exists method

@override bool exists(ProviderBase<Object?> provider)

Determines whether a provider is initialized or not.

Writing logic that conditionally depends on the existence of a provider is generally unsafe and should be avoided. The problem is that once the provider gets initialized, logic that depends on the existence or not of a provider won't be rerun; possibly causing your state to get out of date.

But it can be useful in some cases, such as to avoid re-fetching an object if a different network request already obtained it:

final fetchItemList = FutureProvider<List<Item>>(...);

final fetchItem = FutureProvider.autoDispose.family<Item, String>((ref, id) async {
  if (ref.exists(fetchItemList)) {
    // If `fetchItemList` is initialized, we look into its state
    // and return the already obtained item.
    final itemFromItemList = await ref.watch(
      fetchItemList.selectAsync((items) => items.firstWhereOrNull((item) => item.id == id)),
    );
    if (itemFromItemList != null) return itemFromItemList;
  }

  // If `fetchItemList` is not initialized, perform a network request for
  // "id" separately

  final json = await http.get('api/items/$id');
  return Item.fromJson(json);
});

Implementation

@override
bool exists(ProviderBase<Object?> provider) => _container.exists(provider);