DEV控件有关问题

DEV控件问题
ASPxComboBox无法下拉，点击不出现下拉框，没有任何反应
控件是运行是代码插入的

C# code

 ASPxComboBox cbxRelation = new ASPxComboBox() { Width = 50, HorizontalAlign = HorizontalAlign.Center, CssClass = "dynLabel" };                            var lstOp = new List<Tuple<string, string>>();                            lstOp.Add(new Tuple<string, string>(">", ">"));                            lstOp.Add(new Tuple<string, string>("<", "<"));                            lstOp.Add(new Tuple<string, string>(">=", ">="));                            lstOp.Add(new Tuple<string, string>("<=", "<="));                            cell.Controls.Add(cbxRelation);                            cbxRelation.DataSource = lstOp;                            cbxRelation.TextField = "item2";                            cbxRelation.ValueField = "item1";                            cbxRelation.Enabled = true;                            cbxRelation.DataBind();                            //cbxRelation.SelectedIndex = 3;                            ASPxTextBox drpNumber = new ASPxTextBox();                            cell.Controls.Add(drpNumber);