AsyncValue<T> class
Null safety
An utility for safely manipulating asynchronous data.
By using AsyncValue, you are guaranteed that you cannot forget to handle the loading/error state of an asynchronous operation.
It also expose some utilities to nicely convert an AsyncValue to
a different object.
For example, a Flutter Widget may use when
to convert an AsyncValue
into either a progress indicator, an error screen, or to show the data:
/// A provider that asynchronously expose the current user
final userProvider = StreamProvider<User>((_) async* {
// fetch the user
});
class Example extends ConsumerWidget {
@override
Widget build(BuildContext context, WidgetRef ref) {
final AsyncValue<User> user = ref.watch(userProvider);
return user.when(
loading: () => CircularProgressIndicator(),
error: (error, stack) => Text('Oops, something unexpected happened'),
data: (value) => Text('Hello ${user.name}'),
);
}
}
If a consumer of an AsyncValue does not care about the loading/error
state, consider using value
to read the state:
Widget build(BuildContext context, WidgetRef ref) {
// reads the data state directly – will be throw during loading/error states
final User user = ref.watch(userProvider).value;
return Text('Hello ${user.name}');
}
See also:
- FutureProvider and StreamProvider, which transforms a Future into an AsyncValue.
- AsyncValue.guard, to simplify transforming a Future into an AsyncValue.
- Implementers
- Available Extensions
- Annotations
Constructors
- AsyncValue.data(T value)
-
Creates an AsyncValue with a data.
constfactory
- AsyncValue.error(Object error, {StackTrace? stackTrace})
-
Creates an AsyncValue in error state.
constfactory
- AsyncValue.loading()
-
Creates an AsyncValue in loading state.
constfactory
Properties
- hashCode → int
-
The hash code for this object.
read-onlyinherited
- runtimeType → Type
-
A representation of the runtime type of the object.
read-onlyinherited
Methods
-
noSuchMethod(
Invocation invocation) → dynamic -
Invoked when a non-existent method or property is accessed.
inherited
-
toString(
) → String -
A string representation of this object.
inherited
Operators
-
operator ==(
Object other) → bool -
The equality operator.
inherited
Static Methods
-
guard<
T> (Future< T> future()) → Future<AsyncValue< T> > - Transforms a Future that may fail into something that is safe to read.