MVC - Send Info From Modal Popup to Controller

Hi so I am new to MVC. 

 

So in my View I have a button that brings up a modal, in that model I have a textbox. I would like that data from the textbox to be sent to the controller via the submit button in the modal. That data must then be sent into a .txt file via the controller. 

 

Using the @using (Html.BeginForm("Controller", "Function", FormMethod.Post)) method. 

 

If I use a textbox directly from the view and send the data to the controller it works, but it just won't work from the modal.

 

Also trying to avoid using AJAX as I have never used it before. 

 

Please help!

 

Thanks so much