Map for WPF - How to Implement a Custom Map Data Provider

C#
using System;
using System.Globalization;
using System.Net;
using System.Windows;
using DevExpress.Xpf.Map;

namespace CustomMapDataProviderApp {

    public partial class MainWindow : Window {
        public MainWindow () {
            InitializeComponent();
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
            CustomMapDataProvider provider = new CustomMapDataProvider();
            imageLayer.DataProvider = provider;
            provider.WebRequest += Provider_WebRequest;
        }

        private void Provider_WebRequest(object sender, MapWebRequestEventArgs e) {
            e.UserAgent = "Test Map App";
        }
    }

    public class CustomMapDataProvider : MapDataProviderBase {
        readonly SphericalMercatorProjection projection = new SphericalMercatorProjection();

        public override ProjectionBase Projection { get { return projection; } }

        public CustomMapDataProvider () {
            SetTileSource(new CustomTileSource());
        }
        protected override MapDependencyObject CreateObject () {
            return new CustomMapDataProvider();
        }
        public override Size GetMapSizeInPixels (double zoomLevel) {
            return new Size(Math.Pow(2.0, zoomLevel) * OpenStreetMapTileSource.tileSize, 
                Math.Pow(2.0, zoomLevel) * OpenStreetMapTileSource.tileSize);
        }
    }

    public class CustomTileSource : MapTileSourceBase {
        const string roadUrlTemplate = 
            @"http://{subdomain}.tile.openstreetmap.org/{tileLevel}/{tileX}/{tileY}.png";
        public const int maxZoomLevel = 20;
        public const int tileSize = 256;

        static int imageWidth = (int)Math.Pow(2.0, maxZoomLevel) * tileSize;
        static int imageHeight = (int)Math.Pow(2.0, maxZoomLevel) * tileSize;
        static string[] subdomains = new string[] { "a", "b", "c" };

        public CustomTileSource ()
            : base(imageWidth, imageHeight, tileSize, tileSize) {

        }
        public override Uri GetTileByZoomLevel (int zoomLevel, long tilePositionX, long tilePositionY) {
            string url = roadUrlTemplate;
            url = url.Replace("{tileX}", tilePositionX.ToString(CultureInfo.InvariantCulture));
            url = url.Replace("{tileY}", tilePositionY.ToString(CultureInfo.InvariantCulture));
            url = url.Replace("{tileLevel}", zoomLevel.ToString(CultureInfo.InvariantCulture));
            url = url.Replace("{subdomain}", subdomains[GetSubdomainIndex(subdomains.Length)]);
            return new Uri(url);
        }
    }
}

Visual Basic
Imports System
Imports System.Globalization
Imports System.Net
Imports System.Windows
Imports DevExpress.Xpf.Map

Namespace CustomMapDataProviderApp

    Public Partial Class MainWindow
        Inherits Window

        Public Sub New()
            Me.InitializeComponent()
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
            Dim provider As CustomMapDataProvider = New CustomMapDataProvider()
            Me.imageLayer.DataProvider = provider
            AddHandler provider.WebRequest, AddressOf Provider_WebRequest
        End Sub

        Private Sub Provider_WebRequest(ByVal sender As Object, ByVal e As MapWebRequestEventArgs)
            e.UserAgent = "Test Map App"
        End Sub
    End Class

    Public Class CustomMapDataProvider
        Inherits MapDataProviderBase

        Private ReadOnly projectionField As SphericalMercatorProjection = New SphericalMercatorProjection()

        Public Overrides ReadOnly Property Projection As ProjectionBase
            Get
                Return projectionField
            End Get
        End Property

        Public Sub New()
            SetTileSource(New CustomTileSource())
        End Sub

        Protected Overrides Function CreateObject() As MapDependencyObject
            Return New CustomMapDataProvider()
        End Function

        Public Overrides Function GetMapSizeInPixels(ByVal zoomLevel As Double) As Size
            Return New Size(Math.Pow(2.0, zoomLevel) * OpenStreetMapTileSource.tileSize, Math.Pow(2.0, zoomLevel) * OpenStreetMapTileSource.tileSize)
        End Function
    End Class

    Public Class CustomTileSource
        Inherits MapTileSourceBase

        Const roadUrlTemplate As String = "http://{subdomain}.tile.openstreetmap.org/{tileLevel}/{tileX}/{tileY}.png"

        Public Const maxZoomLevel As Integer = 20

        Public Const tileSize As Integer = 256

        Private Shared imageWidth As Integer = CInt(Math.Pow(2.0, maxZoomLevel)) * tileSize

        Private Shared imageHeight As Integer = CInt(Math.Pow(2.0, maxZoomLevel)) * tileSize

        Private Shared subdomains As String() = New String() {"a", "b", "c"}

        Public Sub New()
            MyBase.New(imageWidth, imageHeight, tileSize, tileSize)
        End Sub

        Public Overrides Function GetTileByZoomLevel(ByVal zoomLevel As Integer, ByVal tilePositionX As Long, ByVal tilePositionY As Long) As Uri
            Dim url As String = roadUrlTemplate
            url = url.Replace("{tileX}", tilePositionX.ToString(CultureInfo.InvariantCulture))
            url = url.Replace("{tileY}", tilePositionY.ToString(CultureInfo.InvariantCulture))
            url = url.Replace("{tileLevel}", zoomLevel.ToString(CultureInfo.InvariantCulture))
            url = url.Replace("{subdomain}", subdomains(GetSubdomainIndex(subdomains.Length)))
            Return New Uri(url)
        End Function
    End Class
End Namespace