TileSource/TileImageLoader

MBTiles/Shared/MBTileSource.cs

@@ -24,8 +24,6 @@ namespace MapControl.MBTiles
 
         public IDictionary<string, string> Metadata { get; } = new Dictionary<string, string>();
 
-        public override bool Cacheable => false;
-
         public async Task OpenAsync(string file)
         {
             Close();
@@ -34,14 +32,13 @@ namespace MapControl.MBTiles
 
             await connection.OpenAsync();
 
-            using (var command = new SQLiteCommand("select * from metadata", connection))
+            using var command = new SQLiteCommand("select * from metadata", connection);
-            {
-                var reader = await command.ExecuteReaderAsync();
 
-                while (await reader.ReadAsync())
+            var reader = await command.ExecuteReaderAsync();
-                {
+
-                    Metadata[(string)reader["name"]] = (string)reader["value"];
+            while (await reader.ReadAsync())
-                }
+            {
+                Metadata[(string)reader["name"]] = (string)reader["value"];
             }
         }
 
@@ -66,18 +63,17 @@ namespace MapControl.MBTiles
 
             try
             {
-                using (var command = new SQLiteCommand("select tile_data from tiles where zoom_level=@z and tile_column=@x and tile_row=@y", connection))
+                using var command = new SQLiteCommand("select tile_data from tiles where zoom_level=@z and tile_column=@x and tile_row=@y", connection);
+
+                command.Parameters.AddWithValue("@z", zoomLevel);
+                command.Parameters.AddWithValue("@x", x);
+                command.Parameters.AddWithValue("@y", (1 << zoomLevel) - y - 1);
+
+                var buffer = (byte[])await command.ExecuteScalarAsync();
+
+                if (buffer?.Length > 0)
                 {
-                    command.Parameters.AddWithValue("@z", zoomLevel);
+                    image = await ImageLoader.LoadImageAsync(buffer);
-                    command.Parameters.AddWithValue("@x", x);
-                    command.Parameters.AddWithValue("@y", (1 << zoomLevel) - y - 1);
-
-                    var buffer = (byte[])await command.ExecuteScalarAsync();
-
-                    if (buffer?.Length > 0)
-                    {
-                        image = await LoadImageAsync(buffer);
-                    }
                 }
             }
             catch (Exception ex)
@@ -87,10 +83,5 @@ namespace MapControl.MBTiles
 
             return image;
         }
-
-        public override Uri GetUri(int zoomLevel, int column, int row)
-        {
-            throw new NotSupportedException();
-        }
     }
 }

MapControl/Shared/TileImageLoader.cs

@@ -13,13 +13,13 @@ namespace MapControl
     public interface ITileImageLoader
     {
         /// <summary>
-        /// Loads all pending tiles from the tiles collection.
+        /// Loads all pending tiles from the tiles collection. Tile image caching is enabled
-        /// Tile image caching is enabled when tileSource.UriFormat starts with "http" and cacheName is a non-empty string.
+        /// when cacheName is a non-empty string and tiles are loaded from http or https Uris.
         /// </summary>
         void BeginLoadTiles(IEnumerable<Tile> tiles, TileSource tileSource, string cacheName, IProgress<double> progress);
 
         /// <summary>
-        /// Cancels a potentially ongoing tile loading task.
+        /// Terminates all running tile loading tasks.
         /// </summary>
         void CancelLoadTiles();
     }
@@ -76,7 +76,7 @@ namespace MapControl
 
         public void BeginLoadTiles(IEnumerable<Tile> tiles, TileSource tileSource, string cacheName, IProgress<double> progress)
         {
-            if (Cache == null || !tileSource.Cacheable)
+            if (Cache == null)
             {
                 cacheName = null; // disable caching
             }
@@ -142,25 +142,26 @@ namespace MapControl
 
                 try
                 {
-                    // Pass tileSource.LoadImageAsync calls to platform-specific method
+                    // Pass image loading callbacks to platform-specific method
                     // tile.LoadImageAsync(Func<Task<ImageSource>>) for completion in the UI thread.
 
-                    if (string.IsNullOrEmpty(cacheName))
+                    var uri = tileSource.GetUri(tile.ZoomLevel, tile.Column, tile.Row);
+
+                    if (uri == null)
                     {
                         await tile.LoadImageAsync(() => tileSource.LoadImageAsync(tile.ZoomLevel, tile.Column, tile.Row)).ConfigureAwait(false);
                     }
+                    else if (uri.Scheme != "http" && uri.Scheme != "https" || string.IsNullOrEmpty(cacheName))
+                    {
+                        await tile.LoadImageAsync(() => ImageLoader.LoadImageAsync(uri)).ConfigureAwait(false);
+                    }
                     else
                     {
-                        var uri = tileSource.GetUri(tile.ZoomLevel, tile.Column, tile.Row);
+                        var buffer = await LoadCachedBuffer(tile, uri, cacheName).ConfigureAwait(false);
 
-                        if (uri != null)
+                        if (buffer?.Length > 0)
                         {
-                            var buffer = await LoadCachedBuffer(tile, uri, cacheName).ConfigureAwait(false);
+                            await tile.LoadImageAsync(() => ImageLoader.LoadImageAsync(buffer)).ConfigureAwait(false);
-
-                            if (buffer?.Length > 0)
-                            {
-                                await tile.LoadImageAsync(() => tileSource.LoadImageAsync(buffer)).ConfigureAwait(false);
-                            }
                         }
                     }
                 }

MapControl/Shared/TileSource.cs

@@ -21,30 +21,18 @@ namespace MapControl
 #else
     [System.ComponentModel.TypeConverter(typeof(TileSourceConverter))]
 #endif
-    public abstract class TileSource
+    public class TileSource
     {
         /// <summary>
-        /// Indicates whether tile images from this source should be cached.
+        /// Gets the image request Uri for the specified zoom level and tile indices.
+        /// May return null when the image shall be loaded by the LoadImageAsync method.
         /// </summary>
-        public abstract bool Cacheable { get; }
+        public virtual Uri GetUri(int zoomLevel, int column, int row) => null;
 
         /// <summary>
-        /// Gets the image Uri for the specified zoom level and tile indices.
+        /// Loads a tile image without an Uri.
         /// </summary>
-        public abstract Uri GetUri(int zoomLevel, int column, int row);
+        public virtual Task<ImageSource> LoadImageAsync(int zoomLevel, int column, int row) => null;
-
-        /// <summary>
-        /// Loads a tile image whithout caching.
-        /// </summary>
-        public abstract Task<ImageSource> LoadImageAsync(int zoomLevel, int column, int row);
-
-        /// <summary>
-        /// Loads a cacheable tile image from an encoded frame buffer.
-        /// </summary>
-        public virtual Task<ImageSource> LoadImageAsync(byte[] buffer)
-        {
-            return ImageLoader.LoadImageAsync(buffer);
-        }
 
         /// <summary>
         /// Creates a TileSource instance from an Uri template string.
@@ -78,8 +66,6 @@ namespace MapControl
 
         public string[] Subdomains { get; set; }
 
-        public override bool Cacheable => UriTemplate != null && UriTemplate.StartsWith("http");
-
         public override Uri GetUri(int zoomLevel, int column, int row)
         {
             Uri uri = null;
@@ -103,13 +89,6 @@ namespace MapControl
             return uri;
         }
 
-        public override Task<ImageSource> LoadImageAsync(int zoomLevel, int column, int row)
-        {
-            var uri = GetUri(zoomLevel, column, row);
-
-            return uri != null ? ImageLoader.LoadImageAsync(uri) : Task.FromResult((ImageSource)null);
-        }
-
         public override string ToString()
         {
             return UriTemplate;