more pleasant progress handling, although somewhat flawed

frontend/lib/modules/current_trip_map.dart

@@ -9,14 +9,10 @@ import 'package:google_maps_flutter/google_maps_flutter.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:widget_to_marker/widget_to_marker.dart';
 
-
 class CurrentTripMap extends StatefulWidget {
-
   final Trip? trip;
 
-  CurrentTripMap({
-    this.trip
-  });
+  CurrentTripMap({this.trip});
 
   @override
   State<CurrentTripMap> createState() => _CurrentTripMapState();
@@ -30,7 +26,23 @@ class _CurrentTripMapState extends State<CurrentTripMap> {
     zoom: 11.0,
   );
   Set<Marker> mapMarkers = <Marker>{};
-  
+  Set<Polyline> mapPolylines = <Polyline>{};
+
+  @override
+  void initState() {
+    super.initState();
+    widget.trip?.addListener(setMapMarkers);
+    widget.trip?.addListener(setMapRoute);
+
+  }
+
+  @override
+  void dispose() {
+    widget.trip?.removeListener(setMapMarkers);
+    widget.trip?.removeListener(setMapRoute);
+    
+    super.dispose();
+  }
 
   void _onMapCreated(GoogleMapController controller) async {
     mapController = controller;
@@ -40,16 +52,17 @@ class _CurrentTripMapState extends State<CurrentTripMap> {
       controller.moveCamera(update);
     }
     setMapMarkers();
+    setMapRoute();
   }
 
   void _onCameraIdle() {
     // print(mapController.getLatLng(ScreenCoordinate(x: 0, y: 0)));
   }
 
-
   void setMapMarkers() async {
     List<Landmark> landmarks = widget.trip?.landmarks.toList() ?? [];
-    Set<Marker> newMarkers = <Marker>{};
+    Set<Marker> markers = <Marker>{};
+
     for (int i = 0; i < landmarks.length; i++) {
       Landmark landmark = landmarks[i];
       List<double> location = landmark.location;
@@ -58,20 +71,47 @@ class _CurrentTripMapState extends State<CurrentTripMap> {
         position: LatLng(location[0], location[1]),
         icon: await ThemedMarker(landmark: landmark, position: i).toBitmapDescriptor(
           logicalSize: const Size(150, 150),
-          imageSize: const Size(150, 150)
+          imageSize: const Size(150, 150),
         ),
       );
-      newMarkers.add(marker);
+      markers.add(marker);
     }
     setState(() {
-      mapMarkers = newMarkers;
+      mapMarkers = markers;
     });
   }
 
+  void setMapRoute() async {
+    List<Landmark> landmarks = widget.trip?.landmarks.toList() ?? [];
+    Set<Polyline> polyLines = <Polyline>{};
+
+    if (landmarks.length < 2) {
+      return;
+    }
+
+    for (Landmark landmark in landmarks) {
+      if (landmark.next != null) {
+        List<LatLng> step = [
+          LatLng(landmark.location[0], landmark.location[1]),
+          LatLng(landmark.next!.location[0], landmark.next!.location[1])
+        ];
+        Polyline stepLine = Polyline(
+          polylineId: PolylineId('step-${landmark.uuid}'),
+          points: step,
+          color: landmark.visited ? Colors.grey : PRIMARY_COLOR,
+          width: 5,
+        );
+        polyLines.add(stepLine);
+      }
+    }
+
+    setState(() {
+      mapPolylines = polyLines;
+    });
+  }
 
   @override
   Widget build(BuildContext context) {
-    widget.trip?.addListener(setMapMarkers);
     Future<SharedPreferences> preferences = SharedPreferences.getInstance();
 
     return FutureBuilder(
@@ -84,7 +124,7 @@ class _CurrentTripMapState extends State<CurrentTripMap> {
         } else {
           return const CircularProgressIndicator();
         }
-      }
+      },
     );
   }
 
@@ -93,8 +133,8 @@ class _CurrentTripMapState extends State<CurrentTripMap> {
       onMapCreated: _onMapCreated,
       initialCameraPosition: _cameraPosition,
       onCameraIdle: _onCameraIdle,
-      // onLongPress: ,
       markers: mapMarkers,
+      polylines: mapPolylines,
       cloudMapId: MAP_ID,
       mapToolbarEnabled: false,
       zoomControlsEnabled: false,
@@ -102,5 +142,4 @@ class _CurrentTripMapState extends State<CurrentTripMap> {
       myLocationButtonEnabled: false,
     );
   }
-
 }