What is Use of Scriptmanager in asp.net AJAX

The ScriptManager control manages client script for Microsoft ASP.NET AJAX pages. By default, the ScriptManager control registers the script for the Microsoft AJAX Library with the page. This enables client script to use the type system extensions and to support features such as partial-page rendering and Web-service calls.

Background
When a page contains one or more UpdatePanel controls, the ScriptManager control manages partial-page rendering in the browser. The control interacts with the page life cycle to update the parts of the page that are inside UpdatePanel controls. For more information, see Partial-Page Rendering Overview.

The EnablePartialRendering property of the ScriptManager control determines whether a page participates in partial-page updates.


ScriptManager is a server-side control that sits on your Web Form and enables the core of ASP.NET AJAX. Its primary role is the arbitration of all other ASP.NET AJAX controls on the Web Form and the addition of the right scripting libraries to the Web browser so that the client portion of ASP.NET AJAX can function. Often you will find yourself using the ScriptManager to register other controls, Web services, and client scripts.
As a server-side control, ScriptManager reacts to events in the ASP.NET page lifecycle and uses those events to coordinate the activities of all the controls, options, and code employed by ASP.NET AJAX. ScriptManager will hook a particular event, get notified when it occurs, and configure a few settings depending on the environment; this process will repeat itself several times through the rendering cycle of your ASP.NET page. The settings it configures, however, are often the exact settings needed to make your use of ASP.NET AJAX seamless.

Why Use the ScriptManager Control

You must use a ScriptManager control on a page to enable the following features of ASP.NET AJAX:

Client-script functionality of the Microsoft AJAX Library, and any custom script that you want to send to the browser. For more information, see ASP.NET AJAX and JavaScript.

Partial-page rendering, which enables regions on the page to be independently refreshed without a postback. The ASP.NET AJAX UpdatePanel, UpdateProgress, and Timer controls require a ScriptManager control to support partial-page rendering.

JavaScript proxy classes for Web services, which enable you to use client script to access Web services by exposing Web services as strongly typed objects.

JavaScript classes to access ASP.NET authentication and profile application services.

Enabling Partial-Page Rendering

When a page contains one or more UpdatePanel controls, the ScriptManager control manages partial-page rendering in the browser. The control interacts with the page life cycle to update the parts of the page that are inside UpdatePanel controls. For more information, see Partial-Page Rendering Overview.

The EnablePartialRendering property of the ScriptManager control determines whether a page participates in partial-page updates. By default, the EnablePartialRendering property is true. Therefore, partial-page rendering is enabled by default when you add a ScriptManager control to the page. For information about how to use the UpdatePanel control with the ScriptManager control, see Introduction to the UpdatePanel Control and Creating a Simple ASP.NET Page with Multiple UpdatePanel Controls.

Handling Errors

During partial-page rendering, you can handle errors by doing the following:

Set the AllowCustomErrorsRedirect property, which determines how the custom error section of the Web.config file is used when an error occurs during an asynchronous postback.

Handle the ScriptManager control's AsyncPostBackError event, which is raised when there is a page error during an asynchronous postback.

Set the AsyncPostBackErrorMessage property, which is the error message that is sent to the browser.

Using Type System Extensions

Microsoft AJAX Library adds type-system extensions to JavaScript that provide namespaces, inheritance, interfaces, enumerations, reflection, and helper functions for strings and arrays. These extensions provide functionality in client script that is like that of the .NET Framework. They enable you to write ASP.NET 2.0 AJAX Extensions applications in a structured way that improves maintainability, makes it easier to add features, and makes it easier to layer functionality. Adding a ScriptManager control to an ASP.NET Web page automatically includes the type-system extensions so that you can use the library in client script.

Registering Custom Script

Use the ScriptManager control to manage resources that you have created for controls that participate in partial-page updates. Resources include scripts, styles, hidden fields, and arrays. The Scripts collection of the ScriptManager control contains a ScriptReference object for each script that is available to the browser. You can specify the scripts declaratively or programmatically.

The ScriptManager control also exposes registration methods that you can use to manage client script and hidden fields programmatically. When you are registering script or hidden fields that support partial-page updates, you must call registration methods of the ScriptManager control. (To register scripts that are not needed for partial-page updates, you use methods of the ClientScriptManager class.)


Registering Web Services

The ScriptManager control's Services collection contains a ServiceReference object for each Web service that is registered with the ScriptManager control. The ASP.NET AJAX framework generates a client proxy object for each ServiceReference object in the Services collection. The proxy classes and their strongly typed members simplify using Web services from client script.
You can programmatically add ServiceReference objects to the Services collection to register Web services at run time.

Using Authentication and Profile Services from Client Script

The Microsoft AJAX Library includes proxy classes for calling the ASP.NET 2.0 forms authentication and profile application services directly from JavaScript. If you want to use a custom authentication service, you can register it using the ScriptManager control.

The ScriptManagerProxy Class

Only one instance of the ScriptManager control can be added to the page. The page can include the control directly, or indirectly inside a nested component such as a user control, content page for a master page, or nested master page. In cases where a ScriptManager control is already on the page but a nested or parent component needs additional features of the ScriptManager control, the component can include a ScriptManagerProxy control. For example, the ScriptManagerProxy control enables you to add scripts and services that are specific to nested components.