Flutter shared_preferences save list<any_class>

Question

I tried to save a list to my shared preferences but the list isn't a String list it is a list of a special type class "todo". I tried it with ".cast<Todo>();", this worked with prefs.getStringList.... but dont work with prefs.setStringList. Here is a screenshot:

When I try to do prefs.setStringList("shoppingCard", _todos); it says: "The argument type 'List' can't be assigned to the parameter type 'List'."

This is the source code of the class todo:

    class Todo {
  Todo({required this.name, required this.checked});
  final String name;
  bool checked;
}

class TodoItem extends StatelessWidget {
  TodoItem({
    required this.todo,
    required this.onTap,
  }) : super(key: ObjectKey(todo));

  final Todo todo;
  final Function onTap;

  TextStyle? _getTextStyle(bool checked) {
    if (!checked) return null;

    return const TextStyle(
      color: Colors.black54,
      decoration: TextDecoration.lineThrough,
    );
  }

  @override
  Widget build(BuildContext context) {
    return ListTile(
      onTap: () {
        onTap(todo);
      },
      leading: CircleAvatar(
        child: Text(todo.name[0]),
      ),
      title: Text(todo.name, style: _getTextStyle(todo.checked)),
    );
  }
}

Answer 1

If you need to save list of custom class you need convert it to string. First change your class model to this:

class Todo {
  Todo({required this.name, required this.checked});
  final String name;
  bool checked;
  static Todo fromJson(Map<String, dynamic> json) {
    return Todo(name: json['name'], checked: json['checked']);
  }

  Map<String, dynamic> toJson() {
    return {
      'name': name,
      'checked': checked,
    };
  }
}

then for saving your list in SharedPreferences, try this:

var prefs = await SharedPreferences.getInstance();
prefs.setString('shoppingCard',
        jsonEncode({'data': _todos.map((e) => e.toJson()).toList()}));

and for getting it, try this:

var prefs = await SharedPreferences.getInstance();
String? str = prefs.getString('shoppingCard');
    if (str != null) {
      var result = (jsonDecode(str) as Map)['data'] as List;
      result.map((e) => Todo.fromJson(e)).toList();
    }

for example in you case, lets say we have list below:

List<Todo> _todos = [
    Todo(checked: false, name: 'test1'),
    Todo(checked: true, name: 'test2')
  ];

we add this list to SharedPreferences, like this:

Future<void> _addTodoItem(String name) async {
    var prefs = await SharedPreferences.getInstance();

    prefs.setString('shoppingCard',
        jsonEncode({'data': _todos.map((e) => e.toJson()).toList()}));
    _textFieldController.clear();
  }

and we get list from SharedPreferences, like this:

Future<void> _getodoItem(String name) async {
    var prefs = await SharedPreferences.getInstance();
    var value = prefs.getString('shoppingCard');
    if (value != null) {
      var result = (jsonDecode(value) as Map)['data'] as List;

      setState(() {
        _todos = result.map((e) => Todo.fromJson(e)).toList();
      });
    }
  }