title: How to make a listbox in c# not duplicate items on button click?
body: <p>Well, i'm using ASP.NET c# listbox. I also have a button, the idea is the following: whenever I click the button an item x has to be shown in the listbox. However, I click the button many times, and instead of replacing the x value in the list for the new value (pretend it's y), it shows the following:
  x
  y</p>
  
  <p>The expected result would be:
  y</p>
  
  <p>I mean, i don't want values to be on top of eachother, just one at a time.</p>