flutter add value to list - flutter

Question

i set object like this : {"name":"alex","code":"123"}
into sharedPrefrence Calss A:
var resBody = {};
resBody["name"] = name.text;
resBody["code"] = pass.text;
str = json.encode(resBody);
print(str);
SharedPreferences prefs = await SharedPreferences.getInstance();
prefs.setString("list_customer", str);
and when get this sharedPrefrence in another class
add value of shared to the list Class B:
customer = (prefs.getString('list_customer'));
Map<String, dynamic> user = jsonDecode(customer);
_customer.nameFamily = user['name'];
_customer.code = user['code'];
_list.add(_customer);
and i want to know how can i set new value of shared into the previous list like this :
[{"name":"alex","code":"123"},{"name":"john","code":"128"}]

Answer 1

To store multiple customers, you need a List not Map.
Declare a List
List<Map<String, dynamic>> customers = [];
Add object(s) to the list
final customer = {
"name": name.text,
"code": pass.text,
};
customers.add(customer);
Stringfy (encode) customers list
final customersString = json.encode(customers);
Store encoded customers list
SharedPreferences prefs = await SharedPreferences.getInstance();
prefs.setString("list_customer", customersString);
Let's say you store one customer, and now you need to store another.
we get customers list first, then we decode it
String customersString = await prefs.getString('list_customer');
final customers = json.decode(customersString);
Add the new object to the list (previous step #2)
customers.add({
"name": 'Amir',
"code": 'SWF2022',
});
Repeat step #3 and #4.
Good luck

Answer 2

Check example below
Future saveGetValues() async {
const key = 'list_customer';
var list = <Map<String, String>>[];
list.add(createValue('name1', 'code2'));
//save first time
save(key, list);
list = await getValue<List<Map<String, String>>>(key); //here your saved list
//add second value
list.add(createValue('name2', 'code2'));
save(key, list);
list = await getValue<List<Map<String, String>>>(key); //here your saved list with two items
}
Map<String, String> createValue(String name, String code) {
final resBody = <String, String>{};
resBody["name"] = name;
resBody["code"] = code;
return resBody;
}
Future save(String key, dynamic value) async {
final prefs = await SharedPreferences.getInstance();
prefs.setString(key, jsonEncode(value));
}
Future<T> getValue<T>(String key) async {
final prefs = await SharedPreferences.getInstance();
return json.decode(prefs.getString(key)) as T;
}