Umstellung auf UTC Timestamp

lib/main.dart

@@ -3,6 +3,7 @@ import 'dart:async';
 import 'package:dart_mq/dart_mq.dart';
 import 'package:synchronized/synchronized.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:geolocator/geolocator.dart';
 import 'package:isar/isar.dart';
 import 'package:path_provider/path_provider.dart';
@@ -202,6 +203,7 @@ class Main extends StatefulWidget {
 }
 
 class _MainState extends State<Main> with SingleTickerProviderStateMixin, ProducerMixin, ConsumerMixin {
+  DateTime? _lastBackPressed;
   late ContentViewWidget _currentContent;
   late WidgetStack<ContentViewWidget> contentStack = WidgetStack();
 
@@ -274,12 +276,27 @@ class _MainState extends State<Main> with SingleTickerProviderStateMixin, Produc
     return ColoredSafeArea(
       key: GlobalKey(),
       child: PopScope(
-        canPop: contentStack.isNotEmpty,
+        canPop: false,
         onPopInvokedWithResult: (didPop, result) async {
           if (didPop) return;
 
           if (contentStack.isNotEmpty) {
             _popContentView(1);        // alten Inhalt entfernen
+          } else {
+            final now = DateTime.now();
+            if (_lastBackPressed == null || now.difference(_lastBackPressed!) > const Duration(seconds: 2)) {
+              _lastBackPressed = now;
+              if (mounted) {
+                ScaffoldMessenger.of(context).hideCurrentSnackBar();
+                ScaffoldMessenger.of(context).showSnackBar(
+                  const SnackBar(content: Text('Zum Beenden erneut Zurück drücken'), duration: Duration(seconds: 2)),
+                );
+              }
+            } else {
+              // Zweiter Zurück-Klick innerhalb des Zeitfensters: App beenden
+              // ignore: use_build_context_synchronously
+              SystemNavigator.pop();
+            }
           }
         },
         child: Scaffold(