I'm not sure what your trying to do is even possible. However, what you could do is have a Parent Form
which contains your ideal Interface. Within this Parent you could create an Event Handler
that is listening for a response.
Then when it comes to that Textbox
it actually creates a Child Form
or Page
. Which they can input their value into. Then the page automatically closes, which then the Event Handler
will already know the change for you to manipulate with the rest of your Logic.
As mentioned above, normally you would go to another page. I don't know if my solution is viable, but it does accomplish your goal. I'd recommend possibly refactoring your interface so that it makes it slightly more elegant. That way your logic handles it more elegant as well.
Hope that helps.