improved performance and battery usage on older devices

lib/view/pages/files/files.dart

@@ -4,6 +4,8 @@ import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:persistent_bottom_nav_bar_v2/persistent_bottom_nav_bar_v2.dart';
 
+import '../../../api/marianumcloud/webdav/queries/list_files/cacheable_file.dart';
+import '../../../api/marianumcloud/webdav/queries/list_files/list_files_response.dart';
 import '../../../state/app/infrastructure/loadable_state/loadable_state.dart';
 import '../../../state/app/infrastructure/loadable_state/view/loadable_state_consumer.dart';
 import '../../../state/app/infrastructure/utility_widgets/bloc_module.dart';
@@ -47,6 +49,22 @@ class _FilesViewState extends State<_FilesView> {
   late bool currentSortDirection;
   late final StreamSubscription<String> _invalidationSub;
 
+  // The list builder also runs for loading flips and parent rebuilds; only a
+  // new listing or a changed sort needs another sort pass.
+  Object? _sortedKey;
+  List<CacheableFile> _sortedFiles = const [];
+
+  List<CacheableFile> _sorted(ListFilesResponse listing, bool foldersToTop) {
+    final key = (listing, currentSort, currentSortDirection, foldersToTop);
+    if (key == _sortedKey) return _sortedFiles;
+    _sortedKey = key;
+    return _sortedFiles = listing.sortBy(
+      sortOption: currentSort,
+      foldersToTop: foldersToTop,
+      reversed: currentSortDirection,
+    );
+  }
+
   // Cache key in FilesBloc's pathString format: '/' for root, otherwise
   // segments joined without leading/trailing slash.
   String get _myPathString => widget.path.isEmpty ? '/' : widget.path.join('/');
@@ -98,6 +116,11 @@ class _FilesViewState extends State<_FilesView> {
   @override
   Widget build(BuildContext context) {
     final bloc = context.read<FilesBloc>();
+    // Selected here, not in the LoadableStateConsumer child: that closure runs
+    // during the consumer's build, where this context may not subscribe.
+    final foldersToTop = context.select(
+      (SettingsCubit c) => c.state.fileSettings.sortFoldersToTop,
+    );
     return Scaffold(
       appBar: AppBar(
         title: Text(widget.path.isNotEmpty ? widget.path.last : 'Dateien'),
@@ -153,15 +176,7 @@ class _FilesViewState extends State<_FilesView> {
                     text: 'Der Ordner ist leer',
                   );
                 }
-                final files = listing.sortBy(
-                  sortOption: currentSort,
-                  foldersToTop: context
-                      .watch<SettingsCubit>()
-                      .val()
-                      .fileSettings
-                      .sortFoldersToTop,
-                  reversed: currentSortDirection,
-                );
+                final files = _sorted(listing, foldersToTop);
                 return ListView.builder(
                   padding: EdgeInsets.zero,
                   itemCount: files.length,