Are MS UpdatePanels Really Not AJAX?

Question

I keep hearing that ASP.NET AJAX elements on the server side (like UpdatePanels) are not really AJAX, although they seem to them because the rendering is not entirely client-side. I try to understand this with greater clarity. Can someone clarify?

Thanks...

Answer 1

UpdatePanels came out quite early in the AJAX cycle, and they are heavy (they can emit about 100-300 thousand JavaScript). Behind the scenes, UpdatePanels sends the entire page back to the server using XMLHttpRequest. A new page is created with the usual page life cycle, as for postback, but only the parts that live inside the UpdatePanel (plus the parts needed to update the ViewState, etc.) are sent back to the client. From there, the markup is inserted without a visible flash or interruption of the page state.

Most competing AJAX tools focus on ultra-lightweight implementations that let you send or generate a small piece of HTML through Javascript, and I would say that this is the dominant trend today, especially outside the ASP.NET world.

The difference in the total amount of data transmitted over the wires is huge - see the link below. In low traffic situations, this may not matter much, but in the case of a site like StackOverflow, it will most likely be displayed on the bandwidth account.

All that said, I don't think it's fair to say that UpdatePanels are not really AJAX, since they send HTML via asynchronous JavaScript - it's just a giant, often cumbersome structure on top. UpdatePanels sometimes get bad rap, but they provide a brilliantly simple developer experience. I often found them useful in low traffic situations.

Update: Here is an article (old, but still valid) that checks UpdatePanels download packages from the server as well. It also goes into "Page Methods," which is a lightweight alternative to Web Services-based UpdatePanels. This is a frequently forgotten part of Microsoft AJAX.

Answer 2

http://msdn.microsoft.com/en-us/magazine/cc163480.aspx

Maybe this will answer?

I hope so. (Reading also).

It seems to me that the control is a server-side object that uses ajax as a mechanism and that ajax is rendered on the client side. In this sense, this is not a pure ajax, but rather a mixture of several solutions.

:)