调试易

SqlConnection cn = new SqlConnection("Data Source = localhost;User ID = sa;Password = pp;DATABASE = db");
            cn.Open();
            SqlCommand cmd = new SqlCommand("Select wo_id,wo_state from Working",cn);
            DataTable tbl = new DataTable();
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            da.Fill(tbl);
            for (int i = 0; i < tbl.Rows.Count; i++)
            {
                ListViewItem lvi = new ListViewItem();
                switch (tbl.Rows[i]["wo_state"].ToString())
                {
                    case "完成":
                        lvi.ForeColor = Color.Red;
                        break;
                    case "开始":
                        lvi.ForeColor = Color.Green;
                        break;
                    case "待工":
                        lvi.ForeColor = Color.Blue;
                        break;
                    default:
                        break;
                }
                lvi.Text = tbl.Rows[i]["wo_id"].ToString();
                ltv1.Items.Add(lvi);
            }
这样写应该没错吧，就是不行，列出来的几个Item全是黑色的字。
但是这么写又可以：
for (int i = 0; i < 10; i++)
            {
                ListViewItem lvi = new ListViewItem();
                switch (i % 3)
                {
                    case 0:
                        lvi.ForeColor = Color.Red;
                        break;
                    case 1:
                        lvi.ForeColor = Color.Blue;
                        break;
                    case 2:
                        lvi.ForeColor = Color.Green;
                        break;
                    default:
                        break;
                }
                lvi.Text = i.ToString();
                ListView1.Items.Add(lvi);
            }
LitsView控件和TreeView控件都是这样，这是郁闷！
我快疯了，谁能帮帮我！？告诉我到底错在哪里？