Flutter: Future.then() never getting invoked - asynchronous

Question

I'm currently playing around with Futures in flutter. I've some async functions that return a Future object. I register a Listener on the Future object with then(), so that I can update the ui as soon as the value comes in.
But the result is empty, because then() returns before all notes are loaded from the file system.
Future<List<Note>> loadNotes() async {
NoteService().findAll().then((result) {
result.forEach((note) => print(note.title)); //not printing -> result is emtpty...
});
}
//NoteService class
Future<List<Note>> findAll() async {
return noteRepository.findAll();
}
//NoteRepository class
#override
Future<List<Note>> findAll() async {
final Directory dir = await directory;
dir.list().toList().then((List<FileSystemEntity> list) async {
List<String> paths = List();
list.forEach((entity) => paths.add(entity.path));
List<File> _files = List();
paths.forEach((path) => _files.add(File(path)));
List<Note> notes = await _extractNotes(_files);
return Future.value(notes);
});
return Future.value(List());
}
Future<List<Note>> _extractNotes(List<File> _files) async {
List<Note> notes = List();
_files.forEach((file) {
String content = file.readAsStringSync();
print('content: ' + content); //this is getting printed correctly to the console
Map<String, dynamic> a = jsonDecode(content);
if(a.containsKey('codeSnippets')) {
notes.add(SnippetNoteEntity.fromJson(jsonDecode(content)));
} else {
notes.add(MarkdownNoteEntity.fromJson(jsonDecode(content)));
}
});
return Future.value(notes);
}