DecompressionMethods.Deflate,
CachePolicy = new System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.Default)
});
client.DefaultRequestHeaders.UserAgent.Add(new System.Net.Http.Headers.ProductInfoHeaderValue(UserAgentName, UserAgentVersion));
}
string ICopyright.CopyrightText => "Map data © OpenStreetMap contributors, CC-BY-SA";
protected override Task<TiledLayerInitializationInfo> OnInitializeTiledLayerRequestedAsync() => Task.FromResult(tileInfo);
protected override async Task<ImageTileData> GetTileDataAsync(int level, int row, int column, CancellationToken cancellationToken)
{
using (var response = await client.GetAsync(CreateUri(level, row, column), cancellationToken).ConfigureAwait(false))
{
using (var content = response.EnsureSuccessStatusCode().Content)
{
return new ImageTileData() { Column = column, Row = row, Level = level, ImageData = await content.ReadAsByteArrayAsync().ConfigureAwait(false) };
}
}
}
private static string CreateUri(int level, int row, int column)
{
string subdomain = SubDomains[(level + column + row) % SubDomains.Length];
return $"http://{subdomain}.tile.openstreetmap.org/{level}/{column}/{row}.png";
}
}
}
