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rodydavis/signals.dart ★9999⑂99

Type: SignalEffect

API reference and details for SignalEffect from signals.dart.

SignalEffect#

Kind: class  |  Package: package:signals_flutter

Class: SignalEffect#

A widget that enables executing scoped reactive side-effects inline within the widget tree.

SignalEffect (and its direct type alias SignalListener) allows you to run side-effects (such as showing snackbars, opening dialogs, navigating, or logging metrics) in response to signal updates, without triggering rebuilds of the child widget tree.

The effect callback runs immediately on mount and dynamically tracks any signals accessed within its scope. The underlying subscription is automatically disposed when this widget is removed from the tree. You can optionally return a cleanup function (e.g. void Function()) to run before the next execution or when the widget is disposed.

Dialog and Snackbar Trigger Example# 

final count = signal(0);

class SnackBarTrigger extends StatelessWidget {
  const SnackBarTrigger({super.key});

  @override
  Widget build(BuildContext context) {
    return SignalEffect(
      effect: (context) {
        // Triggers whenever 'count' updates:
        if (count.value >= 10) {
          ScaffoldMessenger.of(context).showSnackBar(
            SnackBar(content: Text('Limit reached: ${count.value}!')),
          );
        }
        // Optional: return cleanup callback
        return () => print('Cleaning up effect');
      },
      child: ElevatedButton(
        onPressed: () => count.value++,
        child: const Text('Increment and Watch'),
      ),
    );
  }
}

Important

Do not perform synchronous state changes or trigger widget rebuilds directly inside the effect callback to prevent infinite reactive loops.

Members of SignalEffect#

Member Type Signature Description
SignalEffect constructor dart SignalEffect({dynamic Function(BuildContext context)? effect, @Deprecated('Use effect instead') void Function(BuildContext context)? callback, required this.child, this.debugLabel, super.key}) Creates a SignalEffect widget.
effect method dart dynamic Function(BuildContext context) effect Gets the effect callback to run inside the reactive effect.
child field dart Widget child The child widget to render.
debugLabel field dart String? debugLabel Optional debug label for the effect.
createState method dart State createState()

References#

The SignalEffect type is referenced and used in the following pages: