ASP.NET动态生成控件

     前两天写了个模块，需要从数据库读出数据在根据数据动态生成WEB控件。因为以前没写过，所以遇到一个问题，调了很久才调通。原来动态生成控件每次刷新页面都得在Page_Load()方法里面重现（生成控件代码不能写在if(!PageIsPost){}里面），不然在其他地方拿不到生成控件的值。用FindControls方法取控件值会抛出控异常。

下面是Page_Load（）事件里面的部分代码：

 SqlConnection conn = new SqlConnection(txtSqlConn.Text);
                   SqlDataAdapter da = new SqlDataAdapter("select top 1 * from (" + txtSelect.Text + ") t1", conn);
                   try
                   {
                       conn.Open();
                       DataSet ds = new DataSet();
                       da.Fill(ds, "InfoTable");
                       Table tb = new Table();//创建一个表格
                       
                       tb.BorderWidth = Unit.Parse("0");
                       tb.Width = Unit.Parse("100%");
                       for (int i = 0; ds.Tables[0].Columns.Count > i; i++)
                       {
                           if (ds.Tables["InfoTable"].Columns[i].DataType.ToString() == "System.Int32")
                           {
                               TableRow tr = new TableRow();//创建一行
                               TableCell cell1 = new TableCell();//创建单元格,也就是第一列
                               Label lbl = new Label();
                               lbl.ID = "lblName" + (int.Parse(ViewState["columns"].ToString()) + 1);
                               lbl.Text = ds.Tables["InfoTable"].Columns[i].ColumnName;
                               cell1.Controls.Add(lbl);
                               tr.Cells.Add(cell1);//添加到行中
                               TableCell cell2 = new TableCell();//创建第二列
                               DropDownList List = new DropDownList();
                               List.ID = "List" + (int.Parse(ViewState["columns"].ToString()) + 1);
                               //List.AutoPostBack = true;
                               List.Items.Add("无    ");
                               List.Items.Add("求和");
                               List.Items.Add("最大值");
                               List.Items.Add("最小值");
                               List.Items.Add("平均数");
                               cell2.Controls.Add(List);
                               tr.Cells.Add(cell2);
                               tb.Rows.Add(tr);//添加到表格中
                               ViewState["columns"] = int.Parse(ViewState["columns"].ToString()) + 1;
                           }
                       }
                       PlaceHolder1.Controls.Add(tb);
                   }
                   catch (Exception ex)
                   {
                       ErrorInfo.Text = ex.ToString();
                   }
                   finally
                   {
                       conn.Close();
                   }

下面是按钮事件里取控件值：

 string info = "";
                    for (int i = 0; i < int.Parse(ViewState["columns"].ToString()); i++)
                    {
                        Label lbl = (Label)PlaceHolder1.FindControl("lblName" + (i + 1));
                        DropDownList list = (DropDownList)PlaceHolder1.FindControl("List" + (i + 1));
                        info += lbl.Text + "," + list.SelectedItem.Text + ";";
                    }