SignalBuilder class

A premium, surgical builder widget that rebuilds locally on signal changes.

SignalBuilder tracks any signals read dynamically within its builder callback and automatically subscribes to them. When any of these signals update, only the SignalBuilder is rebuilt, preventing costly rebuilds of the surrounding widget subtree.

This widget provides predictable, immediate, and memory-safe subscription management, automatically tearing down all active signal subscriptions when the builder is unmounted.

Surgical Counter Example

final count = signal(0);

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Counter')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Text('This static text never rebuilds!'),
            const SizedBox(height: 20),
            // Only this specific Text widget rebuilds when 'count' changes:
            SignalBuilder(
              builder: (context) => Text(
                'Count: ${count.value}',
                style: Theme.of(context).textTheme.headlineMedium,
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => count.value++,
        child: const Icon(Icons.add),
      ),
    );
  }
}

Tip

Keep SignalBuilder widgets as small and leaf-level as possible in your tree to maximize rendering performance.

Inheritance

Available extensions

StatelessWidgetConvertWidgetExtension

Constructors

SignalBuilder({Key? key, required Widget builder(BuildContext context), List<ReadonlySignal> dependencies = const []}): Creates a SignalBuilder widget.
const

Properties

builder → Widget Function(BuildContext context): The widget to rebuild when any signals change.
final
dependencies → List<ReadonlySignal>: List of optional dependencies to watch.
final
hashCode → int: The hash code for this object.
no setterinherited
key → Key?: Controls how one widget replaces another widget in the tree.
finalinherited
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited

Methods

build(BuildContext context) → Widget: Describes the part of the user interface represented by this widget.
override
createElement() → StatelessElement: Creates a StatelessElement to manage this widget's location in the tree.
inherited
debugDescribeChildren() → List<DiagnosticsNode>: Returns a list of DiagnosticsNode objects describing this node's children.
inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void: Add additional properties associated with the node.
inherited
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) → DiagnosticsNode: Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.
inherited
toSignalWidget() → SignalWidget: Available on StatelessWidget, provided by the StatelessWidgetConvertWidgetExtension extension
Converts this StatelessWidget to a SignalWidget.
toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) → String: A string representation of this object.
inherited
toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug, int wrapWidth = 65}) → String: Returns a string representation of this node and its descendants.
inherited
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String: Returns a one-line detailed description of the object.
inherited
toStringShort() → String: A short, textual description of this widget.
inherited

Operators

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