Question

Like the title says.. why ?

I know why its required on the normal ASP.NET controls, there are numerous questions on SO about that.

But since you can only define .NET controls (no normal HTML markup) in the skin files, why is the runat="server" still required for every control in the skin file?

It has nothing to do with styles or themes.
Is there any reason why I still need ot add it to all controls in my skin files? Does anyone know what happens with it ‘behind the scenes’?

Answer 1

Again, you have to understand how server side languages work.

All ASP.NET tags are transformed to browser-understandable HTML (a browser has no notion of what an <asp:button> is, for instance) by a server side pre-processor before the page is rendered. This means that all controls/modules/anything served by ASP.NET that’s not just HTML needs to have these attributes.

I venture that the pre-processor was written originally to know what it needed to operate on based on the presence of that attribute. Otherwise it would have to process every tag even if it did nothing. It could’ve been written to just look for the namespace, but that would require extra processing.

A skin file is a special ASP.NET concept, for tags defined within the framework. Hence, it makes sense that these tags have to have the “runat=server”. MS could’ve written a special rule into their pre-processor such as “if it’s a skin file, assume it’s all ASP tags”…but such rules really don’t scale. Plus they’re bad documentation.

As a web developer, you should understand which of your tags are actually HTML and which are convenience tags provided by the framework. The "runat=server" attribute makes that delineation explicit.

You can add runat=”server” to plain HTML tags such as <input> but generally there’s little reason to and it’s a bad practice.

For portability moving forward, you may want to consider moving away from skin files and leveraging CSS. Attributes are very verbose for setting styles, which makes the end rendered pages larger (taking longer to load, providing poor user experience) and un-semantic.