Migrate Flex 4 Beta 2 to Latest Nightly Builds

I have a project based on Flex 4 Beta 2 and now I wanted to migrate to the latest nightly build since there were many important fixes.
Things have changed so here what I did to get my project up and running again:

Halo is now mx

The namespace for halo (Flex 3) components changed from xmlns:mx=”library://ns.adobe.com/flex/halo” to xmlns:mx=”library://ns.adobe.com/flex/mx”. Just do a quick search and replace and this one is solved. Also do not forget to update you CSS file namespace to @namespace mx “library://ns.adobe.com/flex/mx”;

Flex 3 compatibility mode is gone

My project originally was based on Flex 3 so I used the Flex 3 compatibility option in Flex 4 Beta 2. This does not seem supported anymore and you get lots of dependency errors for halo/mx components that they require at least 4.0.0. So disable the Flex 3 mode and select the halo theme to be still compatible with Flex 3 aka halo components.


I build my AIR project with Ant so I had to define to use the halo theme:

<compiler.theme dir="${flex.sdk.dir}/frameworks/themes/Halo/">
	<include name="halo.swc" />

In my case I switched to build and it looks pretty cool. The compiler seems faster and my app in general performed well. There is now also a Spark ToggleButton but a few things are still missing like IconButton, SparkAlert and so on. Anyway, I use Flex 4 for production already and feel pretty solid about it. The workflow is way better than with Flex 3 because of the new state syntax, better skinning, FXG, light weight groups etc.

5 comments to Migrate Flex 4 Beta 2 to Latest Nightly Builds

  • baduncaduncan

    I totally agree – flex 4 is an awesome upgrade from flex 3! I’m a little amazed at how much they’ve managed to keep backwards compatible actually. They even extended the original halo components to match the new workflow of the states syntax and such.

  • Keith T

    Thanks you so much!!! I couldn’t find anywhere a soloution to why some of my mx:…. were no longer recognized, pissed that there isn’t some way to have found out the namespace change easier…

  • Support for compatibility with Flex 2 and earlier has been removed, but Flex 3 compatibility mode is supported.

    In Flash Builder you should be able to go to Project > Properties > Flex Compiler and check “Use Flex 3 compatibility mode”.

    Note that while using Flex 3 compatibility mode you will be limited to Flex 3 components and won’t be able to add any spark features or components including s:Application.

    If you want to mix and match halo and spark components, but still have the halo components look like they used to in Flex 3 then you can change the theme.

    Here is a link to more information on what compatibility mode does other than just changing the theme:


  • Hi,

    are you still using or did you upgrade to the latest stable nighlty builds from 29th of January? I wanted to upggrade from beta 2 to 13875 yesterday and have problems (it seems it doesnt work even if it is stable nightly build, please read more here

    and here is discussion on http://forums.adobe.com/thread/552806?tstart=0

    I’m still searching for latesta stable nightly build, which really works and it seems works for you, so I can try it as well.

  • Eli Renato


    I´m trying to compile using the Sky theme, but, I can´t find the file sky.swc on the frameworks/themes directory. Do yout know how can I set default themes.

    PS: I trying to compile without use Flex Builder 4, just, using Ant tasks.