addListener method
Adds a listener/callback that will be called when the property value changes
Implementation
@override
void addListener(void Function(T value) callback) {
if (listeners.contains(callback)) {
return;
}
if (listeners.isEmpty) {
// Since we don't clean the changed flag for properties that don't have
// listeners, we clean it the first time we add a listener to it
clearChanges();
rootViewModelInstance.addCallback(this);
}
listeners.add(callback);
}