Extend ASP.NET AJAX Client-Side Function - The Server-Side Way
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by Xianzhong Zhu
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The WebControl Way

Extenders are great for providing client functionality to existing server controls in an incremental way. In many cases, however, we do not want or do not need an external control to wire client components to a server control. To describe both the server-side and the client-side functionalities in a single place, we can resort to script controls. In fact, Script controls are ASP.NET server controls that can provide script references and script descriptors without relying on an external object.

Generally, if we are writing the control from scratch, we can safely derive from the base ScriptControl class, which takes care of registering the script control with the ScriptManager under the hood. The only difference between coding the control and coding an extender is that the properties used to configure the client component and the overrides of the methods defined in the IScriptControl interface are embedded in the control rather than in a different object.

In some cases we may want to convert an existing control into a script control. In such a case we have to derive a class from the existing server control and manually implement interface IScriptControl.

The following sections will introduce to you the IScriptControl interface.

The IScriptControl Interface and Registering the Script Control

The IScriptControl interface defines two methods; Listing 8 and the following Table 3 describe their respective functionalities:

Listing 8

public interface IScriptControl
{
  IEnumerable<ScriptDescriptor> GetScriptDescriptors();
  IEnumerable<ScriptReference> GetScriptReferences();
}

Table 3

Method

Description

GetScriptDescriptors

Gets a collection of script descriptors that represent JavaScript components on the client. This method is used to map server-side control properties to client-side control properties.

GetScriptReferences

Gets a collection of ScriptReference objects that define script resources required by the control. This method is used to identify one or more embedded script resources in a control assembly and output them to the client.

Registration with the ScriptManager is necessary in order to recognize a script control as an Ajax-enabled control.  It is a two-step process similar to that used for extenders.

1. During the PreRender stage, we call the RegisterScriptControl method, passing the script control instance as an argument.

2. During the Render stage, you call the RegisterScriptDescriptors method to register the script descriptors.

Here we are unwilling to chatter too much about the pure theories. Thus, let us make room for a simple sample to let it tell every detail.


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