more pleasant progress handling, although somewhat flawed

frontend/lib/structs/landmark.dart

@@ -27,7 +27,7 @@ final class Landmark extends LinkedListEntry<Landmark>{
   String? imageURL; // not final because it can be patched
   final String? description;
   final Duration? duration;
-  final bool? visited;
+  bool visited;
 
   // Next node
   // final Landmark? next;
@@ -46,7 +46,7 @@ final class Landmark extends LinkedListEntry<Landmark>{
     this.imageURL,
     this.description,
     this.duration,
-    this.visited,
+    this.visited = false,
 
     // this.next,
     this.tripTime,
@@ -71,7 +71,7 @@ final class Landmark extends LinkedListEntry<Landmark>{
       final imageURL = json['image_url'] as String?;
       final description = json['description'] as String?;
       var duration = Duration(minutes: json['duration'] ?? 0) as Duration?;
-      final visited = json['visited'] as bool?;
+      final visited = json['visited'] ?? false as bool;
       var tripTime = Duration(minutes: json['time_to_reach_next'] ?? 0) as Duration?;
       
       return Landmark(

frontend/lib/structs/trip.dart

@@ -52,6 +52,7 @@ class Trip with ChangeNotifier {
     totalTime = json['total_time'];
     notifyListeners();
   }
+
   void addLandmark(Landmark landmark) {
     landmarks.add(landmark);
     notifyListeners();
@@ -66,12 +67,16 @@ class Trip with ChangeNotifier {
     landmarks.remove(landmark);
     notifyListeners();
   }
-  
+
   void updateError(String error) {
     errorDescription = error;
     notifyListeners();
   }
 
+  void notifyUpdate(){
+    notifyListeners();
+  }
+
   factory Trip.fromPrefs(SharedPreferences prefs, String uuid) {
     String? content = prefs.getString('trip_$uuid');
     Map<String, dynamic> json = jsonDecode(content!);
@@ -80,7 +85,6 @@ class Trip with ChangeNotifier {
     log('Loading trip $uuid with first landmark $firstUUID');
     LinkedList<Landmark> landmarks = readLandmarks(prefs, firstUUID);
     trip.landmarks = landmarks;
-    // notifyListeners();
     return trip;
   }