Singleton with dependency injection in Dart

Question

Can anyone help me with using dependency injection on singleton? here is my code:

class SpaceController extends ChangeNotifier {
  final SpacesPersistence _persistence;

  static final SpaceController _instance = SpaceController._internal(persistence: null);
  factory SpaceController({required SpacesPersistence persistence}) {
    return _instance;
  }

  SpaceController._internal({required SpacesPersistence persistence}) : _persistence = persistence;
}



abstract class SpacesPersistence {
  Future<List<Entry>> getPath();

  Future<List<Entry>> getEntries(Entry? parent, [String? keyword]);

  Future<List<Connection>> getConnections([List<Entry>? entries]);

  Future<void> add(Entry entry);

  Future<void> remove(Entry entry);

  Future<void> update(Entry entry);

  Future<void> setPath(List<Entry> path);
}

This problem is that I want to inject the persistence variable, but _internal requires the argument and _persistence is not ready yet.

Add code for `SpacesPersistence`, and Are you using any library for dependency injection ? — Alex Sunder Singh, Feb 19 '23 at 17:41
Does this answer your question? [In Dart, is it possible to pass an argument in a singleton?](https://stackoverflow.com/questions/56088670/in-dart-is-it-possible-to-pass-an-argument-in-a-singleton) — user18309290, Feb 19 '23 at 17:58
not really it doesn't use dependency injection, I don't use any library — Moel, Feb 19 '23 at 18:02

score 0 · Answer 1 · answered Feb 19 '23 at 18:05

0

Try with passing new instance in _instance. Here SpacesPersistenceImpl is a class which implements SpaceController

class SpaceController extends ChangeNotifier {
  final SpacesPersistence _persistence;

  static final SpaceController _instance = SpaceController._internal(persistence: SpacesPersistenceImpl());
  factory SpaceController() {
    return _instance;
  }

  SpaceController._internal({required SpacesPersistence persistence}) : _persistence = persistence;
}

answered Feb 19 '23 at 18:05

Alex Sunder Singh

2,378
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I understand, this means i have to define in class, the Persistance implementation I want to use, am I wrong? – Moel Feb 20 '23 at 10:54
Yea, you have to define a class `SpacesPersistenceImpl` – Alex Sunder Singh Feb 20 '23 at 10:56

score 0 · Answer 2 · answered Feb 19 '23 at 21:59

0

I simply grab a RiverPod provider, which gives me lazy initialization, discoverability as a singleton, and dependency injection via overrides for mocking during testing. Details at http://riverpod.dev/

answered Feb 19 '23 at 21:59

Randal Schwartz

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So no way to do it without an extra library? I feel like using riverpod is some kind of over engineering for a simple app – Moel Feb 20 '23 at 07:04
It actually scales downward to the small end fairly nicely. – Randal Schwartz Feb 20 '23 at 08:54

Singleton with dependency injection in Dart

2 Answers2