若要将属性添加到ASP.NET标记中的属性列表并确保其在回发过程中保持不变，可以使用ViewState存储属性值。下面是如何实现此目的的示例：
1.将OnDataBound属性添加到标记中的GridView：

<asp:GridView ID="YourGridViewID" runat="server" OnRowDataBound="FormGV_RowDataBound" OnDataBound="GridView_DataBound">
    <!-- Your GridView markup here -->
</asp:GridView>

1.在代码隐藏中，修改RowDataBound事件处理程序以将属性值存储在ViewState：

protected void FormGV_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        DropDownList AnswerDD = (DropDownList)e.Row.FindControl("YourDropDownListID"); // Replace with your actual DropDownList ID
        ListItem listItem = new ListItem("YourText", "YourValue");

        // Populate the DropDownList dynamically
        listItem.Attributes.Add("DateOfService", form.sfc.DateOfThisService.ToString());
        AnswerDD.Items.Add(listItem);

        // Store the attribute value in ViewState
        ViewState[AnswerDD.ClientID + "_DateOfService"] = form.sfc.DateOfThisService.ToString();
    }
}

中
1.实现OnDataBound事件处理程序以在回发时设置回属性值：

protected void GridView_DataBound(object sender, EventArgs e)
{
    foreach (GridViewRow row in YourGridViewID.Rows)
    {
        if (row.RowType == DataControlRowType.DataRow)
        {
            DropDownList AnswerDD = (DropDownList)row.FindControl("YourDropDownListID"); // Replace with your actual DropDownList ID

            // Retrieve the attribute value from ViewState and set it back
            if (ViewState[AnswerDD.ClientID + "_DateOfService"] != null)
            {
                string dateOfService = ViewState[AnswerDD.ClientID + "_DateOfService"].ToString();
                ListItem listItem = AnswerDD.Items.FindByValue("YourValue"); // Replace with your actual value
                if (listItem != null)
                {
                    listItem.Attributes["DateOfService"] = dateOfService;
                }
            }
        }
    }
}