RazorExtensions Templated Razor Delegates

原文发布时间为：2011-04-27 —— 来源于本人的百度文章 [由搬家工具导入]

Templated Razor Delegates

David Fowler turned me on to a really cool feature of Razor I hadn’t realized made it into 1.0, Templated Razor Delegates. What’s that? I’ll let the code do the speaking.

@{
Func<dynamic, object> b = @<strong>@item</strong>;
}
<span>This sentence is @b("In Bold").</span>

That could come in handy if you have friends who’ll jump on your case for using the bold tag instead of the strong tag because it’s “not semantic”. Yeah, I’m looking at you Damian . I mean, don’t both words signify being forceful? I digress.

Note that the delegate that’s generated is a Func<T, HelperResult>. Also, the @item parameter is a special magic parameter. These delegates are only allowed one such parameter, but the template can call into that parameter as many times as it needs.

The example I showed is pretty trivial. I know what you’re thinking. Why not use a helper? Show me an example where this is really useful. Ok, you got it!

Suppose I wrote this really cool HTML helper method for generating any kind of list.

publicstaticclassRazorExtensions {
publicstaticHelperResult List<T>(thisIEnumerable<T> items,
Func<T, HelperResult> template) {
returnnewHelperResult(writer => {
foreach(var iteminitems) {
template(item).WriteTo(writer);
}
});
}
}

This List method accepts a templated Razor delegate, so we can call it like so.

@{
var items = new[] { "one", "two", "three" };
}

<ul>
@items.List(@<li>@item</li>)
</ul>

As I mentioned earlier, notice that the argument to this method, @<li>@item</li> is automatically converted into a Func<dynamic, HelperResult> which is what our method requires.

Now this List method is very reusable. Let’s use it to generate a table of comic books.

@{
var comics = new[] {
new ComicBook {Title = "Groo", Publisher = "Dark Horse Comics"},
new ComicBook {Title = "Spiderman", Publisher = "Marvel"}
};
}

<table>
@comics.List(
@<tr>
<td>@item.Title</td>
<td>@item.Publisher</td>
</tr>)
</table>

This feature was originally implemented to support the WebGrid helper method, but I’m sure you’ll think of other creative ways to take advantage of it.

If you’re interested in how this feature works under the covers, check out this blog post by Andrew Nurse.

http://haacked.com/archive/2011/02/27/templated-razor-delegates.aspx