CODEWITHSUNDEEP
flutterriverpod
rickb
rickb

Reputation: 671

Riverpod create StateNotifierProvider with state that extends another class

Case: New to riverpod - trying to migrade from regular flutter provider.

To create a StateNotifierProvider in riverpod one has to give it an instance that extends StateNotifier.

i.e.:

  class SomeModel extends StateNotifier {};
  StateNotifierProvider<SomeModel> someModelProvider = StateNotifierProvider<SomeModel>((ref) => someModel());

All well and good, if you have a simple model class. In my case, my model class is layered and extends a lower class:

  class SomeModel extends SomeLowerClass ...

I can't extend StateNotifier - I'm already extending some lower class. I can't use 'with' for either class because they both have constructors.

This seems like a an onerous limitation. Is there a way to create a provider that uses a model that extends another class besides 'StateNotifier', or use 'StateNotifier' in some other way other than by extending?

(puzzled, already...)

Upvotes: 1

Views: 1764

Answers (2)

rickb
rickb

Reputation: 671

Ok, the issue, of course, is my misconceptions.

@yeasin_shiekh is correct, I believe - what I'm (finally) getting is that StateNotifier contains an immutable object (not object extending StateNotifier). That immutable object can be constructed however, but the StateNotifier sends a notification when that object is replaced (not changed).

In my case, my model is a large, mutable object. So StateNotifier is not the correct thing to use. "ChangeNotifier" is what I need (and what I had used with flutter provider). The model then "extends" the ChangeNotifier (or you can use "with" if the model extends something else - my case) and you call "notifyListeners()" explicitly on changes, as before.

Getting the distinctions more clearly...

Upvotes: 0

EdwynZN
EdwynZN

Reputation: 5601

2 options:

SomeLowerClass should be extending StateNotifier

class SomeLowerClass extends StateNotifier {
   SomeLowerClass() : super(0); ///or whatever your state should be

   ///some other methods
}

class SomeModel extends SomeLowerClass {}

SomeLowerClass is an abstract class for you to implement

abstract class SomeLowerClass {
   void myMethod(); 
   ....
}

class SomeModel extends SomeLowerClass implements SomeLowerClass{
   @override
   void myMethod() {}
}

I think option 1 is what you really want to do

Upvotes: 0

Related Questions