“DdlCategoryChildren”有一个无效 SelectedValue，因为它不在项目列表中。

        DataTable dataTable = new DataTable("CategoryChildren");
        DataColumn newCoulumn;
        newCoulumn = dataTable.Columns.Add("CategoryId", Type.GetType("System.String"));
        newCoulumn = dataTable.Columns.Add("CategoryName", Type.GetType("System.String"));

        string selChildren = "select * from Category where ParentId like '%" + ddlParentName.SelectedValue.ToString() + "%'";
        DataTable dtChildren = simple.GetResultToDataTable(selChildren);
        DataRow newRow;
        if (dtChildren.Rows.Count > 0)
        {
            for (int j = 0; j < dtChildren.Rows.Count; j++)
            {
                //if (dtChildren.Rows[j]["ParentId"].ToString() != "")
                //{
                newRow = dataTable.NewRow();
                string aaaaaa = dtChildren.Rows[j]["CategoryId"].ToString();
                newRow["CategoryId"] = dtChildren.Rows[j]["CategoryId"].ToString();
                newRow["CategoryName"] = dtChildren.Rows[j]["CategoryName"].ToString();
                dataTable.Rows.Add(newRow);

            }
        }
        if (dtChildren.Rows.Count > 0)
        {
            DdlCategoryChildren.Items.Clear();
            DdlCategoryChildren.DataSource = dataTable;
            DdlCategoryChildren.DataTextField = dataTable.Columns["CategoryName"].ToString();
            DdlCategoryChildren.DataValueField = dataTable.Columns["CategoryId"].ToString();
            DdlCategoryChildren.DataBind();
        }
        string ddl = "无";
        ListItem li = new ListItem(ddl, "");
        this.DdlCategoryChildren.Items.Insert(0, li);
        this.DdlCategoryChildren.SelectedValue = "";


我用上面语句绑定dropdownList,出现下面错无,郁闷!~

异常详细信息: System.ArgumentOutOfRangeException: “DdlCategoryChildren”有一个无效 SelectedValue，因为它不在项目列表中。
参数名: value


我在绑定前 清空 dropDownList的items了
怎么还会有selectedValue的列表那
百思不得其解啊!~