HiddenField Class (System.Web.UI.WebControls)

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Microsoft Visual Studio 2008/.NET Framework 3.5

Other versions are also available for the following:

.NET Framework Class Library

HiddenField Class

Represents a hidden field used to store a non-displayed value.

Namespace: System.Web.UI.WebControls
Assembly: System.Web (in System.Web.dll)

Syntax

Visual Basic (Declaration)

<ControlValuePropertyAttribute("Value")> _
<AspNetHostingPermissionAttribute(SecurityAction.InheritanceDemand, Level := AspNetHostingPermissionLevel.Minimal)> _
<AspNetHostingPermissionAttribute(SecurityAction.LinkDemand, Level := AspNetHostingPermissionLevel.Minimal)> _
Public Class HiddenField _
    Inherits Control _
    Implements IPostBackDataHandler

Visual Basic (Usage)

Dim instance As HiddenField

[ControlValuePropertyAttribute("Value")]
[AspNetHostingPermissionAttribute(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermissionAttribute(SecurityAction.LinkDemand, Level = AspNetHostingPermissionLevel.Minimal)]
public class HiddenField : Control, 
    IPostBackDataHandler

Visual C++

[ControlValuePropertyAttribute(L"Value")]
[AspNetHostingPermissionAttribute(SecurityAction::InheritanceDemand, Level = AspNetHostingPermissionLevel::Minimal)]
[AspNetHostingPermissionAttribute(SecurityAction::LinkDemand, Level = AspNetHostingPermissionLevel::Minimal)]
public ref class HiddenField : public Control, 
    IPostBackDataHandler

JScript

public class HiddenField extends Control implements IPostBackDataHandler

ASP.NET

<asp:HiddenField />

Remarks

The HiddenField control is used to store a value that needs to be persisted across posts to the server. It is rendered as an <input type= "hidden"/> element.

Normally view state, session state, and cookies are used to maintain the state of a Web Forms page. However, if these methods are disabled or are not available, you can use the HiddenField control to store state values.

To specify the value for a HiddenField control, use the Value property. You can provide a routine that gets called every time the value of the HiddenField control changes between posts to the server by creating an event handler for the ValueChanged event.

Examples

The following example demonstrates how to use the HiddenField control to store the value of a TextBox control between posts to the server.

Security Note:
This example has a text box that accepts user input, which is a potential security threat. By default, ASP.NET Web pages validate that user input does not include script or HTML elements. For more information, see Script Exploits Overview.

Visual Basic

<%@ Page language="VB" %>

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

  Sub ValueHiddenField_ValueChanged(ByVal sender As Object, ByVal e As EventArgs)

    ' Display the value of the HiddenField control.
    Message.Text = "The value of the HiddenField control is " & ValueHiddenField.Value & "."

  End Sub

</script>

<html  >
    <head runat="server">
    <title>HiddenField Example</title>
</head>
<body>
        <form id="Form1" runat="server">

            <h3>HiddenField Example</h3>

            Please enter a value and click the submit button.<br/>

            <asp:textbox id="ValueTextBox"
              runat="server"/>

            <br/>  

            <input type="submit" name="SubmitButton"
             value="Submit"
             onclick="PageLoad()" />

            <br/>

            <asp:label id="Message" runat="server"/>    

            <asp:hiddenfield id="ValueHiddenField"
              onvaluechanged="ValueHiddenField_ValueChanged"
              value="" 
              runat="server"/>

        </form>
    </body>
</html>

<script type="text/javascript">

  <!--
  function PageLoad()
  {

    // Set the value of the HiddenField control with the
    // value from the TextBox.
    Form1.ValueHiddenField.value = Form1.ValueTextBox.value;

  }
  -->

</script>

<%@ Page language="C#" %>

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

  void ValueHiddenField_ValueChanged (Object sender, EventArgs e)
  {

    // Display the value of the HiddenField control.
    Message.Text = "The value of the HiddenField control is " + ValueHiddenField.Value + ".";

  }

</script>

<html  >
    <head runat="server">
    <title>HiddenField Example</title>
</head>
<body>
        <form id="Form1" runat="server">

            <h3>HiddenField Example</h3>

            Please enter a value and click the submit button.<br/>

            <asp:Textbox id="ValueTextBox"
              runat="server"/>

            <br/>  

            <input type="submit" name="SubmitButton"
             value="Submit"
             onclick="PageLoad()" />

            <br/>

            <asp:label id="Message" runat="server"/>    

            <asp:hiddenfield id="ValueHiddenField"
              onvaluechanged="ValueHiddenField_ValueChanged"
              value="" 
              runat="server"/>

        </form>
    </body>
</html>

<script type="text/javascript">

  <!--
  function PageLoad()
  {

    // Set the value of the HiddenField control with the
    // value from the TextBox.
    Form1.ValueHiddenField.value = Form1.ValueTextBox.value;

  }
  -->

</script>

.NET Framework Security

AspNetHostingPermission
for operating in a hosted environment. Demand value: LinkDemand. Permission value: Minimal.
AspNetHostingPermission
for operating in a hosted environment. Demand value: InheritanceDemand. Permission value: Minimal.

Inheritance Hierarchy

System..::.Object
System.Web.UI..::.Control
System.Web.UI.WebControls..::.HiddenField

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0

Reference

HiddenField Members

System.Web.UI.WebControls Namespace

System.Web.UI.HtmlControls..::.HtmlInputHidden

Value

ValueChanged