JumpStart # 3 – ViewStateMode in ASP.Net 4.0

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<%@ Page Language="C#" EnableViewState="true"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">
    /* ViewStateMode - 
     * 1) It is a new feature in ASP.Net 4.0. Using this we have explicit control on the controls
     *    which participate in viewstate, thereby preventing unnecessary information going into
     *    viewstate during postbacks.
     * 2) In previous versions of ASP.Net, you can disabled viewstate for complete page by setting
     *    EnableViewState="false" in @Page directive, the same can be used in ASP.Net 4.0, but for
     *    more robost control on viewstate we got to use ViewStateMode.
     * 3) Once we disable viewstate for complete page using EnableViewState, we cannot enable it for
     *    any other control used in that page, but using ViewStateMode you can achieve the same.
     * 4) You can disable viewstate of the page by setting ViewStateMode="Disabled", and still you can
     *    enable viewstate for child controls using theie ViewStateMode="Enabled".
     * 5) ViewStateMode can have three values - Enabled, Disabled, Inherit. First two values are self
     *    explanatory, Inherit means the control will inherit its ViewStateMode from its container.
     * 6) The default ViewStateMode of Page is Enabled and for that of a control is Inherit. 
     * 7) ViewStateMode can be used in @Page directive too.
     * 8) One must be careful in implementing this feature, as it may result unwanted results if it is
     *    not used in appropriate ways.
     */
    protected void Page_Load(object sender, EventArgs e)
    {
        Page.ViewStateMode = System.Web.UI.ViewStateMode.Disabled;

        if (!IsPostBack)
        {
            Label1.Text = "John";
            Label2.Text = "Chris";
            Label3.Text = "Bob";
            Label4.Text = "Adam";
            Label5.Text = "Scott";
        }
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        
        <!-- Label Will not hold its value after postback -->
        <asp:Label ID="Label1" ViewStateMode="Disabled" runat="server" Text="Label1"></asp:Label>
        
        <!-- Label Will hold its value after postback -->
        <asp:Label ID="Label2" ViewStateMode="Enabled" runat="server" Text="Label2"></asp:Label>
        
        <!-- Label Will not hold its value after postback, as its container's viewstate is disabled -->
        <asp:PlaceHolder ID="PlaceHolder1" ViewStateMode="Disabled" runat="server">
            <asp:Label ID="Label3" ViewStateMode="Inherit" runat="server" Text="Label3"></asp:Label>
        </asp:PlaceHolder>
        
        <!-- Label Will hold its value after postback, as its container's viewstate is Enabled -->
        <asp:PlaceHolder ID="PlaceHolder2" ViewStateMode="Enabled" runat="server">
            <asp:Label ID="Label4" ViewStateMode="Inherit" runat="server" Text="Label4"></asp:Label>
        </asp:PlaceHolder>
        
        <!-- Label Will hold its value after postback, even though its container's viewstate is 
             disabled, as label's viewstate in enabled -->
        <asp:PlaceHolder ID="PlaceHolder3" ViewStateMode="Disabled" runat="server">
            <asp:Label ID="Label5" ViewStateMode="Enabled" runat="server" Text="Label5"></asp:Label>
        </asp:PlaceHolder>        
        
        <asp:Button ID="Button1" runat="server" Text="PostBack" />
    </div>
    </form>
</body>
</html>

OUTPUT -

Before Postback -                                                      After PostBack -

Before Postback - ViewStateMode                     After Postback - ViewStateMode

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  • abhilasha

    great help in understanding ViewStateMode