registerOnChange method
Set the function to be called when the control receives a change event.
NOTE: This function should only be called by view (i.e. user-initiated) changes. Incorrect implementation of registerOnChange will cause issues such as the control incorrectly being marked as dirty from a model update.
Implementation
@override
void registerOnChange(ChangeFunction<dynamic> callback) {
_disposer.addStreamSubscription(onChange.listen(callback));
}