Postback not working with ASP.NET Routing (Validation of viewstate MAC failed)

Question

I'm using the ASP.NET 3.5 SP1 System.Web.Routing with classic WebForms, as described in http://chriscavanagh.wordpress.com/2008/04/25/systemwebrouting-with-webforms-sample/

All works fine, I have custom SEO urls and even the postback works. But there is a case where the postback always fails and I get a:

Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

Here is the scenario to reproduce the error:

1. Create a standard webform mypage.aspx with a button
2. Create a Route that maps "a/b/{id}" to "~/mypage.aspx"
3. When you execute the site, you can navigate http://localhost:XXXX/a/b/something the page works. But when you press the button you get the error. The error doen't happen when the Route is just "a/{id}".

It seems to be related to the number of sub-paths in the url. If there are at least 2 sub-paths the viewstate validation fails.

You get the error even with EnableViewStateMac="false".

Any ideas? Is it a bug?

Thanks

Answer 1

I worked around this by having my view user control inherit from this class instead of ViewUserControl<T> (it's kind of a patch for RenderView). It did the trick for me, hopefully it works for you too.

public class ViewUserControlWithoutViewState<T> : ViewUserControl<T> where T : class {
    protected override void LoadViewState(object savedState) {}

    protected override object SaveControlState() {
        return null;
    }

    protected override void LoadControlState(object savedState) {}

    protected override object SaveViewState() {
        return null;
    }

    /// <summary>
    /// extracted from System.Web.Mvc.ViewUserControl
    /// </summary>
    /// <param name="viewContext"></param>
    public override void RenderView(ViewContext viewContext) {
        viewContext.HttpContext.Response.Cache.SetExpires(DateTime.Now);
        var containerPage = new ViewUserControlContainerPage(this);
        ID = Guid.NewGuid().ToString();
        RenderViewAndRestoreContentType(containerPage, viewContext);
    }

    /// <summary>
    /// extracted from System.Web.Mvc.ViewUserControl
    /// </summary>
    /// <param name="containerPage"></param>
    /// <param name="viewContext"></param>
    public static void RenderViewAndRestoreContentType(ViewPage containerPage, ViewContext viewContext) {
        string contentType = viewContext.HttpContext.Response.ContentType;
        containerPage.RenderView(viewContext);
        viewContext.HttpContext.Response.ContentType = contentType;
    }

    /// <summary>
    /// Extracted from System.Web.Mvc.ViewUserControl+ViewUserControlContainerPage
    /// </summary>
    private sealed class ViewUserControlContainerPage : ViewPage {
        // Methods
        public ViewUserControlContainerPage(ViewUserControl userControl) {
            Controls.Add(userControl);
            EnableViewState = false;
        }

        protected override object LoadPageStateFromPersistenceMedium() {
            return null;
        }

        protected override void SavePageStateToPersistenceMedium(object state) {}
    }
}

I blogged about this some time ago.