Introduction:
In this article,i am going explain about how to build a asynchronous webpages using async attribute in asp.net 2.0
and above versions.

Main:
The Isasync attribute helps you to create asynchronous webpages,

The new Async attribute on the @Page directive accepts a Boolean value to enable or disable asynchronous processing. The default value is false.

<%@ Page Async="true" ... %>

The AddOnPreRenderCompleteAsync Method

The AddOnPreRenderCompleteAsync method adds an asynchronous event handler for the page’s PreRenderComplete event. An asynchronous event handler consists of a Begin/End pair of event handler methods, as shown here:

AddOnPreRenderCompleteAsync (
newBeginEventHandler(BeginTask),
newEndEventHandler(EndTask)
);

The BeginEventHandler and EndEventHandler are delegates defined as follows:

IAsyncResult BeginEventHandler( object sender, EventArgs e, AsyncCallback cb, object state) void EndEventHandler( IAsyncResult ar)

See this below simple program examble,I am created one webpage and fetching my rss feeds asynchronously,

For downloading this sample code click here

Conclusion:
Hope this helps,
happy Coding.