objectDataSource的参数如果把gridview的columns设成readonly就取不到为什么

参考代码
    <asp:GridView ID="DataView" runat="server" AutoGenerateColumns =false AutoGenerateEditButton=true EditRowStyle-BackColor=Blue SelectedRowStyle-BackColor=Beige  DataSourceID =ObjectDataSource1>
                <AlternatingRowStyle BackColor=Coral />
                <RowStyle BackColor = green   />
                <EditRowStyle BackColor=AliceBlue />
                <Columns >
                <asp:BoundField HeaderText = "LoginId" DataField = "LOGIN_ID" Readonly=true />
                <asp:BoundField HeaderText ="Privilege" DataField = "AUTH" InsertVisible =true  />
                </Columns>
                </asp:GridView>
                <asp:ObjectDataSource ID="ObjectDataSource1" runat="server" SelectMethod="selectview" TypeName="PageView" UpdateMethod="updateview">
                    <UpdateParameters>
                        <asp:Parameter Name = "LOGIN_ID" Type =string />
                        <asp:Parameter Name = "AUTH" Type = string />
                    </UpdateParameters>
                </asp:ObjectDataSource>更新的时候取不到loginid的值，去掉readonly=true就好了。