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(callback) {
disposer.addStreamSubscription(input.onBlur.listen((_) {
callback(input.inputText);
}));
}