exists abstract method
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logic that depends on the existence or not of a provider won't be rerun; possibly causing your state to get out of date.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
bool exists(ProviderBase<Object?> provider);