subscribe method
Subscribes to changes in the beacon returns a function that can be called to unsubscribe
Implementation
VoidCallback subscribe(void Function(T) callback, {bool startNow = false}) {
listener() => callback(_value);
final effectClosure = EffectClosure(listener);
listeners.add(effectClosure);
if (startNow) {
listener();
}
return () => listeners.remove(effectClosure);
}