Sitecore Forms Custom field gives 400 bad request when trying to add to a form via the forms interface

Question

On Sitecore 9.2.0, I have created a custom field, based on the relevant tutorial (https://doc.sitecore.com/developers/92/sitecore-experience-manager/en/walkthrough--creating-a-custom-rating-element-with-property-editor.html).

When I try to add this field into a form via the Forms UI, I see in the network tab that the relevant API call fails with a status code of 400 (bad request). All OOTB fields work fine. Sitecore logs report absolutely nothing, event viewer reports absolutely nothing.

I am obviously missing something. Any insights on where to look?

Answer 1

It turns out that for the Form editor to work, all field type templates must have a standard values. By decompiling the DLL that contains the action for the API controller for the SPEAK interface of the form editor, I found that internally it runs a pipeline, and the first processor has an Assert that throws if the template for the field type does not have a (empty) standard values. Adding standard values made the error go away.

A bit more informative error than just 400 Bad Request would have been more helpful, methinks.

Answer 2

For anyone who is coming from Upgrade route

I upgraded Sitecore 8.2 to 9.2 via sitecore upgrade but couldn't use form fields - note that in my case I was able to see the form items both in Forms & Content editor but couldn't edit/save them(400-Bad request error while adding form fields). Following steps fixed it:

1. While upgrading the _Standard Value of Form template items aren't created properly and essentially the Forms pipeline needs the Standard Values. Got the templates from a fresh sitecore instance to fix it. The location in content tree is sitecore/templates/System/Forms
2. If you have custom processors interfering HttpRequest pipeline e.g. Custom MarkupProcessor, check them out if they are stopping the Form field rendering