Refactor excursion_main.dart to implement a confirmation dialog on page exit, allowing users to save templates or exit without saving. Update TrackingService to support instance reset for better state management.

lib/screens/excursion/excursion_main.dart

@@ -458,8 +458,59 @@ class _ExcursionMainState extends State<ExcursionMain> {
           ),
         ];
 
-    // Begin of widget tree
-    return Scaffold(
+    return PopScope(
+      canPop: false,
+      onPopInvoked: (didPop) async {
+        if (didPop) {
+          return;
+        }
+        
+        // Show confirmation dialog
+        final result = await showDialog<int>(
+          context: context,
+          builder: (context) => AlertDialog(
+            title: const Text('Seite verlassen?'),
+            content: const Text('Möchten Sie die Seite wirklich verlassen?'),
+            actions: [
+              TextButton(
+                onPressed: () => Navigator.of(context).pop(0),
+                child: const Text('Nein'),
+              ),
+              TextButton(
+                onPressed: () => Navigator.of(context).pop(1),
+                child: const Text('Ja und Template speichern'),
+              ),
+              TextButton(
+                onPressed: () => Navigator.of(context).pop(2),
+                child: const Text('Ja ohne Template'),
+              ),
+            ],
+          ),
+        );
+
+        if (result == null || result == 0) {
+          return;
+        } else if (result == 1) {
+          // Save as template and leave
+          if (context.mounted) {
+            saveTemplate(
+              getFieldsText(),
+              DatabasesEnum.excursion,
+            );
+          }
+          TrackingService.resetInstance();
+          if (context.mounted) {
+            Navigator.of(context).pop();
+          }
+        } else {
+          // Just leave without saving
+          TrackingService.resetInstance();
+          if (context.mounted) {
+            Navigator.of(context).pop();
+          }
+        }
+      },
+      child: Scaffold(
         appBar: AppBar(
           title: Text(AppLocalizations.of(context)!.excursion),
           actions: [
@@ -550,6 +601,7 @@ class _ExcursionMainState extends State<ExcursionMain> {
             },
           ),
         ),
+      ),
     );
   }
 }

lib/services/tracking_service.dart

@@ -9,10 +9,22 @@ import 'package:latlong2/latlong.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
 class TrackingService {
-  static final TrackingService _instance = TrackingService._internal();
-  factory TrackingService() => _instance;
+  static TrackingService? _instance;
+  
+  factory TrackingService() {
+    _instance ??= TrackingService._internal();
+    return _instance!;
+  }
+  
   TrackingService._internal();
 
+  static void resetInstance() {
+    if (_instance != null) {
+      _instance!.dispose();
+      _instance = null;
+    }
+  }
+
   List<LatLng> pathList = [];
   List<double> accuracyList = [];
   Timer? _positionTimer;