Migration from Flex 3 to Flex 4

Question

I've migrated my project from flex 3 to flex 4 and all it's ok, the new project work fine.
But I created my custom TitleWindow MX style and I created a swc library from Flash builder 4, all it's ok.
When I use my custom TitleWindow in new project (compatible with mx+spark) it work fine when I add only mx component, when I add a <s:TextArea> for example, it throw this error in run-time: Skin for ForumTitleWindow1220.boxMessaggioInput.TextArea1227 cannot be found.
where ForumTitleWindow1220 and boxMessaggioInput are my instance.
in particolar the error is "throw(new Error(resourceManager.getString("components", "skinNotFound", [this])));"
in SkinnableComponent to line 698.
why?

Answer 1

For Flex 4, in addition to developing new "Gumbo" components
which have an improved skinning architecture and use TLF, the Flex
team is also planning to make it possible to have a few TLF
features such as bidirectional text in some or perhaps all of the
Halo components from Flex 3. These components currently use a
Player class known as TextField. A class called TLFTextField is
being developed which uses TLF to implement the same APIs as
TextField, and therefore can replace TextField in the Halo
components.
This work is underway but not yet complete. Only a few
components are currently working with this approach and there is no
way at the moment to turn on bidirectionality. We are also starting
to develop a UI-mirroring feature to allow the entire user
interface -- not just the text -- to become right-to-left.
So what you need -- the ability to write Arabic and Hebrew
applications using only legacy Halo components -- is planned for
Flex 4.
Gordon Smith
Adobe Flex SDK Team