为什么在剃刀声明@helper方法HtmlHelper的实例为空? [英] Why is the HtmlHelper instance null in a Razor declarative @helper method?
问题描述
使用MVC 3 RTM我得到一个奇怪的的NullReferenceException
:
Using MVC 3 RTM I'm getting a strange NullReferenceException
:
@helper TestHelperMethod() {
var extra = "class=\"foo\"";
<div @Html.Raw(extra)></div>
}
原来, HTML
(类型为的HtmlHelper
)的空
。
我以前从来没有在常规视图看到了这一点。我开始尝试在剃刀(到目前为止,他们似乎有点有限的)声明辅助方法,我很被我所看到的在这里难住了。
I've never seen this before in a regular view. I'm starting to experiment with declarative helper methods in Razor (so far they seem a little limited) and I'm quite stumped by what I'm seeing here.
推荐答案
这是一个<一href="http://stackoverflow.com/questions/4451287/razor-declarative-html-helpers/4453637#4453637">known这些助手的限制的。一种可能是把它作为参数:
That's a known limitation of those helpers. One possibility is to pass it as parameter:
@helper TestHelperMethod(HtmlHelper html) {
var extra = "class=\"foo\"";
<div@html.Raw(extra)></div>
}
另一种可能性是写的助手作为扩展方式:
Another possibility is to write the helper as an extension method:
public static class HtmlExtensions
{
public static MvcHtmlString TestHelperMethod(this HtmlHelper)
{
var div = new TagBuilder("div");
div.AddCssClass("foo");
return MvcHtmlString.Create(div.ToString());
}
}
然后:
@Html.TestHelperMethod()
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