I am working on a custom control following the guide at "Create a custom form control sample" as an example. The sample is however quite lacking, since it does not show how to do validation the idiomatic Nintex Forms way.
As I have written about in another question, I am building an alternative List Lookup from control, where the user can choose to select nothing, even though the field is required.
What is the right approach to generate ASP.NET WebForms server side controls, add them to the page model, hook in validation controls, and have them work in a postback?
Note: I am using Nintex for SharePoint 2016 188.8.131.52 with SharePoint 2016.