registerListener method
Register listener
for key
with the value
injected for the listener.
The listener
will still be called when you delete the key
with the injected value
as null.
This listener will be added to the list of registered listeners for that key
.
Implementation
void registerListener({
required String key,
required ValueChanged<String?> listener,
}) {
_listeners[key] = [..._listeners[key] ?? [], listener];
}