事件“ItemUpdating”中的 OldValues 集合DetailsView 的始终为空

Question

我正在使用DetailsView，但更新时，我无法获取OldValues，因为ItemUpdating 事件的DetailsViewUpdateEventArgs.OldValues 始终为空。 NewValues 的值正常。

注意：我没有在应用程序中使用数据源组件（SqlDataSource、ObjectDataSource、EntityDataSource 等）。在这种情况下我应该手动做一些事情吗？

任何想法都将受到欢迎！

谢谢！

补充信息：

我正在使用 ASP.NET 4.0 (WebForms)

我认为下面相关的代码片段：

<asp:DetailsView ID="customerDetails" runat="server" AutoGenerateRows="False" EmptyDataText="No data..." 
    meta:resourcekey="customerDetails" 
    onitemdeleting="customerDetails_ItemDeleting" 
    oniteminserting="customerDetails_ItemInserting" 
    onitemupdating="customerDetails_ItemUpdating" 
    onmodechanging="customerDetails_ModeChanging" 
    CssClass="customerDetails" DataKeyNames="CustomerID">
    <FooterTemplate>
        <asp:LinkButton ID="lnkNew" Text="New" ToolTip="New Customer" CommandName="New" meta:resourcekey="lnkNew" runat="server" />
    </FooterTemplate>
    <EmptyDataTemplate>
        <p><asp:Label ID="lblNoDataHasBeenFound" Text="No data has been found." meta:resourcekey="lblNoDataHasBeenFound" runat="server" /></p>
        <asp:LinkButton ID="lnkNew" Text="New" ToolTip="New Customer" CommandName="New" meta:resourcekey="lnkNew" runat="server" />
    </EmptyDataTemplate>
    <Fields>
        <%--CustomerID--%>
        <asp:TemplateField HeaderStyle-CssClass="detailsHeader" ItemStyle-CssClass="detailsField">
            <HeaderTemplate>
                <asp:Label ID="ltrCustomerIdLabel" meta:resourcekey="ltrCustomerId" Text="CustomerID:" runat="server" />
            </HeaderTemplate>
            <ItemTemplate>
                <asp:Label ID="lblCustomerId" Text='<%# Eval("CustomerID") %>' runat="server"  />
            </ItemTemplate>
            <EditItemTemplate>
                <asp:Label ID="lblCustomerId" Text='<%# Eval("CustomerID") %>' runat="server"  />
            </EditItemTemplate>
            <InsertItemTemplate>
                <asp:TextBox ID="txtCustomerId" Text='<%# Bind("CustomerID") %>' MaxLength="5" width="50px" runat="server" />
                <cc1:DataAnnotationsValidator ID="CustomerIdValidator" Type="String" runat="server" ControlToValidate="txtCustomerId" PropertyName="CustomerID" Text="*" SourceType="DataLayerPOCO.Customer, DataLayerPOCO" CssError="validationError" Display="None"/>
            </InsertItemTemplate>
            <HeaderStyle HorizontalAlign="Right" />
            <ItemStyle HorizontalAlign="Left" />
        </asp:TemplateField>

        <%--CompanyName--%>
        <asp:TemplateField HeaderStyle-CssClass="detailsHeader" ItemStyle-CssClass="detailsField">
            <HeaderTemplate>
                <asp:Literal ID="ltrCompanyNameLabel" meta:resourcekey="ltrCompanyName" Text="Company Name:" runat="server" />
            </HeaderTemplate>
            <ItemTemplate>
                <asp:Literal ID="ltrCompanyName" Text='<%# Eval("CompanyName") %>' runat="server"/>
            </ItemTemplate>
            <EditItemTemplate>
                <asp:TextBox ID="txtCompanyName" Text='<%# Bind("CompanyName") %>' MaxLength="40" Width="310px"
                    runat="server" />
                <cc1:DataAnnotationsValidator ID="CompanyNameValidator" Type="String" runat="server" ControlToValidate="txtCompanyName" PropertyName="CompanyName" Text="*" SourceType="DataLayerPOCO.Customer, DataLayerPOCO" CssError="validationError" Display="None"/>
            </EditItemTemplate>
            <InsertItemTemplate>
                <asp:TextBox ID="txtCompanyName" Text='<%# Bind("CompanyName") %>' MaxLength="40" Width="310px"
                    runat="server" />
                <cc1:DataAnnotationsValidator ID="CompanyNameValidator" Type="String" runat="server" ControlToValidate="txtCompanyName" PropertyName="CompanyName" Text="*" SourceType="DataLayerPOCO.Customer, DataLayerPOCO" CssError="validationError" Display="None"/>
            </InsertItemTemplate>
            <HeaderStyle HorizontalAlign="Right" />

        </asp:TemplateField>
        ...
        ...
        other fields goes here
        ...
        ...
        <%--Edit/Insert--%>
        <asp:TemplateField HeaderStyle-CssClass="detailsHeader" ItemStyle-CssClass="detailsField">
            <ItemTemplate>
                <asp:ImageButton ID="imgEdit" ImageUrl="~/img/pencil.png" meta:resourcekey="imgEdit" AlternateText="Edit" ToolTip="Edit Customer" CommandName="Edit" runat="server" CausesValidation="false"/>
                <asp:ImageButton ID="imgDelete" ImageUrl="~/img/delete.png" meta:resourcekey="imgDelete" AlternateText="Delete" ToolTip="Delete Customer" CommandName="Delete" OnClientClick="return confirmDelete();" runat="server" CausesValidation="false"/>
            </ItemTemplate>
            <EditItemTemplate>
                <asp:ImageButton ID="imgUpdate" ImageUrl="~/img/accept.png" meta:resourcekey="imgUpdate" AlternateText="Update" ToolTip="Update Customer" CommandName="Update" runat="server" />
                <asp:ImageButton ID="imgCancel" ImageUrl="~/img/cancel.png" meta:resourcekey="imgCancel" AlternateText="Cancel" ToolTip="Cancel Edit" CommandName="Cancel" runat="server" CausesValidation="false"/>
            </EditItemTemplate>
            <InsertItemTemplate>
                <asp:ImageButton ID="imgSave" ImageUrl="~/img/disk.png" meta:resourcekey="imgSave" AlternateText="Save" ToolTip="Save Customer Data" CommandName="Insert" runat="server" CausesValidation="true"/>
                <asp:ImageButton ID="imgCancelInsert" ImageUrl="~/img/cancel.png" meta:resourcekey="imgCancelInsert" AlternateText="Cancel" ToolTip="Cancel Insert" CommandName="Cancel" runat="server" CausesValidation="false"/>
            </InsertItemTemplate>
        </asp:TemplateField>
    <Fields>
</asp:DetailsView>

事件 ItemUpdating 如下所示：

    protected void customerDetails_ItemUpdating(object sender, DetailsViewUpdateEventArgs e)
    {
        repository = repository ?? new NorthwindRepositoryEF();

        string id = e.Keys["CustomerID"] as string;

        DataLayerPOCO.Customer customer = repository.GetCustomer(id);

        string companyName = (string)e.NewValues["CompanyName"];
        string contactName = (string)e.NewValues["ContactName"];
        string contactTitle = (string)e.NewValues["ContactTitle"];
        string address = (string)e.NewValues["Address"];
        string city = (string)e.NewValues["City"];
        string region = (string)e.NewValues["Region"];
        string postalCode = (string)e.NewValues["PostalCode"];
        string country = (string)e.NewValues["Country"];
        string phone = (string)e.NewValues["Phone"];
        string fax = (string)e.NewValues["Fax"];

        // Update Customer with the new data
        customer.CompanyName = companyName;
        customer.ContactName = contactName;
        customer.ContactTitle = contactTitle;
        customer.Address = address;
        customer.City = city;
        customer.Region = region;
        customer.PostalCode = postalCode;
        customer.Country = country;
        customer.Phone = phone;
        customer.Fax = fax;

        repository.UpdateCustomer(customer);
        repository.Save();
        //---
        customerDetails.ChangeMode(DetailsViewMode.ReadOnly);
        BindCustomerDetails();
        BindCustomersList();

    }

问题是，如果我想处理旧值，我可以t：

这个，计算结果为 0： int oldValuesCount = e.OldValues.Count;

即使我将该值更改为新值，其计算结果仍为 null： string companyNameOld = e.OldValues["CompanyName"] as string;

Answer 1

看来只有当您有声明性限制的数据源时才会填充旧值。

在这种情况下，您有两种解决方法：

1. 以编程方式在 ViewState 中保存您可能需要的任何旧值，并在需要时检索它。这样可以节省一次数据库访问。

2. 更好的选择是使用您在 OnItemUpdating 中定义的客户变量，因为它从数据库查询信息并包含所有旧值。

希望有帮助。