C# 4 and .NET 4

1228 ❘ ChaPTer 41 Asp.net feAtures
The scriptManager Control
As mentioned earlier in the chapter, the ScriptManager control must be included on all pages that use
partial - page postbacks and several other aspects of ASP.NET AJAX functionality.
A great way to ensure that all the pages in your web application contain the
ScriptManager control is to add this control to the master page (or master pages) that
your application uses.
As well as enabling ASP.NET AJAX functionality, you can also use properties to confi gure this control. The
simplest of these properties is EnablePartialRendering , which is true by default. If you set this property
to false , you will disable all asynchronous postback processing, such as that provided by UpdatePanel
controls. This can be useful, for example, if you want to compare your AJAX - enabled web site with a
traditional web site; perhaps if you are giving a demonstration to a manager.
You can use the ScriptManager control for several reasons, such as in the following common situations:
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To determine whether server - side code is being called as a result of a partial - page postback
To add references to additional client - side JavaScript fi les
To reference Web services
To return error messages to the client
These confi guration options are covered in the following sections.
Detect Partial - Page Postbacks
The ScriptManager control includes a Boolean property called IsInAsyncPostBack . You can use
this property in server - side code to detect whether a partial - page postback is in progress. Note that the
ScriptManager for a page may actually be on a master page. Rather than accessing this control through
the master page, you can obtain a reference to the current ScriptManager instance by using the static
GetCurrent() method, for example:
ScriptManager scriptManager = ScriptManager.GetCurrent(this);
if (scriptManager != null & & scriptManager.IsInAsyncPostBack)
{
// Code to execute for partial - page postbacks.
}
You must pass a reference to a Page control to the GetCurrent() method. For example, if you use this
method in a Page_Load() event handler for an ASP.NET web page, you can use this as your Page
reference. Also, remember to check for a null reference to avoid exceptions.
Client - Side JavaScript References
Rather than adding code to the HTML page header, or in elements on the page, you can use the
Scripts property of the ScriptManager class. This centralizes your script references and makes it easier to
maintain them. You can do this declaratively by adding a child element to the
control element, and then adding child control elements to . You use
the Path property of a ScriptReference control to reference a custom script.
The following sample shows how to add references to a custom script fi le called MyScript.js in the root
folder of the web application:
< asp:ScriptManager runat="server" ID="ScriptManager1" >
< Scripts >
< asp:ScriptReference Path="~/MyScript.js" / >
< /Scripts >
< /asp:ScriptManager >
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