implemented Nextcloud file previews for unknown file types using fileId and has-preview flags, updated file models, and refined manual refresh logic.

lib/api/marianumcloud/webdav/queries/list_files/cacheable_file.dart

@@ -15,6 +15,16 @@ class CacheableFile {
   DateTime? modifiedAt;
   String? sort;
 
+  /// Nextcloud's instance-local file id (`oc:fileid`). Used to address the
+  /// preview API by id, which is more reliable than the path-based variant
+  /// on some server configurations.
+  int? fileId;
+
+  /// Server's answer to "can I render a thumbnail for this file?"
+  /// (`nc:has-preview`). Lets the file viewer skip the placeholder text
+  /// when a preview is going to load anyway.
+  bool? hasPreview;
+
   CacheableFile({
     required this.path,
     required this.isDirectory,
@@ -24,6 +34,8 @@ class CacheableFile {
     this.eTag,
     this.createdAt,
     this.modifiedAt,
+    this.fileId,
+    this.hasPreview,
   });
 
   CacheableFile.fromDavFile(WebDavFile file) {
@@ -35,6 +47,8 @@ class CacheableFile {
     eTag = file.etag;
     createdAt = file.createdDate;
     modifiedAt = file.lastModified;
+    fileId = int.tryParse(file.fileId ?? '');
+    hasPreview = file.hasPreview;
   }
 
   factory CacheableFile.fromJson(Map<String, dynamic> json) =>

lib/api/marianumcloud/webdav/queries/list_files/cacheable_file.g.dart

@@ -20,6 +20,8 @@ CacheableFile _$CacheableFileFromJson(Map<String, dynamic> json) =>
       modifiedAt: json['modifiedAt'] == null
           ? null
           : DateTime.parse(json['modifiedAt'] as String),
+      fileId: (json['fileId'] as num?)?.toInt(),
+      hasPreview: json['hasPreview'] as bool?,
     )..sort = json['sort'] as String?;
 
 Map<String, dynamic> _$CacheableFileToJson(CacheableFile instance) =>
@@ -33,4 +35,6 @@ Map<String, dynamic> _$CacheableFileToJson(CacheableFile instance) =>
       'createdAt': instance.createdAt?.toIso8601String(),
       'modifiedAt': instance.modifiedAt?.toIso8601String(),
       'sort': instance.sort,
+      'fileId': instance.fileId,
+      'hasPreview': instance.hasPreview,
     };

lib/api/marianumcloud/webdav/queries/list_files/list_files.dart

@@ -25,8 +25,23 @@ class ListFiles extends WebdavApi<ListFilesParams> {
   Future<ListFilesResponse> run() async {
     final webdav = await WebdavApi.webdav;
     final timeout = _isRoot ? _rootTimeout : _subfolderTimeout;
+    // Explicit prop list — without it the server omits OC-namespaced
+    // properties like oc:fileid, which the preview endpoint relies on.
+    final prop = WebDavPropWithoutValues.fromBools(
+      davgetlastmodified: true,
+      davgetetag: true,
+      davgetcontenttype: true,
+      davgetcontentlength: true,
+      davresourcetype: true,
+      ocfileid: true,
+      ocsize: true,
+      nccreationtime: true,
+      nchaspreview: true,
+    );
     final davFiles =
-        (await webdav.propfind(PathUri.parse(params.path)).timeout(timeout))
+        (await webdav
+                .propfind(PathUri.parse(params.path), prop: prop)
+                .timeout(timeout))
             .toWebDavFiles();
     final files = davFiles.map(CacheableFile.fromDavFile).toSet();
 

lib/share_intent/remote_file_ref.dart

@@ -8,13 +8,33 @@ class RemoteFileRef {
   final String path;
   final String name;
 
-  const RemoteFileRef({required this.path, required this.name});
+  /// Nextcloud's instance-local file id, when known. Preferred over [path]
+  /// for hitting the preview API — the path-based variant is unreliable on
+  /// some server configurations.
+  final int? fileId;
+
+  /// Server's `nc:has-preview` flag when known. null = unknown.
+  final bool? hasPreview;
+
+  const RemoteFileRef({
+    required this.path,
+    required this.name,
+    this.fileId,
+    this.hasPreview,
+  });
 
   /// Caller must verify `file.path != null` first — Talk message parameters
   /// without a path (system events, mentions, polls) are not file refs.
-  factory RemoteFileRef.fromTalk(RichObjectString file) =>
+  factory RemoteFileRef.fromTalk(RichObjectString file) => RemoteFileRef(
-      RemoteFileRef(path: file.path!, name: file.name);
+    path: file.path!,
+    name: file.name,
+    fileId: int.tryParse(file.id),
+  );
 
-  factory RemoteFileRef.fromCacheable(CacheableFile file) =>
+  factory RemoteFileRef.fromCacheable(CacheableFile file) => RemoteFileRef(
-      RemoteFileRef(path: file.path, name: file.name);
+    path: file.path,
+    name: file.name,
+    fileId: file.fileId,
+    hasPreview: file.hasPreview,
+  );
 }

lib/state/app/modules/files/bloc/files_bloc.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:collection/collection.dart';
 
 import '../../../../../api/errors/error_mapper.dart';
@@ -42,6 +44,16 @@ class FilesBloc
     await _query(path, renew: true);
   }
 
+  /// LoadableState.reFetch (used by the pull-to-refresh indicator and the
+  /// error-screen retry button) routes through here. The inherited retry()
+  /// goes via gatherData() which respects the cache TTL — for an explicit
+  /// user-initiated reload we must bypass it, otherwise the root listing
+  /// silently returns its day-old cached payload without hitting the server.
+  @override
+  void retry() {
+    unawaited(refresh());
+  }
+
   Future<void> setPath(List<String> path) async {
     add(Emit((s) => s.copyWith(currentPath: path, listing: null)));
     add(RefetchStarted<FilesState>());

lib/widget/file_viewer.dart

@@ -3,6 +3,7 @@ import 'dart:convert';
 import 'dart:io';
 import 'dart:math';
 
+import 'package:cached_network_image/cached_network_image.dart';
 import 'package:chewie/chewie.dart';
 import 'package:file_picker/file_picker.dart';
 import 'package:flutter/material.dart';
@@ -14,6 +15,8 @@ import 'package:share_plus/share_plus.dart';
 import 'package:syncfusion_flutter_pdfviewer/pdfviewer.dart';
 import 'package:video_player/video_player.dart';
 
+import '../model/account_data.dart';
+import '../model/endpoint_data.dart';
 import '../routing/app_routes.dart';
 import '../share_intent/remote_file_ref.dart';
 import '../state/app/modules/settings/bloc/settings_cubit.dart';
@@ -22,6 +25,21 @@ import 'centered_leading.dart';
 import 'info_dialog.dart';
 import 'share_position_origin.dart';
 
+/// Nextcloud's `/index.php/core/preview` endpoint — returns a rasterized
+/// thumbnail for any file the server has a preview provider for (images,
+/// PDFs with the right backend, Office in some setups). Falls back to an
+/// HTTP 404 when no preview is available, which lets [CachedNetworkImage]
+/// trigger its `errorWidget`. Prefers `fileId` because the path variant
+/// is unreliable on some server configurations.
+String _ncPreviewUrl(RemoteFileRef remote, {int width = 1024}) {
+  final host = EndpointData().nextcloud().full();
+  final id = remote.fileId;
+  final selector = id != null
+      ? 'fileId=$id'
+      : 'file=${Uri.encodeQueryComponent(remote.path)}';
+  return 'https://$host/index.php/core/preview?$selector&x=$width&y=-1&a=1';
+}
+
 class FileViewer extends StatefulWidget {
   final String path;
   final bool openExternal;
@@ -482,26 +500,33 @@ class _FileViewerState extends State<FileViewer> {
     ),
   );
 
-  Widget _buildUnknownView() {
+  Widget _buildUnknownView() => Scaffold(
+    appBar: _appbar(showActionsMenu: false),
+    body: _buildUnknownPlaceholder(),
+  );
+
+  Widget _buildUnknownPlaceholder() {
     final theme = Theme.of(context);
     final descriptors = _availableActions();
-    return Scaffold(
+    final remote = widget.remoteFile;
-      appBar: _appbar(showActionsMenu: false),
+    final hasPreview = remote?.hasPreview == true;
-      body: ListView(
+    return ListView(
       padding: const EdgeInsets.symmetric(vertical: 24),
       children: [
         Padding(
           padding: const EdgeInsets.symmetric(horizontal: 24),
           child: Column(
             children: [
-                const Icon(Icons.insert_drive_file_outlined, size: 60),
+              _UnknownPreviewHeader(remoteFile: remote),
               const SizedBox(height: 16),
+              if (!hasPreview) ...[
                 Text(
                   'Vorschau nicht verfügbar',
                   style: theme.textTheme.titleMedium,
                   textAlign: TextAlign.center,
                 ),
                 const SizedBox(height: 6),
+              ],
               Text(
                 widget.path.split('/').last,
                 style: theme.textTheme.titleSmall?.copyWith(
@@ -527,7 +552,6 @@ class _FileViewerState extends State<FileViewer> {
           ),
         ),
       ],
-      ),
     );
   }
 
@@ -583,6 +607,50 @@ class _TextPayload {
   const _TextPayload({required this.content, required this.truncated});
 }
 
+/// Header for the "Vorschau nicht verfügbar" screen: tries to fetch the
+/// Nextcloud thumbnail and shows it mid-sized if available, otherwise
+/// falls back to the generic file icon.
+class _UnknownPreviewHeader extends StatelessWidget {
+  final RemoteFileRef? remoteFile;
+  const _UnknownPreviewHeader({required this.remoteFile});
+
+  static const double _previewSize = 180;
+
+  Widget _fallbackIcon() =>
+      const Icon(Icons.insert_drive_file_outlined, size: 60);
+
+  @override
+  Widget build(BuildContext context) {
+    final remote = remoteFile;
+    // Skip the probe outright when the server already told us there is no
+    // preview — saves an HTTP request that would 404 anyway.
+    if (remote == null || remote.hasPreview == false) return _fallbackIcon();
+    return SizedBox(
+      width: _previewSize,
+      height: _previewSize,
+      child: CachedNetworkImage(
+        httpHeaders: AccountData().authHeaders(),
+        imageUrl: _ncPreviewUrl(remote, width: 360),
+        fadeInDuration: Duration.zero,
+        fadeOutDuration: Duration.zero,
+        errorListener: (_) {},
+        placeholder: (_, _) =>
+            const Center(child: AppProgressIndicator.large()),
+        errorWidget: (_, _, _) => Center(child: _fallbackIcon()),
+        imageBuilder: (_, imageProvider) => ClipRRect(
+          borderRadius: BorderRadius.circular(8),
+          child: Image(
+            image: imageProvider,
+            fit: BoxFit.contain,
+            width: _previewSize,
+            height: _previewSize,
+          ),
+        ),
+      ),
+    );
+  }
+}
+
 class _MediaPlayer extends StatefulWidget {
   final String path;
   final bool isAudio;