The size of the ViewState for a page should be minimal for a better performance in page rendering.  Remember that the data in the ViewState makes a round trip and incurs more network bandwidth usage.  Therefore, ViewState should always be used judiciously.  For pages and controls that do not require a post back at all, set the EnableViewState property of the page or the control of the page to false.  It is always preferable to keep the ViewState out of the aspx page for performance improvements of the web application.  To accomplish this, the methods SavePageStateToPersistenceMedium and LoadPageStateFromPersistenceMedium can be used.  Use the following in the web.config or the machine.config file to disable ViewState for all the pages in a particular application or for all applications.

Listing 8

<Pages enableViewState="false"/>

Note that only controls contained within a <form runat=server> tag in the .aspx page can store ViewState.  Further, even if ViewState for a page is disabled, still the page itself saves about 20 bytes of information into ViewState to distribute post back data and ViewState values to the correct controls on post back.  So, for pages that do not post back at all, remove the runat="server" tag completely for a reduction of the page size by an amount of 20 bytes.  This reduction can be substantial for a number of such pages of the application running over the network.  ViewState should only be enabled for pages and controls that use it.  Avoid using ViewState for controls like the DataGrid and the DataRepeater as the ViewState size for these controls is quite huge.  Setting the EnableViewState properties or these controls to false would result in a huge reduction of the size of the rendered html and hence the bandwidth.

During the testing phases of an application, the ViewState size should be tested.  I am giving a code below that can detect the size of the ViewState of a page with ease.  I have created a MasterPageBase class that all the other pages in the application need to inherit.  The code for the class is as shown below.

Listing 9

public class MasterPageBase: System.Web.UI.Page
{
  protected override void OnPreRender(EventArgs e)
  {
    object viewStateObject = HttpContext.Current.Request["__VIEWSTATE"];
    if (viewStateObject == null)
      HttpContext.Current.Trace.Warn("The ViewState Size is:", "0");
    else
      HttpContext.Current.Trace.Warn("The ViewState Size is:",
        HttpContext.Current.Request["__VIEWSTATE"].Length.ToString());
    base.OnPreRender(e);
  }
}