Added memory caching support to FlutterMapNetworkImageProvider

lib/src/layer/tile_layer/tile_layer.dart

@@ -24,22 +24,18 @@ part 'wms_tile_layer_options.dart';
 /// avoid issues.
 @immutable
 class TileLayer extends StatefulWidget {
- /// Defines the structure to create the URLs for the tiles. `{s}` means one of
- /// the available subdomains (can be omitted) `{z}` zoom level `{x}` and `{y}`
- /// — tile coordinates `{r}` can be used to add "@2x" to the URL to
- /// load retina tiles (can be omitted)
+ /// The URL template is a string that contains placeholders, which, when filled
+ /// in, create a URL/URI to a specific tile.
  ///
- /// Example:
- ///
- /// https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png
- ///
- /// Is translated to this:
- ///
- /// https://a.tile.openstreetmap.org/12/2177/1259.png
+ /// For more information, see <https://docs.fleaflet.dev/layers/tile-layer>.
  final String? urlTemplate;
 
- /// Follows the same structure as [urlTemplate]. If specified, this URL is
- /// used only if an error occurs when loading the [urlTemplate].
+ /// Fallback URL template, used if an error occurs when fetching tiles from
+ /// the [urlTemplate].
+ ///
+ /// Note that specifying this (non-null) will result in tiles not being cached
+ /// in memory. This is to avoid issues where the [urlTemplate] is flaky, to
+ /// prevent different tilesets being displayed at the same time.
  ///
  /// Avoid specifying this when using [AssetTileProvider] or [FileTileProvider],
  /// as these providers are less performant and efficient when this is

lib/src/layer/tile_layer/tile_provider/network_image_provider.dart

@@ -6,6 +6,10 @@ import 'package:flutter/painting.dart';
 import 'package:http/http.dart';
 
 /// Dedicated [ImageProvider] to fetch tiles from the network
+///
+/// Supports falling back to a secondary URL, if the primary URL fetch fails.
+/// Note that specifying a [fallbackUrl] will prevent this image provider from
+/// being cached.
 @immutable
 class FlutterMapNetworkImageProvider
  extends ImageProvider<FlutterMapNetworkImageProvider> {
@@ -14,15 +18,27 @@ class FlutterMapNetworkImageProvider
 
  /// The URL to fetch the tile from (GET request), in the event the original
  /// [url] request fails
+ ///
+ /// If this is non-null, [operator==] will always return `false` (except if
+ /// the two objects are [identical]). Therefore, if this is non-null, this
+ /// image provider will not be cached in memory.
  final String? fallbackUrl;
 
  /// The HTTP client to use to make network requests
+ ///
+ /// Not included in [operator==].
  final BaseClient httpClient;
 
  /// The headers to include with the tile fetch request
+ ///
+ /// Not included in [operator==].
  final Map<String, String> headers;
 
- /// Dedicated [ImageProvider] to fetch tiles from the network
+ /// Create a dedicated [ImageProvider] to fetch tiles from the network
+ ///
+ /// Supports falling back to a secondary URL, if the primary URL fetch fails.
+ /// Note that specifying a [fallbackUrl] will prevent this image provider from
+ /// being cached.
  const FlutterMapNetworkImageProvider({
  required this.url,
  required this.fallbackUrl,
@@ -75,4 +91,15 @@ class FlutterMapNetworkImageProvider
 
  return decode(await ImmutableBuffer.fromUint8List(bytes));
  }
+
+ @override
+ bool operator ==(Object other) =>
+ identical(this, other) ||
+ (other is FlutterMapNetworkImageProvider &&
+ fallbackUrl == null &&
+ url == other.url);
+
+ @override
+ int get hashCode =>
+ Object.hashAll([url, if (fallbackUrl != null) fallbackUrl]);
 }