ASP:ListBox Get Selected Items - One Liner?

Using LINQ:

string values = String.Join(", ", lbAppGroup.Items.Cast<ListItem>()
                                                  .Where(i => i.Selected)
                                                  .Select(i => i.Value));

I don't think there is anything built in but you could do something like this:

  <asp:ListBox runat="server" ID="listBox" SelectionMode="Multiple">
    <asp:ListItem Selected="True" Text="text1" Value="value1"></asp:ListItem>
    <asp:ListItem Selected="false" Text="text2" Value="value2"></asp:ListItem>
    <asp:ListItem Selected="True" Text="text3" Value="value3"></asp:ListItem>
    <asp:ListItem Selected="True" Text="text4" Value="value4"></asp:ListItem>
</asp:ListBox>

    IEnumerable<string> selectedValues = from item in listBox.Items.Cast<ListItem>()
                                             where item.Selected
                                             select item.Text;

        string s = string.Join(",", selectedValues);

var selectedQuery = listBox.Items.Cast<ListItem>().Where(item => item.Selected); 
string selectedItems =  String.Join(",", selectedQuery).TrimEnd();