validate method

  1. @override
String? validate(
  1. String input
)
override

A function that returns an error message string to display if the input s not pass a validation test and returns null otherwise.

Implementation

@override
String? validate(String input) {
  int l = input.length;

  if (l < min) {
    return "Please enter a value that is at least $min characters long.";
  }
  if (l > max) {
    return "Please enter a value that does not exceed $max characters in length.";
  }

  return null;
}