I've been using the ASP.NET AJAX Update Panels for quite some time now and have picked up a lot of tips on when and how to use them. Update Panels were intended to allow the developer to do Partial Page Updates. Usually what you see is Update Panels updating nearly the entire page which completely defeats the purpose of Update Panels!

Here are some good tips to take into account when developing with Update Panels:

#1. One thing I notice is that people want to stuff all their functionality into one page with multiple hidden/visible panels. Then utilize the functionality by showing/hiding the panels based on actions within the page. This can lead to very confusing code...

If you're changing from one action which does a lot of functionality with X to an action which does a lot of functionality with Y then separate the functionality and use a page postback to switch between those pages. Don't throw everything together into one update panel and separate it by hidden panels. You'll end up with a ton of code which is not resuable and difficult to understand. Separate your functionality just like you would separate your DAL, BL and Presentation.

• User Management (insert, update, delete users)
• Settings (change your web app's settings)
• Media Management (insert, update, delete media)
• etc...

#2. Separate your Update Panels. Instead of throwing everything into one update panel break it up! Plan what areas of your page will need to update and what will trigger them to update. This will save you an insane amount of bandwidth (and download time) and return much better performance.

Example:
Lets say you have 3 areas on your page that will allow a user to: select a category, select a video and then watch the video.

• Part 1 displays a list of categories
• Part 2 displays a list of videos within that category
• Part 3 displays a video player

Lets think logically about the flow of execution with the 3 parts. First a user picks a category in Part 1. Then they select which video they want to watch in Part 2. And finally the video displays in Part 3 and begins playing.

So there are 2 steps involved to watch a video:

1. Pick a category
2. Pick a video

And 2 triggers:

1. "Click" a category
2. "Click" a video

(Each arrow represents a click)

So we've got the basic idea down now how do we determine WHERE we need update panels? We need to determine what parts change. The only parts that change are Part 2 which shows a list of videos within the selected category and Part 3 which plays the selected video. Part 1 will not change because nothing within that part changes. Part 1 is only used to select a category and the categories are loaded at Page_Load.

(Of course if you added paging or sorting to Part 1 you could then use an update panel but for this example Categories are static.)

So you have 2 parts that change meaning you only need 2 update panels, one for Part 2 and one for Part 3. Now how do we trigger these updates? Based on the flow we determined above we know what triggers are needed...

Triggers:

• Part 2 needs to update when a category is selected from Part 1.
• Part 3 should update when a video is selected from Part 2.

We also want to hide the video player when the user selects a new category because it wouldn't make sense to continue showing a video from the "Comedy" category after they selected the "Drama" category. So we'll need one more trigger:

• Part 3 should update when a category has been selected since we don't want to display the old video when they select a new category.

(Each arrow represents where the item is triggered from [start of line inside part] and what part it affects [end of line])

And that's all we need to properly separate our update panels. The cool thing about upate panels is that your trigger control does not need to be within the same update panel. In other words, it can be located anywhere on your page outside the update panel. That's why we only need 2 update panels. The triggers in part 1 can be set programatically or through the update panel "triggers" GUI from the properties menu.

Quick Tip: If you want to know how to set a trigger programatically then read this post.

What's the benefit of separating the update panels? Alot of Bandwidth! Update panels respond with their entire rendered contents when doing an AJAX call. Update panels also attach any control viewstates to the response. If you were to place the entire content of the example above in one update panel you'll be uploading and downloading everything every time you do a callback. On the other hand if you separate your update panels, like the example above, you'll only download the contents of the update panel that has been triggered.

Quick Tip: If a control within an update panel does not need viewstate enabled then disable it! This is a good way to decrease the size of the response.