ASP.Net MVC 3 Razor: Section Defined But Not Rendered Error

Question

I have the following layout template:

<div id="columns" class="@View.LayoutClass">
    <div id="mainColWrap">
        <div id="mainCol">
            @RenderBody()
        </div>
    </div>
    @if (View.ShowLeftCol){
    <div id="leftCol">
        @RenderSection("LeftCol", required: false)
    </div>
    }
    @if (View.ShowRightCol){
    <div id="rightCol">
        @RenderSection("RightCol", required: false)
    </div>
    }
</div>

If View.ShowLeftCol or View.ShowRightCol are set to false, I get the following error:

The following sections have been defined but have not been rendered for the layout page "~/Views/Shared/_Layout.cshtml": "RightCol".

I am trying to have a single layout template instead of trying to dynamically select a template at runtime. Is there a way to ignore this error and continue rendering? Can anyone think of another way to implement that would allow me to dynamically show/hide columns with Razor?

Thanks!

I don't understand what you're trying to accomplish. Your layout template should ALWAYS include @RenderSection. Then it's up to your individual Razor views whether they want to implement the section or not. — Portman
I'm allowing users to create webpages where they can control whether or not to display the left/right columns for their pages (e.g. Webpage.Title, Webpage.MetaKeywords, Webpage.ShowLeftCol, Webpage.ShowRightCol, Webpage.MainContent). It all runs through the same controller and view. I suppose I could handle it in the View, but then I have to put things like my standard left nav in every view instead of the layout template and I also have to pull in my layout divs (<div id="leftCol">). Hopefully that makes sense. Let me know if you need more clarification as to why I want this in the layout. — Sam
What going on~I meet this problem too. i've trid what Charles Gardner's suggestion,but it can't work. So anyone have the way to solve it? — user662156
What I ultimately ended up doing was allowing users to select from different views which either did or did not define the needed sections. E.g. - WebPage3Col.cshtml, WebPage2ColLeft.cshtml, ... This also gave me the flexibility to create completely customized views for certain scenarios that fit outside the initial project scope. — Sam
Once again, I find myself annoyed at having to jump through hoops to get what should have been the default behaviour to work. If this actually needed to be handled at all - we're adults here, after all - it could surely have been done better with some "option strict" flag to turn the all-sections-rendered validation on or off. Does C# force me to use every variable I declare in every conditional branch of my code? (Oh, did I say that out loud? I really hope I haven't given anyone any ideas.) — mwardm

Sam Sam · Accepted Answer · 2010-11-24T19:31:01

Was given a suggestion on the ASP.net forums that works.

Essentially, if I define @section LeftCol in my view template but don't run any code that calls RenderSection in my layout, I get the error because it doesn't get called when View.ShowLeftCol is false. The suggestion was to add an else block and essentially throw away whatever contents are in the LeftCol section.

@if (View.ShowLeftCol)
{ 
<div id="leftCol"> 
    @RenderSection("LeftCol", false) 
</div> 
}
else
{
    WriteTo(new StringWriter(), RenderSection("LeftCol", false));
}

Based on the concern raised about memory I decided to test the following out as well. Indeed it also works.

@if (showLeft)
{
    <section id="leftcol">
        <div class="pad">
            @RenderSection("LeftColumn", false)
        </div>
    </section>
}
else
{
    WriteTo(TextWriter.Null, RenderSection("LeftColumn", false));
}

Also, at the top of my page, this is my new logic for showLeft/showRight:

bool showLeft = IsSectionDefined("LeftColumn");
bool showRight = IsSectionDefined("RightColumn");
bool? hideLeft  = (bool?)ViewBag.HideLeft;
bool? hideRight = (bool?)ViewBag.HideRight;
if (hideLeft.HasValue && hideLeft.Value == true) { showLeft = false; }
if (hideRight.HasValue && hideRight.Value == true) { showRight = false; }

Someone else said it didn't work for them, but it worked like a charm for me.

ASP.Net MVC 3 Razor: Section Defined But Not Rendered Error

3 Answers