Page 65 - DCAP312_WEB_TECHNOLOGIES_II

Unit 4: Advanced Server Controls

expect other web sites to perform with the same elegance as they do. When a web site does Notes
not perform with the same elegance the user will often move onto another web site that does.
Those popular applications have raised the bar for what is an acceptably user-friendly web site.
Because our users are demanding a web site experience that essentially uses Ajax and we build
our ASP.NET web sites using server controls, we need a way of easily creating server controls
that not only encapsulate browser appearance and server functionality, but also include Ajax
functionality so that the server control itself is Ajax-enabled.
Taking a step back for a moment, unlike other technologies we might have read books on, ASP.
NET AJAX server controls do not provide we with anything that we could not already do. We
have always been able to embed Ajax-functionality into server controls it was just a real pain.
There were a few different methods we could use to include the JavaScript with our server
control such as embedding it as a resource, but we eventually ended up having to do the same
three tasks. To make our server control have some serious client capabilities we always had to
concatenate strings together to form JavaScript statements and functions, write browser sniffing
statements to make sure that the JavaScript was cross-browser compatible, and add attributes
or render out Html that attached the JavaScript functionality to the client versions of our server
controls. It was not impossible, but it was error-prone and there was always this mingling of
server code and JavaScript that was hard to maintain and even harder to read.
Furthermore, if we had multiple server controls that had client capabilities it was difficult (but
not impossible) to ensure that the client functions that each server control required did not
overwrite each other when rendered on the browser. Tracking down that problem was always
a fun hour or so. The difficulty grew exponentially if we wanted to include a mechanism for
asynchronously communicating with the server when the user pressed a button embedded in the
server control. Even with a helper communication library there were always tricks to getting our
control to communicate properly with the server. These hindrances were problematic enough to
lead to some bad programming habits and bad code as well as scare programmers away from
even attempting to include Ajax-functionality in their server controls. These problems are what
Microsoft’s ASP.NET AJAX solves.

4.1 HTML Server Controls

The HTML server controls are basically the inventive HTML controls but improved to enable
server side processing. The HTML controls like the subtitle tags, anchor tags and contribution
elements are not processed by the server but sent to the browser for show.
They are specifically converted to a server control by adding the attribute runat= “server” and
adding an id attribute to make them available for server-side processing.
For example, consider the HTML input control:
<input type= “text” size= “40”>
It could be converted to a server control, by adding the runat and id attribute:
<input type= “text” id= “testtext” size= “40” runat= “server”>

4.1.1 Advantages of Using HTML Server Controls
Though ASP.Net server controls can execute every job accomplished by the HTML server
controls, the later controls are useful in the following cases:
• Using static tables for layout purposes.
• Converting a HTML page to run under ASP.NET.

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