I've been trying iterate through the selected items of a listbox in WPF, with the following code;

        try
        {
            for (int i = 0; i < mylistbox.SelectedItems.Count; i++)
            {
                ListItem li = (ListItem)mylistbox.SelectedItems[i];

                string listitemcontents_str = li.ToString();
            }
        }
        catch(Exception e)
        {
            // Error appears here
            string error = e.ToString();
        }

However I receive an invalid cast exception;

System.InvalidCastException: Unable to cast object of type 'mylist' to type 'System.Windows.Documents.ListItem'.

Is there a way around this?