ClientScriptManager.IsClientScriptBlockRegistered Method (Type, String)

 

Determines whether the client script block is registered with the Page object using a key and type.

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

Public Function IsClientScriptBlockRegistered (
	type As Type,
	key As String
) As Boolean

Parameters

type
Type: System.Type

The type of the client script block to search for.

key
Type: System.String

The key of the client script block to search for.

Return Value

Type: System.Boolean

true if the client script block is registered; otherwise, false.

Exception Condition
ArgumentNullException

The client script type is null.

Call this method before calling the RegisterClientScriptBlock method to avoid registering duplicate scripts. This is particularly important if the script requires a large amount of server resources to create.

A client script is uniquely identified by its key and its type. Scripts with the same key and type are considered duplicates. You specify the type based on the object that will be accessing the resource. For instance, when using a Page instance to access the resource, you specify the Page type.

The following code example demonstrates the use of the IsClientScriptBlockRegistered method. Note that, if the logic to check for the existing client script block were removed, there would not be two duplicate client scripts in the HTML source code of the rendered page because the RegisterClientScriptBlock method checks for duplicates. The benefit of checking is to reduce unnecessary computation.

<%@ 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">

  Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)

    ' Define the name and type of the client scripts on the page.
    Dim csname1 As String = "PopupScript"
    Dim csname2 As String = "ButtonClickScript"
    Dim cstype As Type = Me.GetType()

    ' Get a ClientScriptManager reference from the Page class.
    Dim cs As ClientScriptManager = Page.ClientScript

    ' Check to see if the startup script is already registered.
    If (Not cs.IsStartupScriptRegistered(cstype, csname1)) Then

      Dim cstext1 As String = "alert('Hello World');"
      cs.RegisterStartupScript(cstype, csname1, cstext1, True)

    End If

    ' Check to see if the client script is already registered.
    If (Not cs.IsClientScriptBlockRegistered(cstype, csname2)) Then

      Dim cstext2 As New StringBuilder()
            cstext2.Append("<script type=""text/javascript""> function DoClick() {")
      cstext2.Append("Form1.Message.value='Text from client script.'} </")
      cstext2.Append("script>")
      cs.RegisterClientScriptBlock(cstype, csname2, cstext2.ToString(), False)

    End If

  End Sub

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>ClientScriptManager Example</title>
  </head>
  <body>
     <form id="Form1"
         runat="server">
        <input type="text" id="Message" /> <input type="button" value="ClickMe" onclick="DoClick()" />
     </form>
  </body>
</html>

.NET Framework
Available since 2.0
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