select method
Handles a change in the selection.
Implementation
@override
void select(T value, bool selected) {
if (selected) {
if (_max != null && _values.length >= _max) {
return;
}
_values.add(value);
} else {
if (_values.length <= _min) {
return;
}
_values.remove(value);
}
notifyListeners();
}