validate method

@override String? validate(String? value)

Implementation

@override
String? validate(String? value) {
  if (additionalValidator != null) {
    final result = additionalValidator!(value);
    if (result != null) return result;
  }
  if (value == null || value.isEmpty) {
    return 'Please enter a number';
  }
  final number = int.tryParse(value);
  if (number == null) {
    return 'Please enter a valid number';
  }
  if (minValue != null && number < minValue!) {
    return 'Number must be at least $minValue';
  }
  if (maxValue != null && number > maxValue!) {
    return 'Number must be at most $maxValue';
  }
  return null;
}