dartfier library

Fine-grained reactivity for Flutter, built entirely on ChangeNotifier.

A Signal holds a value, a Computed derives one, an Effect runs a side effect and an Observer rebuilds a widget. Reading .value inside a tracked scope — an Observer builder, a Computed function or an Effect body — subscribes the reader to that value, so dependencies are discovered on every run instead of declared up front.

final Signal<int> count = Signal(0);
final Computed<int> doubled = Computed(() => count.value * 2);

count.value = 5;
print(doubled.value); // 10

A write settles in two phases: it first marks the reachable graph stale, waking nobody, and only then does each stale node recompute and notify — and only if its value actually changed. Reads are therefore always consistent, even in a diamond, and a derivation that lands on an equal value stops the cascade there.

Every reactive value is a ChangeNotifier implementing ValueListenable, so ValueListenableBuilder, Listenable.merge and any Flutter API taking a Listenable work without an adapter.

See also:

• Signal, the writable reactive value.
• Computed, a lazy value derived from other reactive values.
• ReadonlySignal, the read-only supertype of both.
• Effect, a side effect that reruns when what it read changes.
• Watch, a side effect on a tracked expression, skipping the first run.
• Observer, the widget that rebuilds on the values its builder reads.
• AsyncSignal, which brings asynchronous work into the graph.
• batch, which groups several writes into a single notification.

Classes

AsyncData<T>

Operation completed with value.

AsyncError<T>

Operation failed with error, optionally carrying the previous data.

AsyncIdle<T>

No operation started yet.

AsyncLoading<T>

Operation in flight, optionally carrying the previous data.

AsyncSignal<T>

A Signal holding the AsyncValue of an asynchronous operation.

AsyncValue<T>

The state of an asynchronous operation exposed as a synchronous value.

Computed<T>

A derived reactive value with automatic dependency tracking.

Effect

A reactive side effect with automatic dependency tracking.

Observer

A widget that rebuilds when any reactive value read in its builder changes.

ReadonlySignal<T>

A read-only view of a reactive value.

Signal<T>

A reactive value built on ChangeNotifier.

Watch<T>

A side effect on an auto-tracked expression, skipping the first run.

Extensions

ReadonlySignalSubscriptions on ReadonlySignal<T>

Side-effect subscriptions on any ReadonlySignal.

Functions

batch<T>(T run()) → T

Groups several writes into a single atomic update.

untracked<T>(T run()) → T

Runs run with dependency tracking suspended and returns its result.

Typedefs

EffectCleanup = void Function()

A cleanup callback registered by an Effect run.