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Posted 30 Jun 2009

Access ViewState Across Pages

, 30 Jun 2009 CPOL
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This article demonstrates how we can share ViewState across pages


Before I start this article, let me ask you something. Is it possible to access the ViewState variable of one page on another page? I don't know what your answer is. Well, frankly speaking, my answer was also "NO" before writing this article as it is said that ViewState is page specific.


ViewState is a very misunderstood animal. It is said that ViewState is Page specific; that means, it is available only on the same page on which it was created. Once you redirect to another page, the previous page's viewstate is no longer accessible. But that is not true.

Using the Code

Yes, we can access the viewstate variables across pages. This is only possible if Cross Page Posting or Server.transfer is used to redirect the user to other page. If Response.redirect is used, then ViewState cannot be accessed across pages.

Before you continue reading this article, please read these articles on Cross Page Posting and Server.transfer.

Ok, so all set now... I will demonstrate this using the demo created by me. You can download the demo from the link at the top of this article.

I have created two *.aspx pages named:

  1. ViewStateContainer.aspx: This page sets the ViewState variable and transfers the user to another page using Server.transfer.
  2. AccessViewState.aspx: This page accesses the ViewState variable of ViewStateContainer.aspx page.

This is the code of ViewStateContainer.aspx page:

public partial class ViewStateContainer : System.Web.UI.Page
    protected void Page_Load(object sender, EventArgs e)
        ViewState["Page1"] = "Page1 ViewState";

    public StateBag ReturnViewState()
        return ViewState;

As you can see, I have set a ViewState variable in Page Load and transfer the user to AccessViewState.aspx page using the Server.transfer() method.

This page also contains a method ReturnViewState() which actually returns the ViewState of this page to the calling function. The return type of the method is StateBag class.

StateBag class: This class is the primary storage mechanism for all HTML and Web server controls. It stores attribute/value pairs as strings associated with the control. It tracks changes to these attributes only after the OnInit method is executed for a page request, and saves the changes to the page's or control's viewstate.

Now let's take look at AccessViewState.aspx Page code:

public partial class AccessViewState : System.Web.UI.Page
    private StateBag PreviousPageViewState
            StateBag returnValue = null;
            if (PreviousPage != null)
                Object objPreviousPage = (Object)PreviousPage;
                MethodInfo objMethod = objPreviousPage.GetType().GetMethod
                return (StateBag)objMethod.Invoke(objPreviousPage, null);
            return returnValue;

    protected void Page_Load(object sender, EventArgs e)
        if (PreviousPage != null)
            if (PreviousPageViewState != null)
                Label1.Text = PreviousPageViewState["Page1"].ToString();

Whenever we use Server.transfer or Cross Page Posting, We can get the previous page object via PreviousPage property. Using Previous Page, we can find the controls of the previous page. For example, one can access Label control placed in ViewStateContainer Page in current Page.

Looking at the code, I have created a PreviousPageViewState property in this page, which returns the previous page's ViewState. It first checks whether PreviousPage is null or not, if it's not null, then it creates an object of the previous page. Now using Reflection, we can invoke the method of the previous class. Using MethodInfo class, I have invoked the ReturnViewState() method of ViewStateContainer Page.

In Page_Load event, I am able to access the ViewState variable of ViewStateContainer Page. You can access all the viewstate variables set in ViewStateContainer Page.



  • 30th June, 2009: Initial post


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Talking Dotnet
Technical Lead
India India
I am an experienced Software Developer with 8+ years of hands-on experience working with Microsoft .NET technology (ASP.NET, C#, VB.NET,SQL Server).

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Comments and Discussions

QuestionWhy use state at all? Pin
Tragdor30-Jun-09 5:39
memberTragdor30-Jun-09 5:39 
The previous statement was Why use ViewState?
Well you probably want to access information from the previous page (remember web controls are pages too). All server controls are data bound to information that you do not want to loose. Placing the iSerializable data into ViewState is very convenient and I have even gone as far as using ASP.NET State Providers to keep viewstate away from the page contents.

It is very helpful to only hit a database once for information, and then update the viewstate until you are ready to save the changes.

ViewState is a powerful tool and helps keep your web pages in sync.

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