AS3 Customized Serialization and Deserialization, IExternalizeable to the rescue! September 12, 2007

This and original off Pete's blog is great article on a little known feature critical for de/serialization in flash, and the knowledge is not just for client/server as the  The flex documentation on the subject implies. Anywhere the AMF format is used: shared local objects, local connection, in AIR using fileStream. cloning objects using ByteArray etc. So many gems (might as well be easter eggs!) in the AS3 code, sadly barely documented. It's using IExternalizeable for custom serialization, which mimicks Java's already proven approach.

What's that mean? It means you can better control how objects are written and read back from the byteStream.
What if I don't want X to be written?
To compliment a great follow up on using the [Transient] metadata by Darron, with both the clone and when serializing to disk or the web. I've got to say the metadata format makes sense but also wierds me out.

How do I get my class type back

registerClassAlias is necessary for local cloning and maintaining Class type, when written to a ByteArray they forget which class they belong to. I would have hoped that the RemoteClass metadata would have worked but that was not the case. Anyway you can do this via a static var:

private static const REG:* = registerClassAlias("reflection.IntrospectableObj",IntrospectableObj);

this is called during static initialization, once which is all that's really needed as the linkage is static, not per instance.

What if you need to transcend versions of code?

basic approach to using serialization to deal with different versions of the class is
1) write a version number to the stream first, then a) save to hashmap, or b) iterate over the members that should be saved.
2) read the version number back from the stream, then reconstitue the members from a) the Dictionary (like Remotings's ASObject) or b) in the order they were written to the stream. Vary the parsing response upon the version number.

Summary of Serialization Tips:

1) Use IExternalizable to customize how your objects are written.

2) Use the [Transient] metadata to NOT serialize objects if you don't want them there, and are using writeObject().
3) registerClassAlias is necessary for local cloning and maintaining Class type. You can do this via a static var,
private static const REG:* = registerClassAlias("reflection.IntrospectableObj",IntrospectableObj);

4) keep a unique version number in the code, write a version first in the output stream then when reading it back perform different behavior based on that stream. The use of a Dictionary for key/values can be helpful too.