转发器中的 if else 逻辑（aspx 页面）

Question

我的网站上有一个中继器，然后我需要执行以下代码：

<% if(Eval("TypeID") = 5) then %>
    <%# Html.BtnDigital(Eval("ID").ToString(),Eval("Title").ToString())%>
<% end if %>

基本上：如果数据绑定项的属性是 5，我需要做一些特别的事情。

我无法通过添加新属性来更改数据绑定项（很遗憾），而且我现在仅限于 VB.NET。

当我没有 if 语句时，按钮显示正常，但是当我有 if 语句时，我收到以下错误（抱歉丹麦语）：

System.InvalidOperationException: Databindingmetoder som Eval(), XPath() og Bind() kan kun bruges i forbindelse med et databundet kontrolelement.
   ved System.Web.UI.Page.GetDataItem()
   ved System.Web.UI.TemplateControl.Eval(String expression)
   ved ASP.controls_guidesection_ascx.__Render__control19(HtmlTextWriter __w, Control parameterContainer) i C:\Users\larsholdgaard\Documents\Work\SAXO.com\Saxo.Websites.Base\src\Saxo.Website.Base\Controls\GuideSection.ascx:linje 75
   ved System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   ved System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   ved System.Web.UI.Control.Render(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   ved System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   ved System.Web.UI.Control.Render(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   ved System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   ved System.Web.UI.Control.Render(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   ved System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   ved System.Web.UI.Control.Render(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   ved System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   ved System.Web.UI.Control.Render(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   ved System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   ved System.Web.UI.Control.Render(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   ved System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   ved System.Web.UI.Control.Render(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   ved ASP.views_masterpages_saxomasterpage_master.__Render__control1(HtmlTextWriter __w, Control parameterContainer) i C:\Users\larsholdgaard\Documents\Work\SAXO.com\Saxo.Websites.Base\src\Saxo.Website.Base\Views\Masterpages\SaxoMasterPage.Master:linje 74
   ved System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   ved System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   ved System.Web.UI.Control.Render(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   ved System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   ved System.Web.UI.Page.Render(HtmlTextWriter writer)
   ved System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   ved System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   ved System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

谢谢:)

Answer 1

解决这种情况的一个好方法是对中继器的ItemDataBound-事件作出反应。 在 CodeBehind 中检查条件要容易得多。

例如，如果您想根据项目的值更改 ItemTemplate 中控件的可见性，您可以添加以下代码（以下代码是一个示例；我假设有ItemTemplate 中 ID 为“txtValue”的文本框）：

Private Sub Repeater_OnItemDatabound(Object sender, RepeaterItemEventArgs e)
    If e.Item.ItemType = ListItemType.Item OrElse e.Item.ItemType = ListItemType.AlternatingItem Then
        Dim myItem = TryCast(e.Item.DataItem, MyDataItemClass)
        Dim txtBox = TryCast(e.Item.FindControl("txtValue"), TextBox)
        If (txtBox IsNot Nothing) Then
            txtBox.Visible = myItem.TypeId = 5
           txtBox.Text = myItem.SomeInterestingText
        End If
    End If
End Sub

Answer 2

您需要做的是检查 ItemDataBound 事件中的值。这些将在每个项目被绑定时触发。在这甚至做你的检查，如果你有匹配做你的改变。

见http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.repeater.itemdatabound(v=vs.110).aspx

msdn 页面中的示例还显示了如何区分页眉和页脚行以及备用行模板（如果您使用它们）。在创建每一行时触发偶数。