asp.net-mvc ASP.NET MVC razor：HTML 中的条件属性
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ASP.NET MVC razor: conditional attribute in HTML
提问by Mahesh
Code below doesn't seems clean. Any suggestion to improve the code?
下面的代码似乎不干净。有什么建议可以改进代码吗？
<li @if(ViewData["pagename"].ToString()=="Business details"){ <text>class="active" </text> } >
<a @if(ViewData["pagename"].ToString()=="Business details"){ <text>style="color: white; background-color: #08C; border: 1px solid #08C;" </text> }
href="@Url.Action("BusinessDetails", "Business")">Business Details</a>
</li>
<li @if (ViewData["pagename"].ToString() == "Booking policies"){ <text>class="active"</text> }>
<a @if (ViewData["pagename"].ToString() == "Booking policies")
{ <text>style="color: white; background-color: #08C; border: 1px solid #08C;" </text> }
href="@Url.Action("BookingPolicies", "Business")">Booking policies</a>
</li>
回答by jcreamer898
MVC has conditional attributes built in...
MVC 具有内置的条件属性...
<div @{if (myClass != null) { <text>class="@myClass"</text> } }>Content</div>
<div class="@myClass">Content</div>
If @myClass is null, it just won't use the attribute at all...
如果@myClass 为空，则它根本不会使用该属性...
I know that may not quite solve your current issue, but it is noteworthy!
我知道这可能不能完全解决您当前的问题，但值得注意的是！
http://weblogs.asp.net/jgalloway/archive/2012/02/16/asp-net-4-beta-released.aspx
http://weblogs.asp.net/jgalloway/archive/2012/02/16/asp-net-4-beta-released.aspx
回答by SLaks
<li class="@(ViewBag.pagename == "Business details" ? "active" : null)">
You should replace the inline style="..."with a separate classname and use the same syntax there.
您应该用style="..."单独的类名替换内联并在那里使用相同的语法。
However, it would be cleaner to make a separate HTML helper extension method that takes a page and action name and generates the HTML generically.
但是，制作一个单独的 HTML 帮助程序扩展方法会更清晰，该方法接受页面和操作名称并生成一般的 HTML。
回答by defrost
I use a small helper method that will conditionally add an attribute if the value is non-empty, and, if defined, when a Boolean function expression evaluates to true:
我使用一个小的辅助方法，如果值不为空，并且如果定义，当布尔函数表达式计算为时，它将有条件地添加一个属性true：
public static MvcHtmlString Attr(this HtmlHelper helper, string name, string value, Func<bool> condition = null)
{
if (string.IsNullOrEmpty(name) || string.IsNullOrEmpty(value))
{
return MvcHtmlString.Empty;
}
var render = condition != null ? condition() : true;
return render ?
new MvcHtmlString(string.Format("{0}=\"{1}\"", name, HttpUtility.HtmlAttributeEncode(value))) :
MvcHtmlString.Empty;
}
Once defined, I can use this method in my Razor views:
定义后，我可以在 Razor 视图中使用此方法：
<li @(Html.Attr("class", "new", () => example.isNew))>
...
</li>
The above code will render <li class="new">...</li>if example.isNew == true, if not will omit the entire classattribute.
上面的代码将呈现<li class="new">...</li>if example.isNew == true， if not 将省略整个class属性。
回答by David Slavík
In MVC4
在MVC4中
<!DOCTYPE html>
<html>
<head>
</head>
<body>
@{
string css = "myDiv";
}
<div class='@css'></div>
</body>
</html>
or
或者
<!DOCTYPE html>
<html>
<head>
</head>
<body>
@{
string css = "class=myDiv";
}
<div @css></div>
</body>
</html>
More are here: http://evolpin.wordpress.com/2012/05/20/mvc-4-code-enhancements/
更多在这里：http: //evolpin.wordpress.com/2012/05/20/mvc-4-code-enhancements/
回答by Pavlo Neiman
Approach with TagWrap extension method. Code for your question would look like this:
使用 TagWrap 扩展方法的方法。您的问题的代码如下所示：
@using (Html.TagWrap("li", condition ? new { @class = "active" } : null))
{
var anchorAttrs = new Dictionary<string, object> { { "href", Url.Action("BusinessDetails", "Business") } };
if(condition)
{
anchorAttrs["style"] = "color: white; background-color: #08C; border: 1px solid #08C;";
}
using (Html.TagWrap("a", anchorAttrs))
{
<text>Business Details</text>
}
}
TagWrap extension methods
TagWrap 扩展方法
using Microsoft.AspNetCore.Mvc.ViewFeatures;
使用 Microsoft.AspNetCore.Mvc.ViewFeatures；
public static IDisposable TagWrap(this IHtmlHelper htmlHelper, string tagName, object data)
{
return htmlHelper.TagWrap(tagName, HtmlHelper.AnonymousObjectToHtmlAttributes(data));
}
public static IDisposable TagWrap(this IHtmlHelper htmlHelper, string tagName, IDictionary<string, object> data)
{
var tag = new TagBuilder(tagName);
tag.MergeAttributes(data);
htmlHelper.ViewContext.Writer.Write(tag.RenderStartTag());
return new DisposableAction(() =>
htmlHelper.ViewContext.Writer.Write(tag.RenderEndTag()));
}
Helper class used for rendering closing tag on Dispose
用于在 Dispose 上呈现结束标记的助手类
public class DisposableAction : IDisposable
{
private readonly Action DisposeAction;
public DisposableAction(Action action)
{
DisposeAction = action;
}
public void Dispose()
{
DisposeAction();
}
}
回答by spaark
Based on defrosts answer here an adaptation, taking an objectinstead of a string:
基于除霜回答这里的一个适应，采用一个object而不是一个string：
public static MvcHtmlString ConditionalAttr(this HtmlHelper helper, string attributeName, object value, Func<bool> condition)
{
if (string.IsNullOrEmpty(attributeName) || value == null)
{
return MvcHtmlString.Empty;
}
var render = condition != null ? condition() : true;
return render ?
new MvcHtmlString($"{attributeName}=\"{HttpUtility.HtmlAttributeEncode(value.ToString())}\"") :
MvcHtmlString.Empty;
}
This way you don't have to turn your other datatypes in strings before passing them, saving a fiew .ToString().
There is a difference tho: passing an empty string will still render.
As example:
这样您就不必在传递字符串之前将其他数据类型转换为字符串，从而节省了.ToString().
有一个区别：传递一个空字符串仍然会呈现。例如：
@Html.ConditionalAttr("data-foo", "", () => Model.IsFooNeeded)
// Ouput:
data-foo=""
