FormyValidator<T> class abstract

A base class for creating custom field validators.

The FormyValidator can be used with FieldControllers holding values of type T. It provides an interface to implement validation logic by overriding onValidate.

If you implement a custom validator, override the onValidate method to define your specific validation rules.

Properties

• message: An optional custom error message to display when invalid.

Example

class PositiveNumberValidator extends FormyValidator<int> {
  PositiveNumberValidator({super.message});

  @override
  ValidationResult onValidate(FieldController<int> controller) {
    final value = controller.value;
    return ValidationResult(
      key: 'positive',
      message: message,
      isValid: value != null ? value > 0 : true,
    );
  }
}

FieldController<int> field = FieldController(
  key: 'amount',
  validators: [PositiveNumberValidator()],
);

See also

• ValidationResult, which describes the outcome of validation.
• FieldController, which holds the field value to be validated.