fix timer state change

example/lib/main.dart

@@ -17,7 +17,7 @@ class _TrackTraceDemoState extends State<TrackTraceDemo> {
 
   @override
   void initState() {
-    Timer.periodic(const Duration(seconds: 10), (_) {
+    Timer.periodic(const Duration(seconds: 5), (_) {
       moveAlongRoute();
     });
     super.initState();
@@ -49,7 +49,7 @@ class _TrackTraceDemoState extends State<TrackTraceDemo> {
         line: const Polyline(
           polylineId: PolylineId('test route'),
           color: Colors.purple,
-          width: 7,
+          width: 5,
         ),
         onMapCreated: (ctr) => {
           controller = ctr,

lib/src/controller.dart

@@ -36,21 +36,39 @@ class TrackTraceController extends ChangeNotifier {
   }
 
   GoogleMapController? get mapController => _mapController;
+
+  @override
+  void dispose() {
+    _mapController?.dispose();
+    super.dispose();
+  }
 }
 
 class TrackTraceRoute {
   /// route duration in seconds
-  int duration = 0;
+  int _duration = 0;
 
   /// route distance in meters
-  int distance = 0;
+  int _distance = 0;
 
   /// route edge points
-  List<PointLatLng> line;
+  final List<PointLatLng> line;
 
   TrackTraceRoute(
       int durationValue, int distanceValue, List<PointLatLng> lineValue)
-      : duration = durationValue,
-        distance = distanceValue,
+      : _duration = durationValue,
+        _distance = distanceValue,
         line = lineValue;
+
+  int get distance => _distance;
+
+  int get duration => _duration;
+
+  set distance(int distance) {
+    _distance = distance;
+  }
+
+  set duration(int duration) {
+    _duration = duration;
+  }
 }

lib/src/google_map.dart

@@ -167,14 +167,16 @@ class _GoogleTrackTraceMapState extends State<GoogleTrackTraceMap> {
           (widget.timerPrecision == TimePrecision.everyMinute) ? 60 : 1;
       Timer.periodic(Duration(seconds: updateInterval), (timer) {
         if (controller.route != null) {
-          controller.route!.duration =
-              controller.route!.duration - updateInterval;
+          controller.route = TrackTraceRoute(
+              controller.route!.duration - updateInterval,
+              controller.route!.distance,
+              controller.route!.line);
         }
       });
     }
   }
 
-  void calculateRoute() async { 
+  void calculateRoute() async {
     DirectionsRepository() //TODO refactor this away
         .getDirections(
           origin: controller.start.position,