ASP.Net中的C＃列表框

Question

How can i check whether item S (already in listbox1) exists in listbox2? I used following code but it shows :

The best overloaded method match for 'System.Web.UI.WebControls.ListItemCollection.Contains(System.Web.UI.WebControl s.ListItem)' has some invalid arguments

Here is my code :

foreach (ListItem i in ListBox1.Items)
{
    string s = i.Text;
    Response.Write(s);

    if ((ListBox2.Items.Contains(s) == true))
    {
        Response.Write("Already");
    }
    else
    {
        Response.Write(ListBox1.SelectedItem.ToString());
        l1.Text += "<li>" + i.Text;
        ListBox2.Items.Add(i.Text);
    }
}

Answer 1

Item is a listitem and not a string and thus you should pass the listitem instead like

foreach (ListItem i in ListBox1.Items)
{
    string s = i.Text;
    Response.Write(s);

    if ((ListBox2.Items.Contains(i) == true))