useExistingSignal<T, S extends ReadonlySignal<T>> function

S useExistingSignal<T, S extends ReadonlySignal<T>>(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;
      },
    );
  }
}

Implementation

S useExistingSignal<T, S extends ReadonlySignal<T>>(
  S value, {
  /// A list of objects to watch for changes.
  ///
  /// If any of the keys change, the hook will be re-evaluated.
  List<Object?> keys = const <Object>[],
}) {
  return use(SignalHook<T, S>(value, keys: keys));
}