Understanding View State in ASP.NET
The HTTP protocol, the fundamental protocol of the World Wide Web and it is a stateless protocol. Each time you request a web page from a website, from the website’s perspective, you are a completely new person.
The ASP.NET Framework, however, manages to transcend this limitation of the HTTP protocol. For example, if you are binding the Gridview control with some data source(for example XML file), then the Gridview control displays the datasource across multiple page requests.
Consider below example where we have a Gridview control and button control. On Page Load, if postback is false we are assigning the XML file to the Gridview control as shown below.
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>ViewState Example</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:GridView ID="gv1" runat="server"></asp:GridView> <br />
<asp:Button ID="btn1" runat="server" Text="Click to Check ViewState" />
</div>
</form>
</body>
</html>
using System;
using System.Data;
using System.Web.UI;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (Page.IsPostBack == false)
{
DataSet ds = new DataSet();
ds.ReadXml("D:\\Employee.xml");
gv1.DataSource = ds.Tables[0];
gv1.DataBind();
}
}
}
The output display as shown below.
Now click the button control, surprisingly the gridview control is still have the XML datasource. This because asp.net storing the gridview control’s data in view state hidden field as shown below. You can find view state by selecting the view source option of any browser control.
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPDwULLTE3MzE0MTI2NzEPZBYCAgMPZBYCAgEPPCsADQIADxYEHgtfIURhd
GFCb3VuZGceC18hSXRlbUNvdW50AgRkDBQrAAIWCB4ETmFtZQUCSWQeCklzUmVhZE9ubHlo
HgRUeXBlGSsCHglEYXRhRmllbGQFAklkFggfAgUETmFtZR8DaB8EGSsCHwUFBE5hbWUWAmY
PZBYKAgEPZBYEZg8PFgIeBFRleHQFATFkZAIBDw8WAh8GBQFBZGQCAg9kFgRmDw8WAh8GBQ
EyZGQCAQ8PFgIfBgUBQmRkAgMPZBYEZg8PFgIfBgUBM2RkAgEPDxYCHwYFAUNkZAIED2QWB
GYPDxYCHwYFATRkZAIBDw8WAh8GBQE1ZGQCBQ8PFgIeB1Zpc2libGVoZGQYAQUDZ3YxDzwrAAk
BCAIBZJF8Jo1r1ZwLOViOzPnjGj2VKxht"
/>
By default, View State is enabled for every control in the ASP.NET Framework. If you change the background color of a Calendar control, the new background color is remembered across postbacks. If you change the selected item in a DropDownList, the selected item is remembered across postbacks. The values of these properties are automatically stored in View State.
View State is a good thing, but sometimes it can be too much of a good thing. The __VIEWSTATE hidden form field can become very large. Stuffing too much data into View State can slow down the rendering of a page because the contents of the hidden field must be pushed back and forth between the web server and web browser. In this scenario even you can disable the view state for total project or for individual page or individual control within the page by setting the EnableViewState property to false.
Disable the view state for total project by setting the EnableViewState property to false in web.config file.
<pagesenableViewState="false">
<controls>
...........
...........
</controls>
</pages>
Disable the view state for single page by setting the EnableViewState property to false in Page tag.
<%@ Page Language="C#" AutoEventWireup="true" EnableViewState="false" CodeFile="Default.aspx.cs" Inherits="_Default" %>
Disable the view state for individual control by setting the EnableViewState property to false of that control.
<asp:GridView ID="gv1" runat="server" EnableViewState="false"></asp:GridView>
