Substitution Constructor ()

 

Initializes a new instance of the Substitution class.

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

Public Sub New

Use the Substitution constructor to create and initialize a new instance of the Substitution class.

The following code example demonstrates how to add a Substitution control programmatically to an output-cached Web page. When the page loads, the current date and time are displayed to the user in a label. This section of the page is cached and updated only every 60 seconds. When the Substitution control executes, it calls the GetCurrentDateTime method. The string returned by GetCurrentDateTime is displayed to the user. This section of the page is not cached and is updated each time the page is refreshed.

<%@ outputcache duration="60" varybyparam="none" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server" language="VB">  

  Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
    ' Programmatically create a Substitution control.
    Dim Substitution1 As New Substitution

    ' Specify the callback method.
    Substitution1.MethodName = "GetCurrentDateTime"

    ' Add the Substitution control to the controls
    ' collection of PlaceHolder1.
    PlaceHolder1.Controls.Add(Substitution1)

    ' Display the current date and time in the label.
    ' Output caching applies to this section of the page.
    CachedDateLabel.Text = DateTime.Now.ToString()
  End Sub

  ' The Substitution control calls this method to retrieve
  ' the current date and time. This section of the page
  ' is exempt from output caching. 
  Shared Function GetCurrentDateTime(ByVal context As HttpContext) As String
    Return DateTime.Now.ToString()
  End Function

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
  <title>Substitution Constructor Example</title>
</head>
<body>
  <form id="Form1" runat="server">

    <h3>Substitution Constructor Example</h3>  

    <p>This section of the page is not cached:</p>
    <asp:placeholder id="PlaceHolder1"
      runat="Server">
    </asp:placeholder>

    <br />

    <p>This section of the page is cached:</p>

    <asp:label id="CachedDateLabel"
      runat="Server">
    </asp:label>

    <br /><br />

    <asp:button id="RefreshButton"
      text="Refresh Page"
      runat="Server">
    </asp:button>     

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

.NET Framework
Available since 2.0
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