DISCONTINUED

This package has been integrated (and improved) into Flutter Data

---

data_state

Easily produce and consume loading/error/data states in your application.

DataState is a StateNotifier-based alternative to AsyncSnapshot.

• Produce events from DataStateNotifier, Future, Stream, RxDart ValueStream
• Consume events through DataStateNotifier, Stream

👩🏾‍💻 Usage

Consuming state

Flutter example:

(Note: This example depends on flutter_data_state which is a separate package)

@overrideWidgetbuild(BuildContext context) {
returnDataStateBuilder<List<Post>>(
notifier: () => repo.watchPosts(),
builder: (context, state, notifier, _) {
returnColumn(
children: [
if (state.isLoading)
CircularProgressIndicator(),
if (state.hasException)
ExceptionWidget(state.exception),
if (state.hasModel)
ShowPost(state.model),
],
);
}
);
}

The notifier features a reload function, useful to restart a data loading cycle. It can be combined with a gesture detector or reloader widget:

Example 1:

GestureDetector(
onTap: () => notifier.reload(), // will trigger a rebuild with isLoading = true
child: _child,
)

Example 2:

RefreshIndicator(
onRefresh: notifier.reload,
child: _child,
),

Future & Stream input support

This package exposes an extension on Future<T> Function() called asDataNotifier.

It allows to turn any future into a DataStateNotifier callback to leverage caching and reloading capabilities.

Example 1:

final notifier = (() => future).asDataNotifier;

Example 2:

final notifier = (() {
if (Random().nextInt(10) >4) {
returnFuture<String>.error('Error!');
}
returnFuture.delayed(
Duration(seconds:1),
() =>'HELLO RANDOM: ${Random().nextInt(100)}!',
);
}).asDataNotifier;

Same for Streams and ValueStreams:

final notifier = (() => stream).asDataNotifier;

Consuming streams

Want to consume events via streams?

DataStateNotifier actually exposes an RxDart ValueStream:

@overrideWidgetbuild(BuildContext context) {
final stream = repo.watchPosts().stream;
returnStreamBuilder<List<Post>>(
initial: stream.value,
stream: stream,
builder: (context, snapshot) {
// snapshot as usual
}
);
}

This is the anatomy of an immutable DataState object:

final state =DataState({
T model,
bool isLoading =false,
Object exception,
StackTrace stackTrace,
});

🎸 Producing state

Example:

DataStateNotifier<List<Post>> watchPosts() {
final notifier =DataStateNotifier<List<Post>>(
DataState(model:getLocalPosts()),
reload: (notifier) async {
notifier.state = notifier.state.copyWith(isLoading:true);
try {
notifier.data =awaitloadPosts();
} catch (error, stackTrace) {
notifier.data = notifier.data.copyWith(exception: error, stackTrace: stackTrace);
}
},
);
// kick off cyclereturn notifier..reload();
}

The DataStateNotifier constructor takes:

• state as the first positional argument
• reload and onError as optional named arguments

⁉ FAQ

Why is DataState not a freezed union?

This would allow us to do the following destructuring:

state.when(
data: (data) =>Text(data),
loading: () =>constCircularProgressIndicator(),
error: (error, stackTrace) =>Text('Error $error'),
);

This turns out to be impractical in data-driven Flutter apps as there are cases where we need to render loading/error messages in addition to data – not instead of data.

Does DataStateNotifier depend on Flutter?

No. It can used with pure Dart.

➕ Collaborating

Please use Github to ask questions, open issues and send PRs. Thanks!

📝 License

See LICENSE