Flutter shared_preferences save list<any_class> - flutter

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();
});
}
}