CustomProviderListenable<InT, ValueT> class abstract

A ProviderListenable whose value is derived from transforming another ProviderListenable (source).

This is the base class for implementing custom variants of methods such as ProviderListenableSelect.select.

Usage

To use this class, you must implement the source. getter (the provider that is being transformed) and createTransformer (the object responsible for computing/holding the transformed state, see ProviderTransformer2).

The following example implements a variant of ProviderListenableSelect.select, where the callback returns a boolean instead of the selected value.

final class Where<T> extends CustomProviderListenable<T, T> {
  Where(this.source, this.where);

  @override
  final ProviderListenable<T> source;
  final bool Function(T previous, T value) where;

  @override
  _WhereTransformer<T> createTransformer() => _WhereTransformer<T>();
}

final class _WhereTransformer<T>
    extends SyncProviderTransformer2<T, T, Where<T>> {
  @override
  T initState() => sourceState.requireValue;

  @override
  void onEvent(
    AsyncResult<T> prev,
    AsyncResult<T> next,
  ) {
    if (listenable.where(prev.requireValue, next.requireValue)) {
      state = next;
    }
  }
}

extension<T> on ProviderListenable<T> {
  ProviderListenable<T> where(
    bool Function(T previous, T value) where,
  ) => Where<T>(this, where);
}

Used as ref.watch(provider.where((previous, value) => value > 0)).

See also:

Implemented types
Available extensions
Annotations
  • @publicInMisc

Constructors

CustomProviderListenable()

Properties

hashCode → int
The hash code for this object.
no setterinherited
listenable → ProviderListenable<ValueListenable<T>>

Available on ProviderListenable<T>, provided by the ProviderListenableListenable extension

Exposes a ValueListenable that tracks the state of this provider.
no setter
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
source → ProviderListenable<InT>
The source of this transformer.
no setter

Methods

createTransformer() → ProviderTransformer2<InT, ValueT, CustomProviderListenable<InT, ValueT>>
Creates the ProviderTransformer2 responsible for computing and holding the state of this CustomProviderListenable.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
select<OutT>(OutT selector(InT value)) → ProviderListenable<OutT>

Available on ProviderListenable<InT>, provided by the ProviderListenableSelect extension

Partially listen to a provider.
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited