getAll method
Implementation
@override
Future<List<String>> getAll() async {
await init();
var items = <String>[];
var keys = _prefs!
.getKeys()
.where((element) => element.startsWith(_prefix))
.toList();
for (var key in keys) {
var item = await read(key);
if (item != null) {
items.add(item);
}
}
return items;
}