Numery regularne tylko rzutki
RegExp _regExp = RegExp(r'^[0-9]+$');
_regExp.hasMatch(number);
Dead Dormouse
RegExp _regExp = RegExp(r'^[0-9]+$');
_regExp.hasMatch(number);
r'(^(?=.*\d))'
// For 6 to 20 use this:
r'(^(?=.*\d).{6,20}$)'need help whit code