Flash allows you to import native Illustrator files, but since it supports only up to Illustrator 7 files reliably, you can't use this method to import transparency, symbols, soft-edged images, or other objects from later versions of Illustrator. Exporting a SWF from Illustrator will convert objects into Flash-friendly artwork more reliably, but when you import a SWF into Flash, the contents come in as a single layer regardless of whether it existed on multiple layers when it was created. So, how do you get the best of both worlds?
The short answer: export each layer as a separate SWF and import all SWFs into Flash simultaneously, paying attention to the order in which you add them to the import dialog box; or, export each layer as a SWF frame, then manually distribute each frame to a new layer. For the details on how & why to use either method, read on.
::> Option 1: Export Illustrator layers as frames
You can export a SWF from Illustrator either by choosing File->Export and selecting SWF in the popup menu, or by choosing File->Save for Web and designating one or more slices as SWF. The File->Export method gives more control over bitmap compression options; the Save for Web method lets you mix SWFs and bitmap formats in a sliced HTML layout.
Using either method you can export Illustrator layers as SWF frames:
::> Option 2: Export Illustrator layers as separate SWFs
You can also use File->Export to turn each Illustrator layer into a separate SWF. The main advantage with this approach is that if you import all SWFs simultaneously, Flash will put each on its own layer, effectively recreating your Illustrator layer stack. The main disadvantage is that if you're using symbols in Illustrator, a symbol used across multiple layers will be imported into the Flash library repeatedly. Flash is sometimes but not always clever enough to export the symbol just once when it creates a SWF, but the task of scripting or editing imported symbols is made more difficult. If you discover that your symbol artwork is being exported repeatedly from Flash, or if the extra symbols bug you, you could always do the following:
The behavior of Flash's Import dialog differs across operating systems and from version to version of Flash in ways that can affect the stacking order of layers.