Flutter: how to create a Singleton from an http request - http

Question

I want to declare a user object, that I will instantiate with an http request, and I want it to be global. How can I do it? With a Singleton? But how can I make this class also a Singleton? Or is there another way?
That is what I've done so far:
class User{
String username;
String password;
int id;
User({this.username, this.id});
factory User.fromJson(Map<String, dynamic> json){
return User(
username: json['name'],
id: json['id']
);
}
}
and then:
var user = await login(username, password, context);

Answer 1

In flutter, you should not make singletons. Instead, you should store it into a widget that exposes these data to all of its descendants.
Usually InheritedWidget
The reason being, with such architecture all the descendants are automatically aware of any change made to your "singleton".
A typical example would be the following:
#immutable
class User {
final String name;
User({this.name});
}
class Authentificator extends StatefulWidget {
static User currentUser(BuildContext context) {
final _AuthentificatorScope scope = context.inheritFromWidgetOfExactType(_AuthentificatorScope);
return scope.user;
}
final Widget child;
Authentificator({this.child, Key key}): super(key: key);
#override
_AuthentificatorState createState() => _AuthentificatorState();
}
class _AuthentificatorState extends State<Authentificator> {
#override
Widget build(BuildContext context) {
return _AuthentificatorScope(
child: widget.child,
);
}
}
class _AuthentificatorScope extends InheritedWidget {
final User user;
_AuthentificatorScope({this.user, Widget child, Key key}) : super(child: child, key: key);
#override
bool updateShouldNotify(_AuthentificatorScope oldWidget) {
return user != oldWidget.user;
}
}
which you have to instantiate like this:
new MaterialApp(
title: 'Flutter Demo',
builder: (context, child) {
return Authentificator(
child: child,
);
},
home: Home(),
);
and then use inside your pages like this:
#override
Widget build(BuildContext context) {
User user = Authentificator.currentUser(context);
...
}