What's the point of the Web.config's system.web/Pages/Namespaces Tag?

Question

Regardless of whether my machines's root web config (the one in Windows/Microsoft.NET/...) contains system.web/pages/namespaces/add elements, it still is demanded that I include using statements atop each aspx.cs CodeBehind file. Why? Shouldn't it compile and not complain that it cannot understand what a Page is? After all, <add namespace="System.Web" /> exists in the root web.config!

Answer 1

The system.web/pages/namespaces/add element is for .ASPX files, normal .CS files (including .ASPX.CS) still need to do proper using as there is no pre-processing of the source before compilation. So .ASPX.CS must be valid CS file including all using Namespace declarations.

Answer 2

This adds namespaces to your aspx and ascx files so that you do not have to include <%@ Import Namespace="MyNameSpace" %> statements.

From the documentation on MSDN:

The namespaces element defines a collection of import directives to use during assembly pre-compilation. This attribute corresponds to the @ Import directive on an ASP.NET page. The @ Import directive allows you to specify namespaces that are automatically imported into all pages of an application.

Your codebehind is in no way affected by these web.config entries.

Answer 3

The other answers here indicate that this web.config setting only affects the ASPX pages, and not the code-behind pages such as ASPX.CS. I have just tested this in an ASP.NET website targeting .NET 4.0, and have found this to be true for C# pages, but not true for VB pages.

Adding a namespace into the web.config settings removed the requirement to list it at the top of every ASPX.VB page.

I would be interested in any theories why this might be. I would have thought it would work for both ASPX.CS and ASPX.VB code behind files.