setValid method
Implementation
void setValid(String newValue) {
if (newValue.length == 3) {
if (newValue.contains("/")) {
_cardValid = newValue.substring(0, 2);
} else {
_cardValid = newValue.substring(0, 2) + "/" + newValue.substring(2);
}
} else {
_cardValid = newValue;
}
notifyListeners();
}