How to get value from dynamic created textbox

Hello everyone,

I am trying to build an application in the Master Pages, and now I have encountered a problem where I got stuck.I
In my content page I create a dynamic table which includes text boxes that are filled with values from a list. I also have a Updatebutton where I want to check if the user has changed the value in the text box.

My problem is that I can not get any value from my text boxes.

Here is what my code look like at the moment:
//Page Load
protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsPostBack)
  ...