ASP.NET listbox selectedValue in PageLoad

Question

I have a problem with listbox. I would like to fill it with data and select Value (listbox.SelctedValue), using postback, after textbox is filled and Page.Validate() is fired. I try to use it in Page_Load. Everything works fine until I dont mark another user. It goes back to the the first one. I know its because I mark the first one again and again it in Page_Load, but how can I mark user after postback in other place? I cant use any buttons.

To be more clear, I have one text box, which causes postback after user put text there. After that I would like to check if Page.Isvalid and is yes, add that user to listbox (which also causes postbacks) and mark him. Without any buttons. How can I do it only once, using autopostback, not every PageLoad ?

Answer 1

Try this

protected void Page_Load(object sender, EventArgs e)
{
    if (Page.IsPostBack)
    {
        if (Page.IsValid)
        {
            //Mylistbox.SelctedValue = set Your Selected Value
        }
    }
}