Added ImageTileSource.CanLoadAsync property. Changed Dispatcher.BeginInvoke calls in TileImageLoader.

MapControl/ImageTileSource.cs

@@ -0,0 +1,29 @@
+// WPF MapControl - http://wpfmapcontrol.codeplex.com/
+// Copyright © 2012 Clemens Fischer
+// Licensed under the Microsoft Public License (Ms-PL)
+
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+
+namespace MapControl
+{
+    /// <summary>
+    /// Provides the image of a map tile. ImageTileSource bypasses download and
+    /// cache processing in TileImageLoader. By overriding the LoadImage method,
+    /// an application can provide tile images from an arbitrary source.
+    /// If the CanLoadAsync property is true, the LoadImage method will be called
+    /// from a separate non-UI thread and must hence return a frozen ImageSource.
+    /// </summary>
+    public class ImageTileSource : TileSource
+    {
+        public virtual bool CanLoadAsync
+        {
+            get { return false; }
+        }
+
+        public virtual ImageSource LoadImage(int x, int y, int zoomLevel)
+        {
+            return new BitmapImage(GetUri(x, y, zoomLevel));
+        }
+    }
+}

MapControl/Location.cs

@@ -57,6 +57,9 @@ namespace MapControl
         }
     }
 
+    /// <summary>
+    /// Converts from string to Location.
+    /// </summary>
     public class LocationConverter : TypeConverter
     {
         public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)

MapControl/LocationCollection.cs

@@ -41,6 +41,9 @@ namespace MapControl
         }
     }
 
+    /// <summary>
+    /// Converts from string to LocationCollection.
+    /// </summary>
     public class LocationCollectionConverter : TypeConverter
     {
         public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)

MapControl/MapControl.csproj

@@ -46,6 +46,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="GlyphRunText.cs" />
+    <Compile Include="ImageTileSource.cs" />
     <Compile Include="Location.cs" />
     <Compile Include="LocationAnimation.cs" />
     <Compile Include="LocationCollection.cs" />

MapControl/TileImageLoader.cs

@@ -11,6 +11,7 @@ using System.Linq;
 using System.Net;
 using System.Runtime.Caching;
 using System.Threading;
+using System.Windows.Media;
 using System.Windows.Media.Imaging;
 using System.Windows.Threading;
 
@@ -84,18 +85,9 @@ namespace MapControl
         private void BeginGetTilesAsync(object newTilesList)
         {
             List<Tile> newTiles = (List<Tile>)newTilesList;
+            ImageTileSource imageTileSource = tileLayer.TileSource as ImageTileSource;
 
-            if (tileLayer.TileSource is ImageTileSource)
+            if (imageTileSource == null)
-            {
-                ImageTileSource imageTileSource = (ImageTileSource)tileLayer.TileSource;
-
-                foreach (Tile tile in newTiles)
-                {
-                    tileLayer.Dispatcher.BeginInvoke(DispatcherPriority.Background,
-                        (Action)(() => tile.SetSource(imageTileSource.GetImage(tile.XIndex, tile.Y, tile.ZoomLevel))));
-                }
-            }
-            else
             {
                 if (Cache == null)
                 {
@@ -143,6 +135,22 @@ namespace MapControl
                     ThreadPool.QueueUserWorkItem(DownloadTiles);
                 }
             }
+            else if (imageTileSource.CanLoadAsync)
+            {
+                foreach (Tile tile in newTiles)
+                {
+                    tileLayer.Dispatcher.BeginInvoke(DispatcherPriority.Background,
+                        (Action<Tile, ImageSource>)((t, s) => t.SetSource(s)), tile, imageTileSource.LoadImage(tile.XIndex, tile.Y, tile.ZoomLevel));
+                }
+            }
+            else
+            {
+                foreach (Tile tile in newTiles)
+                {
+                    tileLayer.Dispatcher.BeginInvoke(DispatcherPriority.Background,
+                        (Action<Tile>)(t => t.SetSource(imageTileSource.LoadImage(t.XIndex, t.Y, t.ZoomLevel))), tile);
+                }
+            }
         }
 
         private void DownloadTiles(object o)
@@ -188,7 +196,7 @@ namespace MapControl
                 return false;
             }
 
-            tileLayer.Dispatcher.BeginInvoke(DispatcherPriority.Background, (Action)(() => tile.SetSource(bitmap)));
+            tileLayer.Dispatcher.BeginInvoke(DispatcherPriority.Background, (Action<Tile>)(t => t.SetSource(bitmap)), tile);
             return true;
         }
 

MapControl/TileSource.cs

@@ -7,15 +7,13 @@ using System.ComponentModel;
 using System.Globalization;
 using System.Text;
 using System.Windows;
-using System.Windows.Media;
-using System.Windows.Media.Imaging;
 
 namespace MapControl
 {
     /// <summary>
     /// Provides the URI of a map tile.
     /// </summary>
-    [TypeConverter(typeof(TileSourceTypeConverter))]
+    [TypeConverter(typeof(TileSourceConverter))]
     public class TileSource
     {
         private Func<int, int, int, Uri> getUri;
@@ -156,23 +154,10 @@ namespace MapControl
         }
     }
 
-    /// <summary>
-    /// Provides the image of a map tile. ImageTileSource bypasses download and
-    /// cache processing in TileImageLoader. By overriding the GetImage method,
-    /// an application can provide tile images from an arbitrary source.
-    /// </summary>
-    public class ImageTileSource : TileSource
-    {
-        public virtual ImageSource GetImage(int x, int y, int zoomLevel)
-        {
-            return new BitmapImage(GetUri(x, y, zoomLevel));
-        }
-    }
-
     /// <summary>
     /// Converts from string to TileSource.
     /// </summary>
-    public class TileSourceTypeConverter : TypeConverter
+    public class TileSourceConverter : TypeConverter
     {
         public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
         {