WFFM: Custom validator does not appear (Sitecore 8.1 Update 1)

Question

I am implementing a custom validator for WFFM, to do so I followed the Sitecore documentation: https://doc.sitecore.net/web_forms_for_marketers/working_with_actions_and_validations/validations/walkthrough_create_and_assign_a_custom_fieldtype_validator

Valdation field, located at: /sitecore/system/Modules/Web Forms for Marketers/Settings/Validation/Key validator

Code:

public class KeyValidator : FormCustomValidator
{
    public KeyValidator()
    {
        ServerValidate += OnKeyValidate;
    }

    private void OnKeyValidate(object source, ServerValidateEventArgs args)
    {
        // some validation here...
    }
}

Assigned to "Single-Line Text" field However the new custom validator does not appear in the form designer:

Answer 1

Field type validator:

When you assign validations to a field, the changes you have made to the field affect all the forms on your website that use it. In addition to the default validations, you can also create your own custom field-type validations.

What you did, is the validation for the Field Type not for a specific form. You can create predefined validations which is documented here - https://doc.sitecore.net/web_forms_for_marketers/working_with_actions_and_validations/validations/set_up_and_create_a_formspecific_field_validation

Unfortunately this only allows you to put there regular expressions.

Suggested solution

I would create form verification which is called when the user submit the form.

After you created the new Form Verification item you can select this on the form.

The implementation should look like something like this:

namespace MyProject
{
    public class KeyValidator : WffmCheckAction
    {
        public override void Execute(ID formid, IEnumerable<ControlResult> fields, ActionCallContext actionCallContext = null)
        {
            // here is your validation
        }
    }
}