Base Newsletter Action Class
Ninja Forms THREE comes with a Base Newsletter Action Class, NF_Abstracts_ActionNewsletter, which should be extended by newsletter integrations and includes support for basic newsletter action settings.
The basic newsletter action settings include a list select setting and a dynamic number of field mapping settings, conditionally displayed based on the selected list.
For this functionality to be inherited, the base class requires the get_lists() method, which is used to dynamically create list selector options, as well as field mapping settings for each list.
The get_lists() method should return an array of list options, each with an array of field options.
Refreshable List and List Fields
In addition to dynamically creating list selector options, the Base Newsletter Action Class utilizes the get_lists() method with a WordPress AJAX Action to re-populate the select options within the builder. The base class also provides basic caching functionality for getting lists and dumps the cache when updating from within the builder.