如何使用 dart/flutter 中的共享首选项保存和获取列表列表

Question

I have been trying to save a list of lists using shared preferences in dart. For example, I have a list List data = [["dave","21","M"],["steven","22","F"]] and I am trying to save and load as it is but app keeps throwing Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'List<String>'

I have tried converting the 2d list into a list using List new_data = data.expand((i) => i).toList(); and then saving it. But still, the exception persists even though it is a list containing only strings.

Answer 1

We can use jsonEncode and jsonDecode() to get the list out:

import 'package:shared_preferences/shared_preferences.dart';

List data = [["dave","21","M"],["steven","22","F"]];

handleData() async {
  var prefs = await SharedPreferences.getInstance();
  prefs.setString('key', jsonEncode(data)); // Encode the list here
  print(jsonDecode(prefs.getString('key'))); // Decode then print it out
}