Observe TileLayerOptions changes

lib/src/layer/tile_layer.dart

@@ -141,17 +141,30 @@ class TileLayerOptions extends LayerOptions {
   ///
   final Map<String, String> additionalOptions;
 
-  // Tiles will not update more than once every `updateInterval` milliseconds
-  // (default 200) when panning.
-  // It can be 0 (but it will calculating for loading tiles every frame when panning / zooming, flutter is fast)
-  // This can save some fps and even bandwidth
-  // (ie. when fast panning / animating between long distances in short time)
+  /// Tiles will not update more than once every `updateInterval`
+  /// (default 200 milliseconds) when panning.
+  /// It can be null (but it will calculating for loading tiles every frame when panning / zooming, flutter is fast)
+  /// This can save some fps and even bandwidth
+  /// (ie. when fast panning / animating between long distances in short time)
   final Duration updateInterval;
 
-  // Tiles fade in duration in milliseconds (default 100),
-  // it can 0 to avoid fade in
+  /// Tiles fade in duration in milliseconds (default 100),
+  /// it can be null to avoid fade in
   final Duration tileFadeInDuration;
 
+  /// Opacity start value when Tile starts fade in (0.0 - 1.0)
+  /// Takes effect if `tileFadeInDuration` is not null
+  final double tileFadeInStart;
+
+  /// Opacity start value when an exists Tile starts fade in with different Url (0.0 - 1.0)
+  /// Takes effect when `tileFadeInDuration` is not null and if `overrideTilesWhenUrlChanges` if true
+  final double tileFadeInStartWhenOverride;
+
+  /// `false`: current Tiles will be first dropped and then reload via new url (default)
+  /// `true`: current Tiles will be visible until new ones aren't loaded (new Tiles are loaded independently)
+  /// @see https://github.com/johnpryan/flutter_map/issues/583
+  final bool overrideTilesWhenUrlChanges;
+
   TileLayerOptions(
       {this.urlTemplate,
       this.tileSize = 256.0,
@@ -181,12 +194,18 @@ class TileLayerOptions extends LayerOptions {
       // Tiles fade in duration in milliseconds (default 100),
       // it can 0 to avoid fade in
       int tileFadeInDuration = 100,
+      this.tileFadeInStart = 0.0,
+      this.tileFadeInStartWhenOverride = 0.0,
+      this.overrideTilesWhenUrlChanges = false,
       rebuild})
       : updateInterval =
             updateInterval <= 0 ? null : Duration(milliseconds: updateInterval),
         tileFadeInDuration = tileFadeInDuration <= 0
             ? null
             : Duration(milliseconds: tileFadeInDuration),
+        assert(tileFadeInStart >= 0.0 && tileFadeInStart <= 1.0),
+        assert(tileFadeInStartWhenOverride >= 0.0 &&
+            tileFadeInStartWhenOverride <= 1.0),
         super(rebuild: rebuild);
 }
 
@@ -317,6 +336,49 @@ class _TileLayerState extends State<TileLayer> with TickerProviderStateMixin {
     _update(null);
     _moveSub = widget.stream.listen((_) => _handleMove());
 
+    _initThrottleUpdate();
+  }
+
+  @override
+  void didUpdateWidget(TileLayer oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    var reloadTiles = false;
+
+    if (oldWidget.options.tileSize != options.tileSize) {
+      _tileSize = CustomPoint(options.tileSize, options.tileSize);
+      reloadTiles = true;
+    }
+
+    if (oldWidget.options.updateInterval != options.updateInterval) {
+      _throttleUpdate?.close();
+      _initThrottleUpdate();
+    }
+
+    if (!reloadTiles) {
+      final oldUrl = oldWidget.options.wmsOptions?._encodedBaseUrl ??
+          oldWidget.options.urlTemplate;
+      final newUrl = options.wmsOptions?._encodedBaseUrl ?? options.urlTemplate;
+      if (oldUrl != newUrl) {
+        if (options.overrideTilesWhenUrlChanges) {
+          for (var tile in _tiles.values) {
+            tile.imageProvider = options.tileProvider
+                .getImage(_wrapCoords(tile.coords), options);
+            tile.loadTileImage();
+          }
+        } else {
+          reloadTiles = true;
+        }
+      }
+    }
+
+    if (reloadTiles) {
+      _removeAllTiles();
+      _resetView();
+      _update(null);
+    }
+  }
+
+  void _initThrottleUpdate() {
     if (options.updateInterval == null) {
       _throttleUpdate = null;
     } else {
@@ -331,12 +393,12 @@ class _TileLayerState extends State<TileLayer> with TickerProviderStateMixin {
 
   @override
   void dispose() {
-    super.dispose();
-
     _removeAllTiles();
     _moveSub?.cancel();
     options.tileProvider.dispose();
     _throttleUpdate?.close();
+
+    super.dispose();
   }
 
   @override
@@ -822,6 +884,8 @@ class _TileLayerState extends State<TileLayer> with TickerProviderStateMixin {
       print(error);
 
       tile.loadError = true;
+    } else {
+      tile.loadError = false;
     }
 
     var key = _tileCoordsToKey(coords);
@@ -830,12 +894,20 @@ class _TileLayerState extends State<TileLayer> with TickerProviderStateMixin {
       return;
     }
 
+    var fadeInStart = tile.loaded == null
+        ? options.tileFadeInStart
+        : options.tileFadeInStartWhenOverride;
     tile.loaded = DateTime.now();
     if (options.tileFadeInDuration == null ||
+        fadeInStart == 1.0 ||
         (tile.loadError && null == options.errorImage)) {
       tile.active = true;
     } else {
-      tile.startFadeInAnimation(options.tileFadeInDuration, this);
+      tile.startFadeInAnimation(
+        options.tileFadeInDuration,
+        this,
+        from: fadeInStart,
+      );
     }
 
     setState(() {});
@@ -896,7 +968,7 @@ class Tile implements Comparable<Tile> {
   final String coordsKey;
   final Coords<double> coords;
   final CustomPoint<num> tilePos;
-  final ImageProvider imageProvider;
+  ImageProvider imageProvider;
   final Level level;
 
   bool current;
@@ -929,10 +1001,20 @@ class Tile implements Comparable<Tile> {
     this.retain = false,
     this.loadError = false,
   }) {
+    loadTileImage();
+  }
+
+  void loadTileImage() {
     try {
+      final oldImageStream = _imageStream;
       _imageStream = imageProvider.resolve(ImageConfiguration());
-      _listener = ImageStreamListener(_tileOnLoad, onError: _tileOnError);
-      _imageStream.addListener(_listener);
+
+      if (_imageStream.key != oldImageStream?.key) {
+        oldImageStream?.removeListener(_listener);
+
+        _listener = ImageStreamListener(_tileOnLoad, onError: _tileOnError);
+        _imageStream.addListener(_listener);
+      }
     } catch (e, s) {
       // make sure all exception is handled - #444 / #536
       _tileOnError(e, s);
@@ -952,11 +1034,14 @@ class Tile implements Comparable<Tile> {
     _imageStream?.removeListener(_listener);
   }
 
-  void startFadeInAnimation(Duration duration, TickerProvider vsync) {
+  void startFadeInAnimation(Duration duration, TickerProvider vsync,
+      {double from}) {
+    animationController?.removeStatusListener(_onAnimateEnd);
+
     animationController = AnimationController(duration: duration, vsync: vsync)
       ..addStatusListener(_onAnimateEnd);
 
-    animationController.forward();
+    animationController.forward(from: from);
   }
 
   void _onAnimateEnd(AnimationStatus status) {
@@ -974,7 +1059,8 @@ class Tile implements Comparable<Tile> {
 
   void _tileOnError(dynamic exception, StackTrace stackTrace) {
     if (null != tileReady) {
-      tileReady(coords, exception, this);
+      tileReady(
+          coords, exception ?? 'Unknown exception during loadTileImage', this);
     }
   }