Viewstate Compression Issues

Question

I'm currently fighting with the .NET Viewstate and it is starting to wear me down. Having found that some of the pages in one of our applications is made up of around 80% viewstate I have looked into reducing this where I can.

I have looked at (and am happy with) disabling viewstate for controls that do not need it (labels, buttons etc) and have made some small gains here.

I'm now looking at viewstate compression and while I can demonstrate a 40-50% decrease in size it does not seem to be playing well with my application.

Scenario: Page contains a few dropdown lists, a button and a Grdiview (hence the need to deal with the ViewState!). When the page loads the DDLs are populated and default selections are made. Pressing the OK button results in the Gridview being populated as expected.

Now the problem: With Viewstate Compression enabled, if the user changes the selected items in the DDLs before clicking the OK button they will get a 'Required Field Validator' error indicating that a selection has not been made in one of the DDLs - but this is not the case! Disabling the compression code removes the problem and the page operates as expected (i.e. as it has for months!).

Could the problem be down to the viewstate now being stored in a key other than __VIEWSTATE [the code that I have seen use different key names - VSTATE for instance).

My page sources look like this;

Page Source with Compression (note the empty __VIEWSTATE key):

<div>
<input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
<input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />
<input type="hidden" name="__LASTFOCUS" id="__LASTFOCUS" value="" />
<input type="hidden" name="__VSTATE" id="__VSTATE" value="H4sIAAAAAEAO29B2AcSZYlJ
.
.
MKd2afqdaImFR5UiFXVyQPwLPA//8xt+pMsSQ8vlOklcoNgmZfJd8hHvk6/S/7UbxxAJTjzZfp6Qcm039
h3d3dvvPO7/Oa/7i57uemj1H2a/gw5lJQ+ySjFRtPZUL7A/3o2ImFR5UiFXVyLPA+38At70F1EkwAAA=" />
<input type="hidden" name="__VIEWSTATE" id="
__VIEWSTATE" value="" />
</div>

Page Source without Compression:

<div>
<input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
<input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />
<input type="hidden" name="__LASTFOCUS" id="__LASTFOCUS" value="" />
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPDwUKMTYxOTM1NDg4N
A9kFgJmD2QWAgIDD2QWAgIFD2QWAmYPZBYKAgEPZBYIAgcPZBYCAgMPDxYCHgRUZXh0BRdEYXduQyBbY2hhbm
dlIHBhc3N3b3JkXWRkAgkPFgIeB1Zpc2libGVoFgQCAQ8PFgIfAAUFQWRtaW5kZAIDDw8WAh8ABQUxNDoyNGR
.
.
.
.
.
.
kAgsPDxYEHwAFWVNlbGVjdGVkIFNlcnZpY2UgVXNlcjogPGEgY2xhc3M9J3N1U2VsZWN0b3InIGhyZWY9J2xp
c3RzZXJ2aWNldXNlcnMuYXNweCc+PGI+bm9uZTwvYj48L2E+HwFoZGQCDw8QZGQWAGQCBQ8UKwADZDwrABQEA
BYSHg9QYXJlbnRJdGVtQ2xhc3MFC2lnbW5fUGFyZW50HhdUb3BMZXZlbFBhcmVudEl0ZW1DbGFzcwUTaWdtbl
Ub3BFBhcmVudB4KSlNGaWxlTmFtZWUeFlRvcExldmVsSG92ZXJJdGVtQ2xhc3MFNGlnbW5fVG9wTGV"     
/>
</div>

How does .NET know where the VIEWSTATE is stored and does it know that i have moved it?

Do I need to make any other changes to my code apart from implementing SavePageStateToPersistenceMedium and LoadPageStateFromPersistenceMedium?

Answer 1

hey viewstate compression works for me without any problems. basically i have a baseclass for all my aspx pages which use viewstate. even i am using a different viewstate key to save my viewstate. however you have to override 2 methods for this:

1) - to save viewstate 2) - to load viewstate

as long as you are doing this, you should have no problems. see below code which i am using for my baseclass

using System;
using System.IO;
using System.Web.UI;

namespace XC.UI.WebForms
{

    public class PageBase : System.Web.UI.Page
    {

        protected override object LoadPageStateFromPersistenceMedium()
        {
            string viewState = Request.Form["__VSTATE"];
            byte[] bytes = Convert.FromBase64String(viewState);
            bytes = XC.Common.ViewStateHelper.Decompress(bytes);
            LosFormatter formatter = new LosFormatter();
            return formatter.Deserialize(Convert.ToBase64String(bytes));
        }

        protected override void SavePageStateToPersistenceMedium(object viewState)
        {
            LosFormatter formatter = new LosFormatter();
            StringWriter writer = new StringWriter();
            formatter.Serialize(writer, viewState);
            string viewStateString = writer.ToString();
            byte[] bytes = Convert.FromBase64String(viewStateString);
            bytes = XC.Common.ViewStateHelper.Compress(bytes);
            ClientScript.RegisterHiddenField("__VSTATE", Convert.ToBase64String(bytes));
        }

    }

}