useExistingSignal#

Function: useExistingSignal#

S useExistingSignal(S value, {List<Object?> keys = const <Object>[]})

Subscribes to an existing ReadonlySignal (or Signal) and returns it.

This is useful when you have a signal that is defined globally, inside a controller, or provided via a dependency injection framework (like provider, get_it, or riverpod), and you want to reactive-bind the HookWidget to rebuild whenever the signal emits a new value.

Parameters#

• value: The existing ReadonlySignal or Signal instance to subscribe to.
• keys: A list of objects to watch for changes. If any of the keys change, the hook is re-evaluated, unsubscribing from the old signal and subscribing to the new one.

Returns#

The same signal instance passed in value, allowing you to interact with it directly (e.g., read its .value or write to it if it is a mutable Signal).

Example#

import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';
import 'package:signals_hooks/signals_hooks.dart';

// A globally defined signal or one located in a service
final globalThemeMode = signal(ThemeMode.light);

class ThemeSelectorWidget extends HookWidget {
  const ThemeSelectorWidget({super.key});

  @override
  Widget build(BuildContext context) {
    // Bind to the existing global signal
    final themeMode = useExistingSignal(globalThemeMode);

    return SwitchListTile(
      title: Text('Dark Mode: ${themeMode.value == ThemeMode.dark ? "On" : "Off"}'),
      value: themeMode.value == ThemeMode.dark,
      onChanged: (isDark) {
        themeMode.value = isDark ? ThemeMode.dark : ThemeMode.light;
      },
    );
  }
}

References#

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

• signals_hooks
• useSignal (signals_hooks/hooks)
• useSignalValue (signals_hooks/hooks)
• useExistingSignal (signals_hooks/hooks)