validate method

@nonVirtual String? validate(Map<String, FormFieldState> fields)

Validates the form field against its validation rules.

• fields A map of form field states for cross-field validation.

Returns an error message if validation fails, otherwise returns null.

Implementation

@nonVirtual
String? validate(Map<String, FormFieldState> fields) {
  for (final rule in rules) {
    if (!rule.validate(value, fields)) {
      return rule.message(label);
    }
  }
  return null;
}