onResult method
Registers a listener (addListener) that will be invoked with the current Result (value).
Use the returned VoidCallback function to unsubscribe the listener (i.e. calls removeListener).
See also:
Implementation
@useResult
VoidCallback onResult(void Function(Result<T> result) listener) {
void listenerFunc() => listener(value);
addListener(listenerFunc);
return () => removeListener(listenerFunc);
}