Validation on extended fields UserDefinedForm - silverstripe

Question

I have made an extension on the UserDefinedForm (module userforms). This works well, but I cannot figure out how to set validation on this extra fields. This is (a part of) my code:
class UserDefinedPaymentForm_Controller extends UserDefinedForm_Controller {
private static $allowed_actions = array(
"finished",
"complete",
"error"
);
public function getFormFields() {
//Payment fields
$supported_methods = PaymentProcessor::get_supported_methods();
$gateways = array();
foreach ($supported_methods as $methodName) {
$methodConfig = PaymentFactory::get_factory_config($methodName);
$gateways[$methodName] = $methodConfig['title'];
}
$fields = parent::getFormFields();
$fields->add(new NumericField("PaymentAmount", _t('UserDefinedPaymentForm.PAYMENT_AMOUNT', 'Payment Amount')));
$fields->add(new Literalfield("literalfield", _t('UserDefinedPaymentForm.PAY', '<h2>Pay</h2>')));
$fields->add(new Literalfield("literalfield", _t('UserDefinedPaymentForm.PAY_INSTRUCTIONS', '<p>Choose your prefered payment method and click Pay:</p>')));
$fields->add(new DropdownField("PaymentMethod", _t('UserDefinedPaymentForm.PAYMENT_METHOD', 'Payment Method'), $gateways));
return $fields;
}
}
Now I want to validate the field PaymentAmount, the value of this field has to be 2 or more. How can I do this?

Answer 1

I would guess (I haven't tested this) your best bet is to create a subclass of UserFormValidator and override the php($data) method.
Then, in your UserDefinedPaymentForm_Controller, you will also need to override the Form method.
class PaymentAmountUserFormValidator extends UserFormValidator {
public function php($data) {
$result = parent::php($data);
if ($result === true) {
// verify your PaymentAmount here and return true or false, accordingly
}
return $result;
}
class UserDefinedPaymentForm_Controller {
...
public function Form()
{
$form = UserForm::create($this);
// Generate required field validator
$requiredNames = $this
->getController()
->Fields()
->filter('Required', true)
->column('Name');
$validator = new PaymentAmountUserFormValidator($requiredNames);
$form->setValidator($validator);
$this->generateConditionalJavascript();
return $form;
}
...
}