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

Question

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.

Maisonette

Answer 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.

Maisonette

Unfortunately that's probably your best option right now. Another possible option is to try and directly call DefineSection, which is what "@section" gets translated down to. The problem is you can't put Markup inside a lambda in Razor v2 (something we're looking at for the future) so you're going to have to define your content in an @helper construct and call that helper from the DefineSection lambda. In the end, it might just end up being easier to do it the way you have. But we'll look at improving this in future versions! – Dunedin

Answer 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")
}

Caveator

Answer 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 :)

Lamarre

Answer 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>

Emotionalize

Answer 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>
    }
}

Proboscis

you want to put the IsSectionDefined in the Layout file and call rendersection with required = false – Proboscis

that's what i have currently, but it's outputting the div because the section is defined even if there's nothing in it. – Maisonette

what if the divs around it are wrapped with the IsSectionDefined ? – Proboscis

i modified the question and added the info about the layout. the section is defined even if the sidebar has nothing in it. I want to find a way to undefine the sidebar if the collection is empty. – Maisonette

The problem is the @section cannot be inside the if statement. – Maisonette

If the @section cannot be inside the if it will still be defined even if there is no content. that causes the <div></div> to be output. I guess there's no way around this. Thanks for your help. – Maisonette