C# 如何在gridview中获取dropdownlist中的值？

在gridview中有一个dropdownlist

<asp:TemplateField HeaderText="Quantity">
    <ItemTemplate>
        <asp:DropDownList ID="quantity" runat="server" DataValueField="ItemID" DataTextField="Quantity">
        </asp:DropDownList>
    </ItemTemplate>
</asp:TemplateField>

---

我会在

TemplateField

中添加一个

HiddenField

来保存CartID，我会在代码中使用CartID。我的标记应该如下所示：

<asp:TemplateField HeaderText="Quantity">
    <ItemTemplate>
        <asp:DropDownList ID="quantity" runat="server" DataValueField="ItemID" DataTextField="Quantity">
        </asp:DropDownList>
    </ItemTemplate>
</asp:TemplateField>

<asp:TemplateField HeaderText="Quantity">
    <ItemTemplate>  
        <asp:HiddenField ID="hdnId" runat="server" value='<%#Eval("CartID") %>'></asp:HiddenField>                            
        <asp:DropDownList ID="quantity" runat="server" DataValueField="ItemID" DataTextField="Quantity">
        </asp:DropDownList>
    </ItemTemplate>
</asp:TemplateField>

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        DropDownList quantity = e.Row.FindControl("quantity") as DropDownList;
        HiddenField hdnId = e.Row.FindControl("hdnId") as HiddenField;

        if (quantity != null && hdnId != null)
        {
            string queryString = String.Format("SELECT ItemID, Quantity FROM  CartItems  WHERE CartID= {0}", hdnId.Value);

            //MyConnectionString is your connection string in web.config
            using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["MyConnectionString"].ToString()))
            {
                SqlCommand command = new SqlCommand(queryString, connection);
                connection.Open();
                SqlDataReader reader = command.ExecuteReader();
                quantity.DataSource = reader;
                quantity.DataValueField = "ItemID";
                quantity.DataTextField = "Quantity";
                quantity.DataBind();               
            }
        }        

    }
}