Demo 1 (Enter a few numbers in the search field and see how many items are being filtered and how long it takes.)
Source 1

Notice that in order to keep track of how many items are reaching the main part of the filter I increment a Bindable variable inside the filter function:

[Bindable] private var ffCount:Number = 0;
...
private function ff(item:Object):Boolean
{
...
    ffCount++;
...
}

Now since I’ve been programming in Flex for over four years you’d think I’d know better. Every time a Bindable object is modified Flex does a bunch of event dispatching and other plumbing. In this case the Label which is bound to the ffCount variable is also doing a bunch of work each time ffCount changes. As you can see, the results are not great. It takes almost a full second (on my machine) to do the filter on 20,000 items. Obviously this isn’t right.

Lesson learned: A Flex application should never, ever, ever, update Bindable objects in filter functions or other places where the user won’t ever be able to distinguish something changing that rapidly.

A better approach is to update a non-Bindable variable in the loop or filter function, then when the loop or filter is done, copy the non-Bindable variable to a Bindable one. You can see the updated demo using this approach here:

Demo 2
Source 2

This approach is about 10x faster! And only a little bit more work. In this case it’s very easy to be notified when the filter has completed and then update the Bindable variable:

if (event.kind == CollectionEventKind.REFRESH)
{
    ffCount = _ffCount;
}

In retrospect this seems like a silly mistake but I would not be surprised if this sort of thing is causing performance problems in many Flex applications. Data Binding is a very powerful part of Flex but it can also cause performance problems when used incorrectly. I hope this helps some of you to avoid this pitfall. Let me know what you think.

A few weeks ago I presented to developers in the QuickBase Developer Program about making Flex applications look and feel great by adding effects and by skinning components. Intuit has allowed me to repost that presentation here. Let me know what you think.

If you would like to be notified when “First Steps in Flex” is available we’ve setup a Google Group for book related announcements.

For those who just can’t wait to check it out… A preview of the book is now available! We’ve taken a few chapters from “First Steps in Flex” and created a DZone Refcard called “Very First Steps in Flex”. Please go “Vote Up” the announcement on DZone.com. Then go download the Refcard and let us know what you think. ]]> http://www.jamesward.com/wordpress/2008/08/18/very-first-steps-in-flex-now-available/feed/ http://www.jamesward.com/wordpress/2008/08/15/flex-show-with-bruce-eckel/ http://www.jamesward.com/wordpress/2008/08/15/flex-show-with-bruce-eckel/#comments Fri, 15 Aug 2008 16:28:57 +0000 James Ward http://www.jamesward.com/wordpress/?p=349 Listen to the Flex Show interview with Bruce Eckel and me. Then let me know what you think.

Atlanta - August 19, 2008 - Rich Internet Applications with Flex and Java

Chicago - August 20, 2008 - The Future of Flex, Flash Player, and AIR

Hope to see you there!

GeoWeb - Map Based RIA Development Using Adobe Flex and AIR with Duane Nickull

OSCON - Flex: the Open Source SDK for RIAs also with Duane

LinuxWorld - Building Rich Internet Applications with an Open Source Stack

I hope to see some of you at those conferences.