C# ASP.Net：ListView 的 ItemTemplate 中的条件逻辑
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ASP.Net: Conditional Logic in a ListView's ItemTemplate
提问by Andreas Grech
I want to show certain parts of an ItemTemplatebased according to whether a bound field is null. Take for example the following code:
我想ItemTemplate根据绑定字段是否为空来显示基于的某些部分。以下面的代码为例：
(Code such as LayoutTemplate have been removed for brevity)
（为简洁起见，已删除诸如 LayoutTemplate 之类的代码）
<asp:ListView ID="MusicList" runat="server">
<ItemTemplate>
<tr>
<%
if (Eval("DownloadLink") != null)
{
%>
<td>
<a href="<%#Eval("DownloadLink") %>">Link</a>
</td>
<%
} %>
</tr>
</ItemTemplate>
</asp:ListView>
The above gives the following run-time error:
以上给出了以下运行时错误：
Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control.
Eval()、XPath() 和 Bind() 等数据绑定方法只能在数据绑定控件的上下文中使用。
So how can put some conditional logic (like the above) in an ItemTemplate?
那么如何将一些条件逻辑（如上述）放入ItemTemplate?
采纳答案by Neil Fenwick
What about binding the "Visible" property of a control to your condition? Something like:
将控件的“可见”属性绑定到您的条件怎么样？就像是：
<asp:ListView ID="MusicList" runat="server">
<ItemTemplate>
<tr runat="server" Visible='<%# Eval("DownloadLink") != null %>'>
<td>
<a href='<%#Eval("DownloadLink") %>'>Link</a>
</td>
</tr>
</ItemTemplate>
</asp:ListView>
回答by MikeD
I'm not recommending this as a good approach but you can work around this issue by capturing the current item in the OnItemDataBound event, storing it in a public property or field and then using that in your conditional logic.
我不建议将此作为一种好方法，但您可以通过在 OnItemDataBound 事件中捕获当前项目，将其存储在公共属性或字段中，然后在您的条件逻辑中使用它来解决此问题。
For example:
例如：
<asp:ListView ID="MusicList" OnItemDataBound="Item_DataBound" runat="server">
<ItemTemplate>
<tr>
<%
if (CurrentItem.DownloadLink != null)
{
%>
<td>
<a href="<%#Eval("DownloadLink") %>">Link</a>
</td>
<%
} %>
</tr>
</ItemTemplate>
</asp:ListView>
And on the server side add the following code to your code behind file:
在服务器端，将以下代码添加到您的代码隐藏文件中：
public MusicItem CurrentItem { get; private set;}
protected void Item_DataBound(object sender, RepeaterItemEventArgs e)
{
CurrentItem = (MusicItem) e.Item.DataItem;
}
Note that this trick will not work in an UpdatePanelcontrol.
请注意，此技巧在UpdatePanel控件中不起作用。
回答by Zesxter
If you have 2 different structure that are to be rendered according to a condition then use panels
如果您有 2 个不同的结构要根据条件渲染，则使用面板
<asp:ListView ID="MusicList" runat="server">
<ItemTemplate>
<tr>
<asp:Panel ID="DownloadNull" runat="server" Visible="<%# Eval("DownloadLink") == null %>" >
<td> Album Description BlaBlaBla <img src="../images/test.gif"> </td>
</asp:Panel>
<asp:Panel ID="DownloadNotNull" runat="server" Visible="<%# Eval("DownloadLink") != null %>" >
<td> Album Description BlaBlaBla <img src="../images/test.gif">
<a href='<%# Eval("DownloadLink")' >Download</a>
.....
</td>
</asp:Panel>
</tr>
</ItemTemplate>
</asp:ListView>
回答by Shamozzle
To resolve "The server tag is not well formed." for the answers involving visibility, remove quotes from the Visible= parameter.
解决“服务器标签格式不正确”。对于涉及可见性的答案，请从 Visible= 参数中删除引号。
So it will become:
所以它会变成：
<tr runat="server" Visible=<%# Eval("DownloadLink") != null ? true : false %>>
