Practical .NET

Errors on Unused Sections in ASP.NET MVC Views

If you don't use a section in a View, then you'll get an error. But you may not find out until it's too late.

First, let me be clear: This is more of a warning than a tip.

A typical ASP.NET MVC Layout View will have a number of RenderSection methods that invoke sections defined in the View being processed. However, if you have a section in a View that isn't used, ASP.NET MVC will raise an error when processing your View (specifically, the error, "The following sections have been defined but have not been rendered for the layout page"). This check is done at runtime, not compile time, so you won't find the problem until you visit the relevant page (hopefully, this will happen during testing and not in production).

You won't get this error if you include an unused section in a Partial View. However, that's because ASP.NET MVC ignores all sections in Partial Views. You might assume you'll never have this error except, perhaps, if you spell the name of a section wrong, either in the Layout View or in the View itself.

However, one of my clients had, in their Layout View, put a RenderSection inside an If...Then block. When the test came out False, the RenderSection was skipped, the corresponding section wasn't used, and ASP.NET MVC generated the "following sections have been defined but" message.

Whenever you make a change to a View, no matter how trivial, it's always a good idea to visit that page before releasing it under all possible conditions. Always.

About the Author

Peter Vogel is a system architect and principal in PH&V Information Services. PH&V provides full-stack consulting from UX design through object modeling to database design. Peter tweets about his VSM columns with the hashtag #vogelarticles. His blog posts on user experience design can be found at http://blog.learningtree.com/tag/ui/.

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