Update and Read State of a Class using RiverPod Notifier

[Purus]

I have the below Riverpod annotation for the provider. I would like to update the values in one page and get the updated value in next page.

@riverpod
class UserCardSheetInfo extends _$UserCardSheetInfo {
  @override
  UserCardInputSheet build() => UserCardInputSheet();

  void updateIssuer(String value) {
    state.issuerKey = value;
  }

  void updateCard(String value) {
    state.setCardKey = value;
  }
}

class UserCardInputSheet {
  String _issuerKey = "";
  String _cardKey = "";

  String get issuerKey => _issuerKey;

  set issuerKey(String value) {
    _issuerKey = value;
  }

  String get cardKey => _cardKey;

  set setCardKey(String val) {
    _cardKey = val;
  }
}

I the first page, I am updating the value as below.

class _SelectableIssuersList extends ConsumerStatefulWidget {
  const _SelectableIssuersList();

  @override
  ConsumerState<_SelectableIssuersList> createState() => _SelectableCardsListState();
}

class _SelectableCardsListState extends ConsumerState<_SelectableIssuersList> {
  @override
  Widget build(BuildContext context) {

    return SomeWidget( 
             onClick: (newIssuer) => setState(() {               
               ref.watch(userCardSheetInfoProvider.notifier).updateIssuer(newIssuer);
             }),
     );
  }
}

In the next page, I am trying to read the updated value. But I am always getting an empty class without the values.

class _SelectableCardsList extends ConsumerStatefulWidget {
  const _SelectableCardsList();

  @override
  ConsumerState<_SelectableCardsList> createState() => _SelectableCardsListState();
}

class _SelectableCardsListState extends ConsumerState<_SelectableCardsList> {
  @override
  Widget build(BuildContext context) {
    List<Cards> cards = ref.read(cardsProvider).requireValue;
    
    // ====> Always Empty
    print(ref.watch(userCardSheetInfoProvider).issuerKey);

    return AnotherWidget();
  }
}

How should I be handling the value read/write using Riverpod?

[gdurandrexel]

Update the state, not a value inside the state, or the provider will not notify its listeners:

void updateCard(String value) {
    state = UserCardInputSheet(value);
}

Prefer using ref.watch in builders: List<Cards> cards = ref.watch(cardsProvider); to trigger a rebuild when the cardsProvider changes. No need for requireValue. It's usefull only for async providers, and anyway you don't want to use that in build() because it will throw when the provider is loading.

No need to use watch in handlers:

onClick: (newIssuer) => setState(() {               
               ref.read(userCardSheetInfoProvider.notifier).updateIssuer(newIssuer);
             })

And setState is useless here, since you do not update the state of your widget. If your widget depends on UserCardSheetInfo, watch it in build().

You may want to spend more time reading the riverpod doc.