Made by Surf 🏄♂️🏄♂️🏄♂️
A simple union with three states (loading, data, and error) based on sealed classes and ChangeNotifier. Used for delivering data to the UI layer, for example, using the Elementary library. The package includes the following classes:
A universal model for mapping basic UI states.
Can be used as internal replacement for [EntityState]. Unlike [EntityState]:
- Guarantees a non-zero result [T].
- Explicitly guarantees only 3 states: loading, content, error.
final _countryListState = UnionStateNotifier<Iterable<Country>>.loading();
Future<void> _loadCountryList() async {
final previousData = _countryListState.value.data;
// set property to loading state and use previous data for this state
_countryListState.loading(previousData);
try {
// await the result
final res = await model.loadCountries();
// set property to content state, use new data
_countryListState.content(res);
} on Exception catch (e) {
// set property to error state
_countryListState.failure(e, previousData);
}
}Presentation part builder for [ValueListenable] and [UnionState].
Note that a non-zero result [T] is only guaranteed for UnionStateContent. But not for load and fail.
// ......
@override
Widget build(IExampleWM wm) {
return Scaffold(
appBar: AppBar(),
body: UnionStateListenableBuilder<String>(
unionStateListenable: wm.dataState,
builder: (_, data) => Center(child: Text(data)),
loadingBuilder: (_, lastData) => Center(
child: Column(
mainAxisSize: MainAxisSize.min,
children: [
const CircularProgressIndicator(),
if (lastData != null) ...[
const SizedBox(height: 10),
Text('Last data: $lastData'),
],
],
),
),
failureBuilder: (_, exception, lastData) => Center(
child: Column(
mainAxisSize: MainAxisSize.min,
children: [
Text(exception.toString()),
if (lastData != null) ...[
const SizedBox(height: 10),
Text('Last data: $lastData'),
],
],
),
),
),
);
}
// ......A custom [ValueNotifier] that encapsulates the state of a union type. It provides methods to manage different states of data:
-[content]: Represents a state with successful content. -[failure]: Represents a state with an error and, optionally, previous data. -[loading]: Represents a state indicating that data is being loaded.
Can be used as internal replacement for [EntityStateNotifier]. Unlike [EntityState]:
- Guarantees a non-zero result [T].
- Explicitly guarantees only 3 states: loading, content, failure.
class ExampleModel extends ElementaryModel {
final _random = Random();
final dataState = UnionStateNotifier<String>.loading();
void initLoadData() {
dataState.loading(dataState.value.data);
Future.delayed(
const Duration(seconds: 1),
() {
_random.nextInt(10) < 8
? dataState.content('Loaded Data')
: dataState.failure();
},
);
}
}Add union_state to your pubspec.yaml file:
dependencies:
union_state: $currentVersion$At this moment, the current version of union_state is .
All notable changes to this project will be documented in this file.
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