Can I get all keys of a NSKeyedUnarchiver?

I want do something with these step:

1. Encode a kind of object A with NSKeyedArchiver M and I can get a NSData X.
2. Init another kind of object B with NSKeyedUnarchiver N from NSData X. The names of A and B are the same, so it's possible(I have done an experiment).
3. And then I want to enco开发者_运维知识库de B, but I do not know wether B lose some data of X, 'cause A and B may have different number of property.

So I want to get all keys and values from N. How can I do this?

I do not understand NSKeyedUnarchiver well, please help me.