How to know which items are selected in a multi-select ListBox

I may have asked a simple question..
but i m just not able to figure it out.

Generally we provide the users with two listbox where the first one is a list of available and the other selected ones.

I found a solution in JavaScript but i would like to have it thru ASP.Net Server Side coding only.

pls suggest

Basically, you go "for each" loop through list items and each item should have property Selected

kind of like this

VB Code:

Dim item As ListItem
 
For each item in ListBox1.Items
   If(item.Selected) Then
      'do something with the selected item
   End If
Next