HiddenField Class (System.Web.UI.WebControls)

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Microsoft Visual Studio 2005/.NET Framework 2.0

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.NET Framework Class Library

HiddenField Class

Note: This class is new in the .NET Framework version 2.0.

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")> _
Public Class HiddenField
    Inherits Control
    Implements IPostBackDataHandler

Visual Basic (Usage)

Dim instance As HiddenField

[ControlValuePropertyAttribute("Value")] 
public class HiddenField : Control, IPostBackDataHandler

C++

[ControlValuePropertyAttribute(L"Value")] 
public ref class HiddenField : public Control, IPostBackDataHandler

/** @attribute ControlValuePropertyAttribute("Value") */ 
public class HiddenField extends Control implements IPostBackDataHandler

JScript

ControlValuePropertyAttribute("Value") 
public class HiddenField extends Control implements IPostBackDataHandler

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.

Example

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

Visual Basic

<%@ Page language="VB" %>

<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>
    <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 language="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#" %>

<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>
    <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 language="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 98, Windows 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

Version Information

.NET Framework

Supported in: 2.0

Reference

HiddenField Members
System.Web.UI.WebControls Namespace
System.Web.UI.HtmlControls.HtmlInputHidden
Value
ValueChanged

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