CODEWITHSUNDEEP
flutterdart
Moel
Moel

Reputation: 59

Singleton with dependency injection in Dart

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.

Upvotes: 0

Views: 1063

Answers (2)

Randal Schwartz
Randal Schwartz

Reputation: 44186

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/

Upvotes: 0

Alex Sunder Singh
Alex Sunder Singh

Reputation: 2584

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;
}

Upvotes: 0

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