I am building a custom config element by extending JMeter SDK. I have achieved most of my desired functionality. Last piece is to set a computed value to a JMeter variable so that it can be used in HTTP Samplers. I looked at existing components implementation - Test Plan and User Defined Variables, but could not figure steps to set a variable value. Argument and Arguments classes are the closest I could get, but not answering the question.
In my config element, I am extending AbstractConfigGui to create GUI components and AbstractTestElement to glue UI and Data.
My code is not available on public domain, but can share snippets if required for further clarifications.