Working with Atlas' ScriptManager class
Wednesday, May 17, 2006 10:41 AM
Last week we surveyed Microsoft's answer to the AJAX buzz in the form of Atlas. Basically, Atlas is an ASP.NET 2.0 framework for building cross-browser, cross-platform AJAX applications.
Microsoft recently released the April Community Technology Preview and stated that it feels it is ready for a go live license. With that in mind, this week we'll examine the centerpiece of Atlas: the ScriptManager class.
The center of attention
The ScriptManager class manages
all Atlas components on a Web page. In addition, it handles partial page
updates, and renders client scripts that enable you to access Web service
methods from JavaScript using proxy objects.
Every page that utilizes Atlas components must contain only one ScriptManager control, which is declared in the head portion of a Web page. It registers the Atlas scripts, making them available on the page. If you're using ASP.NET 2.0, then you can include a ScriptManager control on a master page, thus making it available to all pages that use that master page. The ScriptManager control uses the syntax in Listing A.
Let's take a closer look at various aspects of declaring a ScriptManager control:
- EnablePartialRendering: This attribute signals whether partial rendering is enabled. Partial rendering is used to reload only portions or sections of a page. If true, regular postbacks from asynchronous controls are present with only incremental changes sent to the client.
- EnableScriptComponents: This attribute controls which parts of Atlas are available on the client by default. It determines whether Atlas scripts for user-interface components, behaviors, databinding, and XML scripting are downloaded to the client by default. If false, you can download specific components in the ScriptReference element.
- ScriptReference: This element (which must be enclosed in a Scripts element) allows you to add scripts that are not included automatically. Scripts are designated with the Path attribute, and you may specify a browser for that script with the Browser attribute. Atlas does include some scripts that are not sent to the client by default; these may be included with the ScriptName attribute. These scripts include AtlasUIDragDrop, AtlasUIGlitz, and AtlasUIMap.
- ServiceReference: This element allows you to designate Web services that may be used in scripts on the page. The Type attribute can be any valid MIME type. The GenerateProxy attribute allows you to temporarily disable the generation of proxy objects for services listed in the Scripts collection.
The Web page in Listing B utilizes a local Web service (although it could be any service). The page declares the Web service reference that is later used in JavaScript to utilize its sole method. Partial page rendering is disabled, as well as the loading of all script libraries. The ScriptReference section references the AtlasRuntime script library (installed with Atlas), so basic functionality is available. The source code for the service is in Listing C.
Using more than one ScriptManager control
While you are restricted to one instance of a ScriptManager control on a Web page, you may want to add
additional script or service references to a page. In this scenario, the ScriptManagerProxy control is provided.
<atlas:ScriptManagerProxyrunat="server"
id="smProxy">
...
</atlas:ScriptManagerProxy>
This control may be useful if you need to utilize additional scripts (ScriptReference element) when a ScriptManager object has already been declared. A good example involves ASP.NET 2.0 and placing a ScriptManager object on a master page. Pages that utilize the master page may need to utilize additional scripts, so the proxy object is available. It uses the same syntax as the regular ScriptManager control.
Other controls
While the ScriptManager control is
the focal point of Atlas-based Web pages, the framework includes a few controls
out-of-the-box to enhance a Web page with little programming. Here is an
overview of the controls included with the most recent edition of Atlas:
- AutoCompleteExtender: Allows you to extend text box controls to provide auto-completion behavior. A Web service is used to provide the suggestion data.
- DragOverlayExtender: You can turn a server control into a floating control that may be moved with the mouse/keyboard.
- ProfileScriptService: Creates a client-side profile component for access to ASP.NET user profiles.
- TimerControl: Creates a client-side timer that performs a postback at regular intervals.
There are many examples on the Atlas Web site, but the DragOverlayExtender control is one of the coolest and easiest to implement. Basically, you create a control and assign it to an instance of the DragOverlayExtender control's TargetControlID property to get it working. The example in Listing D demonstrates its use by allowing an image to be moved around the page.
Additional info
System administrators are unnecessary to work with
Atlas--you can simply copy the Microsoft.Web.Atlas.dll file into your projects'
\bin directory and copy the Atlas \ScriptLibrary
directory of .js files into your project and
everything is ready to go.
Also, while Atlas does have the Microsoft label, it was designed to be browser agnostic. All styling for Atlas-based controls is accomplished with CSS. In addition, Atlas allows you to develop browser-specific content if necessary.
Finally, some argue that Atlas is simply a ploy to steer developers away from Firefox and Opera, which continue to gain market share in the browser space. While I'm sure Microsoft is aware of its competitors' actions, I don't worry too much about the software giant's motives; I just want technology that allows me to build powerful solutions for my clients. Atlas may (or may not) fill that need when it is finally release, but I like what I see to date.
Starting point
While the Atlas framework has not been officially released
as a product, the latest technology preview gives you an idea of what to
expect. You should understand that Atlas simplifies AJAX development with the ScriptManager control at its nucleus. Everything you do
with Atlas will utilize this control, so you should be familiar with its usage
and options when working with Atlas-based solutions.
Tony Patton began his professional career as an application developer earning Java, VB, Lotus, and XML certifications to bolster his knowledge.
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