将CheckBoxList选中项转成字符串

              string str1;
                str1 = null;
                for (int i = 0; i < CBL_da.Items.Count; i++)
                {
                    if (CBL_da.Items[i].Selected)
                    {
                        str1 = str1 + CBL_da.Items[i].Text + ",";
                    }
                }

//CBL_da是CheckBoxList控件的ID