Since ASP.NET AJAX
UpdatePanel was first introduced, it has earned a strange mix of reputation. On the one hand, it has become a tool of first choice for many ASP.NET developers who wanted an easy way of introducing an AJAX-like behavior for their ASP.NET web apps. On the other hand, it has earned a lot of criticism from seasoned web developers because of certain performance consequences associated with complex usage scenarios.
Well, everything may be good and may be evil based on how we use it. From my experience, conscious and judicious use of
UpdatePanel is the key to saving its benefits and avoiding potential problems.
Below, I suggest a number of rules that help achieving better results when using
- Avoid automatic refreshing of
UpdatePanel; always stay in control of which
UpdatePanel and when refreshes: set
UpdateMode property to
Conditional (the default value is
- Minimize the content of the
<ContentTemplate> should only include controls that are necessary to refresh. For instance, if user input requires server-side validation, include only an error message mark-up in the
UpdatePanel and leave the rest of the form outside.
- Try to keep the partial postback trigger controls outside of their respective
UpdatePanels unless its necessary to change their markup.
- Try to stick to a simple rule: one trigger for one
UpdatePanel. If you need to refresh multiple
UpdatePanels during one request, add a trigger control to only one of those
UpdatePanels and refresh the others programmatically in an event handler on the server. The idea is to avoid uncontrollable refreshing of unnecessary
ViewState is updated with every partial postback request, turn the
ViewState off on a page that contains the
UpdatePanel wherever possible or store the
ViewState on the server to avoid transferring it back and forth with every async request.
- Since Page runs through its lifecycle during every partial postback and executes methods like
Page_PreRender, make sure that logic that is unnecessary for refreshing
UpdatePanel is not executed by wrapping it in
- If you use
UpdatePanel event handlers like
Unload, make sure that code inside these event handlers does not execute unless necessary by checking
- If you trigger an
Request.Params["__EVENTTARGET"] to avoid unnecessary execution path.
- If you programmatically update Page's Header (Title, etc.) or other Page's content that is outside
UpdatePanel, make sure that this code never gets executed during partial postbacks. First of all, it's not necessary since page does not refresh but also it may be dangerous because the content may not be handled properly by a browser.
There may probably be more tricks and tips regarding usage of
UpdatePanel, but those mentioned above have been proven by real experience. I would also recommend reading an excellent post by Dave Ward that helps in understanding how
UpdatePanel works behind the scenes and never hesitate using Fiddler to investigate what your web app's doing.
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