Welcome!

Machine Learning Authors: Pat Romanski, Liz McMillan, Yeshim Deniz, Elizabeth White, Zakia Bouachraoui

Related Topics: Machine Learning , Microsoft Cloud

Machine Learning : Article

Google Maps! AJAX-Style Web Development Using ASP.NET

Taking asynchronous Web forms to the next level

In the past few months, the design pattern of combining Asynchronous JavaScript and XML (AJAX) to develop highly interactive Web applications has been growing in popularity. High-profile Web applications such as Google Maps and A9 are currently leveraging the combination of these technologies to produce rich client-side user experiences. The individual technologies that compose AJAX are not recent developments; they have been around for some time and have been continuously updated and improved. However, it is the recent confluence of these technologies that is leading to interesting possibilities.

I have three goals in this article. First, I want to provide a high-level overview of AJAX-style applications. My second goal is to provide a detailed description of asynchronous callback features of ASP.NET 2.0. Finally, I want to provide an insight into upcoming enhancements of tools and frameworks for building AJAX-style applications.

AJAX-style Web applications exhibit the following characteristics:

  • Asynchronous requests made to the Web server. The browser user interface is not blocked while waiting for a response from the Web server. The browser can continue to respond to user interaction while awaiting a server response.
  • High dependence on browser-based logic written in JavaScript. Recent enhancements to and standardization of the W3C DOM provide support for dynamic client-side updates to UI.
  • Exchange of nonpresentation XML-based data between the browser and the Web server. The XMLHttp object makes it possible to communicate with the Web server without the need to reload the page.
The big difference between an AJAX application and a traditional Web application is that every user interaction does not result in an HTTP request being sent to the Web server. Instead, browser-based logic implemented in JavaScript receives control that, in turn, decides whether to handle the request locally or to make an asynchronous call to the server. Upon the completion of the asynchronous call to the server, the client-side logic appropriately updates the relevant sections of the UI. This approach provides the following benefits:
  • The user experience is richer. For example, when a Google map user drags the map in one direction, an asynchronous request is made to the server in the background, to continue to fetch tiles beyond the edge of the screen. This way when the user drags the map further, the new image is readily available. This creates a perception of a speedier response.
  • Since the state is not lost across XMLHttp-based calls to the server, AJAX applications can avoid rerendering the UI widgets each time.
  • More logic residing in the browser reduces the number of roundtrips to the Web server, thereby improving the overall latency of the system.
For all the pros, AJAX-style applications have a number of cons associated with them as well. AJAX-style development is difficult because of the absence of framework (a collection of UI classes similar to the MFC toolkit for Windows) and IDE support (i.e., debugging, visual designers, etc.). One has to know at least two languages well (DHTML and JavaScript). Further, AJAX-style applications take longer to code because of the additional testing required to support multiple browser versions and types. Finally, as the JavaScript-based source is accessible to the end user, threat analysis becomes very important.

Fortunately, the arrival of things such as Atlas, AJAX.NET, and the Google Maps API etc. is a sign of better support for building AJAX-style applications in the future. In the next section, we will look into how the support for building AJAX applications is evolving over time and what to expect from the newly announced toolkits such as Atlas.

Let's start with the XMLHttp object, which was introduced by Microsoft and later implemented on other platforms including Mozilla and Apple's Safari browser. XMLHttp enables asynchronous requests to the Web server, which allows Javascript- based logic on the client to call the Web server without the need to reload the page.

In other words, it is possible to have interaction with the Web server in the background without causing a page reload - a side effect of the exchange between the browser and the Web server.

Using the XMLHttp object is straightforward. For the sake of simplicity, let's just consider IE specific syntax. The syntax for XMLHttp implementations on other browsers is similar.


request = new ActiveXObject("Microsoft.XMLHTTP");
if (request)
{
request.onreadystatechange = CallbackHandler;
request.open("GET", URL, true);
request.send();
}

function CallbackHandler()
{
if ((request.readyState == 4) && (request.status == 200)
{
string response = request.responseXML;

// Update the relevant sections of the UI

}
}
In the code snippet shown above, the first step is to instantiate the Microsoft.XMLHttp class. Next, we set the properties on the XMLHttp instance we just created, including the address of callback function that will get control when the XMLHttp request is complete. The callback function address is needed because we are making asynchronous calls to the server (an intent conveyed by setting the third parameter on the open method call to true). Inside the implementation for the callback function, we make additional checks to make sure that the request is complete.

More Stories By Vishwas Lele

Vishwas Lele is a principal architect at Applied Information Sciences (www.appliedis.com), a system and software engineering company specializing in .NET-based solutions. Vishwas also serves as the MSDN Regional Director for the Washington, DC area.

Comments (17)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


CloudEXPO Stories
Every organization is facing their own Digital Transformation as they attempt to stay ahead of the competition, or worse, just keep up. Each new opportunity, whether embracing machine learning, IoT, or a cloud migration, seems to bring new development, deployment, and management models. The results are more diverse and federated computing models than any time in our history.
On-premise or off, you have powerful tools available to maximize the value of your infrastructure and you demand more visibility and operational control. Fortunately, data center management tools keep a vigil on memory contestation, power, thermal consumption, server health, and utilization, allowing better control no matter your cloud's shape. In this session, learn how Intel software tools enable real-time monitoring and precise management to lower operational costs and optimize infrastructure for today even as you're forecasting for tomorrow.
"Calligo is a cloud service provider with data privacy at the heart of what we do. We are a typical Infrastructure as a Service cloud provider but it's been designed around data privacy," explained Julian Box, CEO and co-founder of Calligo, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Isomorphic Software is the global leader in high-end, web-based business applications. We develop, market, and support the SmartClient & Smart GWT HTML5/Ajax platform, combining the productivity and performance of traditional desktop software with the simplicity and reach of the open web. With staff in 10 timezones, Isomorphic provides a global network of services related to our technology, with offerings ranging from turnkey application development to SLA-backed enterprise support. Leading global enterprises use Isomorphic technology to reduce costs and improve productivity, developing & deploying sophisticated business applications with unprecedented ease and simplicity.
While a hybrid cloud can ease that transition, designing and deploy that hybrid cloud still offers challenges for organizations concerned about lack of available cloud skillsets within their organization. Managed service providers offer a unique opportunity to fill those gaps and get organizations of all sizes on a hybrid cloud that meets their comfort level, while delivering enhanced benefits for cost, efficiency, agility, mobility, and elasticity.