ViewState is a mechanism in ASP.NET Web Forms that allows you to preserve the state of server-side controls between postbacks. It is particularly useful for maintaining the values of controls on a web page when the page is submitted back to the server.

How ViewState Works

When a page is rendered, ASP.NET serializes the state of the controls and stores it in a hidden field called __VIEWSTATE. This hidden field is sent to the client as part of the page's HTML. When the page is posted back to the server, ASP.NET retrieves the ViewState data from the hidden field and restores the control values to their previous state.

Key Features of ViewState

• ViewState is specific to a page and is not shared across different pages.
• It is stored in a hidden field on the page, which can increase the page size.
• ViewState can be enabled or disabled for individual controls or the entire page.
• It is automatically managed by ASP.NET, requiring minimal developer intervention.

Sample Code Demonstrating ViewState

Below is a simple example that demonstrates how to use ViewState to maintain the value of a TextBox control across postbacks.

    <asp:TextBox ID="txtName" runat="server"></asp:TextBox>
    <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />
    <asp:Label ID="lblMessage" runat="server"></asp:Label>
    

Code-behind (C#):

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            // Initialize ViewState variable
            ViewState["User Name"] = string.Empty;
        }
    }

    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        // Store the TextBox value in ViewState
        ViewState["User Name"] = txtName.Text;

        // Retrieve the value from ViewState and display it
        lblMessage.Text = "Hello, " + ViewState["User Name"].ToString();
    }
    

How to Disable ViewState

If you want to disable ViewState for a specific control, you can set the EnableViewState property to false:

    <asp:TextBox ID="txtName" runat="server" EnableViewState="false"></asp:TextBox>
    

Conclusion

ViewState is a powerful feature in ASP.NET Web Forms that helps maintain the state of controls across postbacks. While it simplifies state management, developers should be mindful of its impact on page size and performance. Proper use of ViewState can lead to a better user experience in web applications.