Easy way to archive interlinked objects

Question

In a game I have a bunch of objects and collections of objects, some of them include references to others. Is there a straightforward way to archive them - to save a game state - while maintaining those references? If I understood well, NSArchiver can do that, but it wasn't available on SDK 2, is it on SDK 3?

(I have sort of asked this question before (http://stackoverflow.com/questions/307681/best-way-to-save-load-iphone-game-data) but SDK 3 has been released in the meantime, and I'd like to know if this topic has progressed.)

Answer 1

Check out Object serialization here:

Encoding/Decoding Objects (apple.com)

Basically, you have to make your classes Key-Value Coding compliant, to properly save all of your data; It archives them into binary property lists. After you write your initWithCoder: and encodeWithCoder: functions it's pretty much automatic!

Answer 2

You need to make all of the classes you want to serialize implement the NSCoding protocol. After that, you need to encode them with the NSKeyedArchiver class. That class will recursively serialize your objects, and will deal with cycles. NSKeyedArchiver is available in all releases of the iPhone SDK. To decode your objects, you'll uses NSKeyedUnarchiver.