ListBox多选后台取值

前台：

<asp:ListBox ID="lbDepartment" runat="server"  SelectionMode="Multiple" Height="54px">
</asp:ListBox>

后台：

for (int i = 0; i < this.lbDepartment.Items.Count; i++)
   {
      if (this.lbDepartment.Items[i].Selected)
         {
             str += lbDepartment.Items[i].Text + ",";
          }
   }