[已解决]除非包含的Panel可见，如何防止Eval()被调用? [英] [Solved] How to prevent Eval() from being called unless the containing Panel is Visible?

问题描述

我有一个页面，如果该图像存在于Web服务器的磁盘上，我们希望显示该图像；否则，我们希望显示产品功能描述文本.

我的方法是实现两个asp:Panel控件，一个用于保存包含asp:ListView的<div>，该asp:ListView调用DB以显示产品功能文本.另一个asp:Panel以显示包含图像的<img>的<div>.

但是，我也想避免调用Eval()函数以调用DB来获取功能部件文本，除非显示了包含asp:Panel的功能部件文本.

我对以下代码有误吗?

I have a page where we want to either display an image of a product if the image exists on the disk of the web server, or if not, we want product features description text displayed.

My approach was to implement two asp:Panel controls, one to hold the <div> containing the asp:ListView that calls the DB to display the product feature text; and another asp:Panel to display the <div> that contains the <img> for the image.

I want to also, though, avoid calling the Eval() function to call into the DB to get the feature text unless its containing asp:Panel is displayed.

Am I doing something wrong with the following code?

<asp:Panel runat="server" ID="pnlFeaturesText" Visible="false" CssClass="FeaturesList">
                    <div id="divFeaturesText">
                        <asp:ListView runat="server" ID="lstFeatures">
                            <layouttemplate>
                                <ul>
                                    <li  runat="server" id="itemPlaceholder" />
                                </ul>
                            </layouttemplate>
                            <itemtemplate>
                                <ul><li style="margin-removed 15px;">
                                    <asp:Label runat="server" Text='<%# if (pnlFeaturesText.Visible) { Eval("Feature1") } %>' Style="font-weight: 700;" Font-Names="Verdana" /><br />
                                    <asp:Label runat="server" Text='<%# if (pnlFeaturesText.Visible) { Eval("Benefit") } %>' Font-Names="Verdana" /></li></ul>
                            </itemtemplate>
                        
                    </div>

我特别在谈论台词

I am specifically talking about the lines

<asp:Label runat="server" Text='<%# if (pnlFeaturesText.Visible) { Eval("Feature1") } %>' Style="font-weight: 700;" Font-Names="Verdana" />

由于某种原因，我不能在Text属性中使用if语句；该页面返回异常无效的表达式:如果".

有什么解决方法?在我的代码中手动设置文本?它的语法是什么?

谢谢！

Brian

I can''t use an if statement in the Text property for some reason; the page returns the exception "Invalid expression: if".

What would be a workaround? Set the text by hand, in my code? What''s the syntax for that?

Thanks!

Brian

推荐答案

在您的代码后写一个方法，在其中放置if，然后从标记中调用您的方法.

Write a method in your code behind, put the if in there, and call your method from the markup.

public void ControlEval(string evalThis)
{
    if (pnlFeaturesText.Visible)
    {
        Eval(evalThis);
    }
}

然后您可以执行以下操作:

and then you can do this:

<asp:Label runat="server" Text='<%# ControlEval("Feature1"); %>' Style="font-weight: 700;" Font-Names="Verdana" /><br />
<asp:Label runat="server" Text='<%# ControlEval("Benefit"); %>' Font-Names="Verdana" /></li></ul>

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