It's good to see that flex 4 has been released, and I am now in the process of updating our software from the beta 2 to the final release.
There are a few problems along the way though, most notably the lack of backward compatibility: http://opensource.adobe.com/wiki/display/flexsdk/Compatibility+Mode+SWC+Policy+(Mini+Speci fication). Does this mean that we need to choose between spark or halo?
The specific problem we are having (which I *think* is due to this backwards compatibility problem) is that we need to specify the halo theme when compiling, because we cannot set backwards compatibility to 3.0 any more. I am hypothesising that this means that the spark theme is *not* included (as per link above), and therefore all the joy found inside frameworks/libs/spark.swc/defaults.css (where there appears to be a lot of default skinClasses defined.
Error: Skin for * cannot be found. at spark.components.supportClasses::SkinnableComponent/attachSkin()
In our case, the component for which the skin cannot be found is the MXML generated: flexwrapper0.ApplicationSkin2._ApplicationSkin_Group1.contentGroup._flexwrapper_VGroup1.G roup22.contentVGroup.layoutModules.dashboard.contentGroup.dashboard372.contentGroup.
So does this look like something that would be related to using the halo theme? And if so, is it even still possible to use both halo and spark components in the same application?
I think you can use MX and Spark components in the same application, although you will have extra work to do around namespaces and (possibly) CSS.
See page 3 of Joan Lafferty's "Differences between Flex 3 and Flex 4" article for more infomation: http://www.adobe.com/devnet/flex/articles/flex3and4_differences_03.html
Flex Doc Manager