What Is View State And How It Works In ASP.NET

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm6.aspx.cs" Inherits="view_state.WebForm6" %>

<!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></title>
</head>
<body>
    <form id="form1" runat="server">
        <p>
            UserName: <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
            <br />
            Password: <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
            <br />
            <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Submit" />
            <asp:Button ID="Button3" runat="server" onclick="Button3_Click" Text="Restore" />
        </p>
    </form>
</body>
</html>

// Declaration of 'a' and 'b'
public string a, b;

protected void Button1_Click(object sender, EventArgs e)
{
    // TextBox1 and TextBox2 values are assigned to the variables 'a' and 'b'
    a = TextBox1.Text;
    b = TextBox2.Text;

    // After clicking on Button, TextBox values will be cleared
    TextBox1.Text = TextBox2.Text = string.Empty;
}

protected void Button3_Click(object sender, EventArgs e)
{
    // Values of variables 'a' and 'b' are assigned to TextBox1 and TextBox2
    TextBox1.Text = a;
    TextBox2.Text = b;
}

After the Submit button is clicked, the value of the user name and password is submitted to the server. We cannot restore the value again because after the postback, the instance of the control is destroyed, and on clicking the Restore Button, the server takes a new request, and the server cannot restore the value of the TextBox.

Features Of View State

These are the main features of the view state.

1. Retains the value of the Control after post-back without using a session.
2. Stores the value of Pages and Control Properties defined in the page.
3. Creates a custom View State Provider that lets you store View State Information in a SQL Server Database or in another data store.

Now, I am explaining the stored value in the View State, and the remaining steps are the same as the previous ones.

Now write this code.

protected void Button1_Click(object sender, EventArgs e)
{
    // Value of TextBox1 and TextBox2 is assigned to the ViewState
    ViewState["name"] = TextBox1.Text;
    ViewState["password"] = TextBox2.Text;

    // After clicking on Button, TextBox value will be cleared
    TextBox1.Text = TextBox2.Text = string.Empty;
}

protected void Button3_Click(object sender, EventArgs e)
{
    // If ViewState values are not null, assign them to TextBoxes
    if (ViewState["name"] != null)
    {
        TextBox1.Text = ViewState["name"].ToString();
    }

    if (ViewState["password"] != null)
    {
        TextBox2.Text = ViewState["password"].ToString();
    }
}

Output

After clicking on the Submit Button, the value of the user name and password is submitted in View State, and the View State stores the value of the user name and password during post-back.

After clicking on the Restore Button, we can get the value again. The Value must be retained during post-back, and the values are stored into a base 64 encoded string, and this information is then put into the View State Hidden Field.

Data Objects That Can be Stored in View state

1. String
2. Boolean Value
3. Array Object
4. Array List Object
5. Hash Table
6. Custom type Converters

Advantages of View State

1. Easy to Implement.
2. No server resources are required: The View State is contained in a structure within the page load.
3. Enhanced security features: It can be encoded and compressed or Unicode implementation.

Disadvantages of View State

1. Security Risk: The Information of View State can be seen in the page output source directly. You can manually encrypt and decrypt the contents of a Hidden Field, but It requires extra coding. If security is a concern then consider using a Server-Based state Mechanism so that no sensitive information is sent to the client.
2. Performance: Performance is not good if we use a large amount of data because View State is stored in the page itself and storing a large value can cause the page to be slow.
3. Device limitation: Mobile Devices might not have the memory capacity to store a large amount of View State data.
4. It can store values for the same page only.

When We Should Use View State

1. When the data to be stored is small.
2. Try to avoid secure data.

How to Enable and Disable View State

You can enable and disable View State for a single control as well as at the page level. To turn off View State for a single control, set the EnableViewState property of that control to false.

TextBox1.EnableViewState=false;

To turn off the View State for an entire page, we need to setEnableViewState to false of the page directive, as shown below.

<%PageLanguage="C#"EnableViewState="false";

To enable the same, you need to use the same property just set it to "True".

View State Security

View State Data is stored in the form of Base 64 encoding, but it is not very secure. Anyone can easily break it. So there are the following 2 options,

1. Using the MAC for Computing the View State Hash Value
   Generally, the larger MAC key is used to generate a Hash Key. When the key is auto-generated, then ASP.NET uses SHA-1 encoding to create a larger key. Those keys must be the same for all the servers. If the key is not the same and the page is posted back to a different server than the one that created the page, then the ASP.NET Page Framework raises an exception. We can enable it by using.

   <%PageLanguage="C#"EnableViewState="true"EnableViewStateMac="true";

2. Encryption
   By using MAC Encoding, we cannot prevent the viewing of the data, so to prevent the viewing, we transmit the page over SSL and encrypt the View State Data. To encrypt the data, we have the ViewStateEncryptionMode Property, and it has the following 3 options.
   • Always: Encrypt the data Always.
   • Never: Encrypt the data Never.
   • Auto: Encrypt any Control request, especially for Encryption

We can enable it by using.

1. <%PageLanguage="C#"EnableViewState="trueViewStateEncryptionMode="Always"