Dart dependency injection of a class with parameters - flutter

Question

I am trying to learn about dependency injection and trying to use it in Flutter/Dart. I have gone through the library get_it which I find very useful.
But I am having a doubt about the dependency injection in a specific situation.
If I have a Dart class with parameters like this one for example:
class MyClass(){
final String name;
MyClass({this.name})
....
....
}
In such a class, with parameters, It seems like I cannot use dependency injection? or at least the following using get_it will not work:
**** service_locator.dart ****
import 'package:get_it/get_it.dart';
GetIt locator = GetIt();
void setupLocator() {
locator.registerLazySingleton<MyClass>(() => MyClass());
}
This gives error on => MyClass()....since it is expecting a parameter.
How to do this kind of injection?.

Answer 1

You just pass the argument you want to MyClass(). You don’t have to do it inside setUpLocator(). Register the singleton, anywhere in your program, when you know what argument to pass.
For example, if you need to register a user object as a singleton, you’ll have to do it after the user logs in and all their info is available in order to properly instantiate your User class.

Answer 2

because it is a singleton you only need to call myClass.name = 'name' once, anywhere in your app and it will change everywhere.
example app:
class _MyHomePageState extends State<MyHomePage> {
#override
void initState() {
super.initState();
GetIt.instance.registerLazySingleton<MyClass>(()=> MyClass());
// Name from a future
get('https://jsonplaceholder.typicode.com/users').then((response){
if(response.statusCode==200) {
setState(() {
GetIt.I.get<MyClass>().name = jsonDecode(response.body)[0]['name'];
});
}
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Title'),
),
body: Container(
child: Center(
child: Text(GetIt.I.get<MyClass>().name),
),
),
);
}
}
class MyClass{
String name = '';
}
another way is that because it's built using a lazy builder, the MyClass object will only be built after the first locator.get<MyClass>() is called so you can prepare and get it from a static variable.

Answer 3

There is no issue passing a string into the constructor of your class. You only need access to the value you want to pass into the MyClass constructor. One way to do that is to get the value from another dependency. In this example, you can grab it from AppOptions.
import 'package:ioc_container/ioc_container.dart';
class MyClass {
final String name;
MyClass({required this.name});
}
class AppOptions {
String get myClassName => 'Bob';
}
void main(List<String> arguments) {
final builder = IocContainerBuilder()
..addSingletonService<AppOptions>(AppOptions())
..addSingleton(
(container) => MyClass(name: container<AppOptions>().myClassName));
final container = builder.toContainer();
final myClass = container<MyClass>();
print(myClass.name);
}
Grab the package here
This prints
Bob