I have been using shared_preferences to create and write in Json Files. The Problem i facing is i dont know how to create a Json Array and a List in shared_preferences.
I want to save and read a Json List.
read(String key) async {
final prefs = await SharedPreferences.getInstance();
return json.decode(prefs.getString(key));
}
save(String key, value) async {
final prefs = await SharedPreferences.getInstance();
prefs.setString(key, json.encode(value));
}
remove(String key) async {
final prefs = await SharedPreferences.getInstance();
prefs.remove(key);
}
} ```
Example on DartPad.
Save a list to SharedPreferences with setStringList:
const String key = "users";
List<User> users = [User(name: "tester")];
List<String> jsonList = users.map((user) => user.toJson()).toList();
SharedPreferences prefs = await SharedPreferences.getInstance();
prefs.setStringList(key, jsonList);
Read a list from SharedPreferences with getStringList:
jsonList = prefs.getStringList(key);
users = jsonList.map((json) => User.fromJson(json)).toList();
The user class with json convert: JSON and serialization
class User {
String name;
int age;
User({
this.name,
this.age,
});
factory User.fromJson(String str) => User.fromMap(json.decode(str));
String toJson() => json.encode(toMap());
factory User.fromMap(Map<String, dynamic> json) => User(
name: json["name"],
age: json["age"],
);
Map<String, dynamic> toMap() => {
"name": name,
"age": age,
};
}
Just map your json array to List<String> and after you can use the setStringList function provided in shared_preferences.dart
/// Saves a list of strings [value] to persistent storage in the background.
///
/// If [value] is null, this is equivalent to calling [remove()] on the [key].
Future<bool> setStringList(String key, List<String> value) =>
_setValue('StringList', key, value);
