AsyncValue<T> class abstract

A 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 exposes 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 exposes 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: (user) => Text('Hello ${user.name}'),
    );
  }
}

If a consumer of an AsyncValue does not care about the loading/error state, consider using value/valueOrNull to read the state:

Widget build(BuildContext context, WidgetRef ref) {
  // Reading .value will be throw during error and return null on "loading" states.
  final User user = ref.watch(userProvider).value;

  // Reading .value will be throw both on loading and error states.
  final User user2 = ref.watch(userProvider).requiredValue;

  ...
}

Constructors

AsyncValue.data(T value): Creates an AsyncValue with a data.
const

factory
AsyncValue.error(Object error, StackTrace stackTrace): Creates an AsyncValue in the error state.
const

factory
AsyncValue.loading(): Creates an AsyncValue in loading state.
const

factory

Properties

asData → AsyncData<T>?: Available on AsyncValue<T>, provided by the AsyncValueX extension
Upcast AsyncValue into an AsyncData, or return null if the AsyncValue is an AsyncLoading/AsyncError.
no setter
asError → AsyncError<T>?: Available on AsyncValue<T>, provided by the AsyncValueX extension
Upcast AsyncValue into an AsyncError, or return null if the AsyncValue is an AsyncLoading/AsyncData.
no setter
error → Object?: The error.
no setter
hasError → bool: Available on AsyncValue<T>, provided by the AsyncValueX extension
Whether error is not null.
no setter
hashCode → int: The hash code for this object.
no setteroverride
hasValue → bool: Whether value is set.
no setter
isLoading → bool: Whether some new value is currently asynchronously loading.
no setter
isRefreshing → bool: Available on AsyncValue<T>, provided by the AsyncValueX extension
Whether the associated provider was forced to recompute even though none of its dependencies has changed, after at least one value/error was emitted.
no setter
isReloading → bool: Available on AsyncValue<T>, provided by the AsyncValueX extension
Whether the associated provider was recomputed because of a dependency change (using Ref.watch), after at least one value/error was emitted.
no setter
requireValue → T: Available on AsyncValue<T>, provided by the AsyncValueX extension
If hasValue is true, returns the value. Otherwise if hasError, rethrows the error. Finally if in loading state, throws a StateError.
no setter
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited
stackTrace → StackTrace?: The stacktrace of error.
no setter
value → T?: The value currently exposed.
no setter
valueOrNull → T?: Available on AsyncValue<T>, provided by the AsyncValueX extension
Return the value or previous value if in loading/error state.
no setter

Methods

copyWithPrevious(AsyncValue<T> previous, {bool isRefresh = true}) → AsyncValue<T>: Clone an AsyncValue, merging it with previous.
map<R>({required R data(AsyncData<T> data), required R error(AsyncError<T> error), required R loading(AsyncLoading<T> loading)}) → R: Perform some action based on the current state of the AsyncValue.
mapOrNull<R>({R? data(AsyncData<T> data)?, R? error(AsyncError<T> error)?, R? loading(AsyncLoading<T> loading)?}) → R?: Available on AsyncValue<T>, provided by the AsyncValueX extension
Perform some actions based on the state of the AsyncValue, or return null if the current state wasn't tested.
maybeMap<R>({R data(AsyncData<T> data)?, R error(AsyncError<T> error)?, R loading(AsyncLoading<T> loading)?, required R orElse()}) → R: Available on AsyncValue<T>, provided by the AsyncValueX extension
Perform some actions based on the state of the AsyncValue, or call orElse if the current state was not tested.
maybeWhen<R>({bool skipLoadingOnReload = false, bool skipLoadingOnRefresh = true, bool skipError = false, R data(T data)?, R error(Object error, StackTrace stackTrace)?, R loading()?, required R orElse()}) → R: Available on AsyncValue<T>, provided by the AsyncValueX extension
Switch-case over the state of the AsyncValue while purposefully not handling some cases.
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
toString() → String: A string representation of this object.
override
unwrapPrevious() → AsyncValue<T>: The opposite of copyWithPrevious, reverting to the raw AsyncValue with no information on the previous state.
when<R>({bool skipLoadingOnReload = false, bool skipLoadingOnRefresh = true, bool skipError = false, required R data(T data), required R error(Object error, StackTrace stackTrace), required R loading()}) → R: Available on AsyncValue<T>, provided by the AsyncValueX extension
Performs an action based on the state of the AsyncValue.
whenData<R>(R cb(T value)) → AsyncValue<R>: Available on AsyncValue<T>, provided by the AsyncValueX extension
Shorthand for when to handle only the data case.
whenOrNull<R>({bool skipLoadingOnReload = false, bool skipLoadingOnRefresh = true, bool skipError = false, R? data(T data)?, R? error(Object error, StackTrace stackTrace)?, R? loading()?}) → R?: Available on AsyncValue<T>, provided by the AsyncValueX extension
Perform actions conditionally based on the state of the AsyncValue.

Operators

operator ==(Object other) → bool: The equality operator.
override

Static Methods

guard<T>(Future<T> future(), [bool test(Object)?]) → Future<AsyncValue<T>>: Transforms a Future that may fail into something that is safe to read.