improved performance and battery usage on older devices

lib/view/pages/foreign_timetable/element_picker_page.dart

@@ -7,6 +7,7 @@ import '../../../api/marianumconnect/queries/timetable_get_element_week/timetabl
 import '../../../api/marianumconnect/queries/timetable_get_rooms/timetable_get_rooms.dart';
 import '../../../api/marianumconnect/queries/timetable_get_students/timetable_get_students.dart';
 import '../../../api/marianumconnect/queries/timetable_get_teachers/timetable_get_teachers.dart';
+import '../../../model/account_data.dart';
 import '../../../state/app/modules/settings/bloc/settings_cubit.dart';
 import '../../../storage/timetable_favorites_settings.dart';
 import '../../../utils/haptics.dart';
@@ -31,7 +32,14 @@ class _ElementPickerPageState extends State<ElementPickerPage> {
 
   // One in-flight/resolved future per type so switching tabs (or rebuilds)
   // never re-fetches a list that's already loaded.
-  final Map<TimetableElementType, Future<List<_PickerItem>>> _futures = {};
+  // Session-wide (per account): the student list alone has 1000+ entries and
+  // used to be downloaded again every time the picker opened.
+  static final Map<
+    TimetableElementType,
+    ({int epoch, DateTime at, Future<List<_PickerItem>> items})
+  >
+  _futures = {};
+  static const Duration _listMaxAge = Duration(minutes: 15);
   // Memoised combined future for the "Alle" tab; rebuilt on retry.
   Future<List<_PickerItem>>? _allFuture;
 
@@ -47,8 +55,25 @@ class _ElementPickerPageState extends State<ElementPickerPage> {
     return _allFuture ??= _loadAll();
   }
 
-  Future<List<_PickerItem>> _loadFor(TimetableElementType type) =>
-      _futures.putIfAbsent(type, () => _fetch(type));
+  Future<List<_PickerItem>> _loadFor(TimetableElementType type) {
+    final epoch = AccountData().sessionEpoch;
+    final cached = _futures[type];
+    if (cached != null &&
+        cached.epoch == epoch &&
+        DateTime.now().difference(cached.at) < _listMaxAge) {
+      return cached.items;
+    }
+    final items = _fetch(type);
+    _futures[type] = (epoch: epoch, at: DateTime.now(), items: items);
+    // A failed load must not stick for the rest of the session.
+    items.then(
+      (_) {},
+      onError: (Object _) {
+        if (identical(_futures[type]?.items, items)) _futures.remove(type);
+      },
+    );
+    return items;
+  }
 
   Future<List<_PickerItem>> _loadAll() async {
     final lists = await Future.wait(TimetableElementType.values.map(_loadFor));
@@ -117,20 +142,16 @@ class _ElementPickerPageState extends State<ElementPickerPage> {
     Haptics.selection();
     // Hand the selection back to the timetable view, which renders the foreign
     // plan inline. We do not navigate to a new page.
-    Navigator.of(context).pop((
-      type: item.type,
-      id: item.id,
-      label: item.primary,
-    ));
+    Navigator.of(
+      context,
+    ).pop((type: item.type, id: item.id, label: item.primary));
   }
 
   void _openFavorite(FavoriteTimetableElement favorite) {
     Haptics.selection();
-    Navigator.of(context).pop((
-      type: favorite.type,
-      id: favorite.id,
-      label: favorite.label,
-    ));
+    Navigator.of(
+      context,
+    ).pop((type: favorite.type, id: favorite.id, label: favorite.label));
   }
 
   void _toggleFavorite(TimetableElementType type, int id, String label) {
@@ -325,9 +346,7 @@ class _ElementPickerPageState extends State<ElementPickerPage> {
     return ListTile(
       leading: Icon(_iconFor(item.type)),
       title: Text(item.primary),
-      subtitle: subtitleParts.isEmpty
-          ? null
-          : Text(subtitleParts.join(' · ')),
+      subtitle: subtitleParts.isEmpty ? null : Text(subtitleParts.join(' · ')),
       trailing: IconButton(
         icon: Icon(isFavorite ? Icons.star : Icons.star_border),
         tooltip: isFavorite ? 'Favorit entfernen' : 'Als Favorit markieren',