Is there a way to make a @section optional with the asp.net mvc Razor ViewEngine?

问题

I have a Page.cshtml similar to the following (that does not work):

@{
    Layout = "../Shared/Layouts/_Layout.cshtml";
    var mycollection = (ViewBag.TheCollection as IQueryable<MyCollectionType>);
}

<h2>@ViewBag.Title</h2>

content here

@if (mycollection != null && mycollection.Count() > 0)
{    
    @section ContentRight
    {    
        <h2>
            Stuff
        </h2>
        <ul class="stuff">
            @foreach (MyCollectionType item in mycollection )
            {
                <li class="stuff-item">@item.Name</li>
            }
        </ul>
    }
}

As I said, this does not work. I want to not define the section if there's nothing in the collection. Is there any way to have something like this work? If not, what are my other options? I'm very new to this Razor ViewEngine.

Edit

In my layout i have:

@if(IsSectionDefined("ContentRight")) 
{
    <div class="right">
        RenderSection("ContentRight")
    </div>
}

what i don't want is the div to output when the section is empty.

回答1:

I ended up doing something a little hacky to get it working how I needed it.

on my page i have:

@{
    Layout = "../Shared/Layouts/_Layout.cshtml";
    var mycollection = (ViewBag.TheCollection as IQueryable<MyCollectionType>);
    ViewBag.ShowContentRight = mycollection != null && mycollection.Count() > 0;
}

then in my layout i have:

@if(IsSectionDefined("ContentRight") && (ViewBag.ShowContentRight == null ||ViewBag.ShowContentRight == true)) 
{
    <div class="right">
        RenderSection("ContentRight")
    </div>
}
else if(IsSectionDefined("ContentRight"))
{
    RenderSection("ContentRight")
}

If the section is defined it has to be rendered, but if there's no content i dont want the <div>s

If there's a better way i'd like to know.

回答2:

The renderer is expecting the method to be called sometime in the layout file. You can spoof the renderer and use "global" conditionals (think login).

@{
    ViewBag.content = RenderBody();
}
@if (Request.IsAuthenticated) {
        @ViewBag.content;
} 
else {
        @Html.Partial("_LoginPartial")
}

回答3:

Extension method with private static readonly field info for perf:

private static readonly FieldInfo RenderedSectionsFieldInfo = typeof(WebPageBase).GetField("_renderedSections", BindingFlags.Instance | BindingFlags.NonPublic);

public static void EnsureSectionsAreRegisteredAsRendered(this WebPageBase webPageBase, params string[] sectionNames)
{
    var renderedSections = RenderedSectionsFieldInfo.GetValue(webPageBase) as HashSet<string>;
    if (renderedSections == null)
    {
        throw new WebCoreException("Could not get hashset from private field _renderedSections from WebPageBase");    
    }
    foreach (var sectionName in sectionNames)
    {
        if (!renderedSections.Contains(sectionName))
        {
            renderedSections.Add(sectionName);
        }
    }
}

In your cshtml:

@{ this.EnsureSectionsAreRegisteredAsRendered("SectionName1", " SectionName2", "…"); }

Yes, yes, yes.... I know.... bad reflection! Use at your own risk :)

回答4:

I use the following method in my view base class (from this excellent blog post http://haacked.com/archive/2011/03/05/defining-default-content-for-a-razor-layout-section.aspx/):

public HelperResult RenderSection(string name, Func<dynamic, HelperResult> defaultContents)
{
    if (IsSectionDefined(name))
    {
        return RenderSection(name);
    }
    return defaultContents(null);
}

If you don't have a view base class, I recommend one because it lets you add all sorts of little extra functionality to your views. Just create a class with the following signature: public abstract class MyViewPage<T> : WebViewPage<T> and then set it in your web.config:

<system.web.webPages.razor>
  <pages pageBaseType="MyViewPage">
    ...
  </pages>
</system.web.webPages.razor>

回答5:

You can wrap your whole section in an if statement with IsSectionDefined

Layout.cshtml:

@if (IsSectionDefined("ContentRight"))
{
    <div>
    @RenderSection(name: "ContentRight", required: false)
    </div>
}

Your cshtml page:

@section ContentRight
{    
    @if (mycollection != null && mycollection.Count() > 0)
    {   
    <h2>
        Stuff
    </h2>
    <ul class="stuff">
        @foreach (MyCollectionType item in mycollection )
        {
            <li class="stuff-item">@item.Name</li>
        }
    </ul>
    }
}

来源：https://stackoverflow.com/questions/4903289/is-there-a-way-to-make-a-section-optional-with-the-asp-net-mvc-razor-viewengine