如何在 EditItemTemplate 中自动回发？

Question

我在 FormView EditItemTemplate 中有几个 DropDownList。其中一个是经纪人列表，另一个是经纪人账户列表。当经纪商 DropDownList 更改时，我希望账户 DropDownList 中填充该经纪商的账户列表。

页面如下所示：

<asp:FormView
    ID="fvwEditTrade"
    DataSourceID="srcTrade" 
    runat="server" 
    DataKeyNames="tradeId" 
    DefaultMode="Edit" 
    CssClass="formView"
    OnItemUpdated="fvwEditTrade_Updated" 
    OnItemCommand="fvwEditTrade_Command" 
    OnItemUpdating="fvwEditTrade_Updating"            
    >
<EditItemTemplate>
    <asp:Label ID="lblTradeId" Text="TradeId: " runat="server" CssClass="label" /><%# Eval("tradeId") %>
    <br />

    <asp:Label ID="lblBroker" Text="Broker" runat="server" CssClass="label" />
    <asp:DropDownList 
    ID="ddlBrokers" 
    runat="server" 
    CssClass="dropdownlist" 
    DataSourceID="srcBrokers" 
    DataTextField="broker" 
    DataValueField="brokerId" 
    SelectedValue='<%# Bind("brokerId") %>'  
    AutoPostBack="true"             
     />
    <br />  

    <asp:Label ID="lblAccount" Text="Account" AssociatedControlID="ddlAccounts" runat="server" CssClass="label" />
    <asp:DropDownList 
    ID="ddlAccounts" 
    runat="server" 
    CssClass="dropdownlist" 
    DataSourceID="srcAccounts" 
    DataTextField="description" 
    DataValueField="accountId" 
    SelectedValue='<%# Bind("accountId") %>' 
     />
    <br />

然后，

   <asp:Button
    id="lnkUpdate"
    Text="Update"
    CommandName="Update" CssClass="button"
    Runat="server" />

    <asp:Button
    id="lnkCancel"
    Text="Cancel"
    CommandName="Cancel" CssClass="button"
    Runat="server" />

</EditItemTemplate>
</asp:FormView>            


<CustomControls:CustomObjectDataSource
    id="srcTrade" 
    TypeName="DatabaseComponent.DBUtil" 
    SelectMethod="GetTrade"
    UpdateMethod="UpdateTrade"
    runat="server">
    <SelectParameters>
    <asp:QueryStringParameter Name="tradeId" QueryStringField="tradeId" />               
    </SelectParameters>
    <UpdateParameters>                
    <asp:ControlParameter Name="tradeId" ControlId="fvwEditTrade" PropertyName="SelectedValue" />
    <asp:ControlParameter Name="accountId" ControlId="fvwEditTrade$ddlAccounts" PropertyName="SelectedValue" />
    <asp:ControlParameter Name="symbol" ControlId="fvwEditTrade$ddlSymbols" PropertyName="SelectedValue" />
    <asp:ControlParameter Name="riskProfileId" ControlId="fvwEditTrade$ddlRiskProfiles" PropertyName="SelectedValue" />
    <asp:ControlParameter Name="pctAccountRisked" ControlId="fvwEditTrade$txtPctAccountRisked" PropertyName="Text" />
    <asp:ControlParameter Name="tradeSetupId" ControlId="fvwEditTrade$ddlSetups" PropertyName="SelectedValue" />
    <asp:ControlParameter Name="amountPerUnit" ControlId="fvwEditTrade$txtamountPerUnit" PropertyName="Text" />
    <asp:ControlParameter Name="initialStopPrice" ControlId="fvwEditTrade$txtInitialStopPrice" PropertyName="Text" />
    <asp:ControlParameter Name="tfCode" ControlId="fvwEditTrade$ddlTimeFrames" PropertyName="SelectedValue" />
    <asp:ControlParameter Name="MAEPips" ControlId="fvwEditTrade$txtMAEPips" PropertyName="Text" />
    <asp:ControlParameter Name="MFEPips" ControlId="fvwEditTrade$txtMFEPips" PropertyName="Text" />
    <asp:ControlParameter Name="tradeGrade" ControlId="fvwEditTrade$ddlTradeGrades" PropertyName="SelectedValue" />
    <asp:ControlParameter Name="executionGrade" ControlId="fvwEditTrade$ddlExecutionGrades" PropertyName="SelectedValue" />
    <asp:ControlParameter Name="comment" ControlId="fvwEditTrade$txtComments" PropertyName="Text" />
    </UpdateParameters>
</CustomControls:CustomObjectDataSource>

<CustomControls:CustomObjectDataSource
    id="srcBrokers" 
    TypeName="DatabaseComponent.DBUtil" 
    SelectMethod="GetBrokers" 
    runat="server">
</CustomControls:CustomObjectDataSource>

<CustomControls:CustomObjectDataSource
    id="srcAccounts" 
    TypeName="DatabaseComponent.DBUtil" 
    SelectMethod="GetBrokerAccounts" 
    runat="server">
    <SelectParameters>
    <asp:ControlParameter Name="brokerId" ControlId="fvwEditTrade$ddlBrokers" PropertyName="SelectedValue" />
    </SelectParameters>
</CustomControls:CustomObjectDataSource>        

当页面加载时，我收到此错误：

Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control.

如果我将 CustomObjectDataSources srcBrokers 和 srcAccounts 移动到 EditItemTemplate“内部”，则页面加载正常，但是，当我在 ddlBrokers 中选择代理时，我得到相同的结果再次错误：

Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control.

关于如何解决这个问题有什么想法吗？数据源应该位于 EditItemTemplate 外部还是内部？

Answer 1

从 ddlAccounts 中删除绑定表达式 SelectedValue='<%# Bind("accountId") %>'。这是造成问题的原因。您需要从代码后面处理这个问题。

当项目尝试更新时，您必须在 FormView ItemUpdating Event 中传递此下拉选定值

Answer 2

为 FormView 的 ItemUpdated 发生时添加一个标志。
在 FormView 的 PreRender 中检查 if (IsPostBack && !_fvWasUpdated) {formView1.DataBind();}

这将修复它。问题是 FormView 不会在回发时执行 DataBinding，如果回发不是来自 formview 本身，它将丢失其数据上下文。

Answer 3

您可以尝试使用 Eval() 而不是 Bind()

Answer 4

SelectedValue='<%# xx(DataBinder.Eval(Container.DataItem,"fieldname")) %>' 

让 xx 成为一个像这样的函数：

Function xx(ByVal a As String) As String
    Return a
End Function