ASP.NET - Render Hidden Fields at the Top of a Form with .NET 3.5 SP1

I just came across a nice feature in ASP.NET 3.5 SP1 (currently in Beta) that I didn’t realize was included.  It’s always nice to discover hidden gems from time to time.  With ASP.NET 1.0, 1.1, 2.0 and 3.5 applications if a user or JavaScript function tried to do a postback before all of the ViewState and EventValidation data was loaded in the browser, a ViewState MAC validation error could be raised by the server.

In ASP.NET 3.5 SP1 Microsoft provides a new attribute on the <pages> element in web.config that now allows all hidden fields to be rendered at the top of a form rather than at the bottom which can help to avoid the ViewState MAC validation error when people perform a postback operation before the page has finished loading.  The attribute is named renderAllHiddenFieldsAtTopOfForm (which does what it says) and defaults to a value of true.  .NET 3.5 SP1 is currently in beta but once it’s officially released the new attribute is definitely a nice enhancement to the ASP.NET framework.

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