What you need is a mediator to sit in between the textboxes and the checkboxes so you have only one place to write your code. A very good candidate for this job is the form itself. If you move all of the code from the checkboxes and textboxes that refers to the other and put it in the form's refresh you can accomplish this goal. However you still have the problem that if you add or remove any of these you must change the code in the form's refresh method.

There are ways to remove even that issue but they are beyond what could easily be discussed in a thread messsage.