iOS: Archiving NSMutableArray

Question

I've Googled and searched SO for this with no straightforward results. It seems I have a fundamental misunderstanding of the following from Apple's documentation:

An archive can store an arbitrarily complex object graph. The archive preserves the identity of every object in the graph and all the relationships it has with all the other objects in the graph. When unarchived, the rebuilt object graph should, with few exceptions, be an exact copy of the original object graph.

Assume that I have an NSMutableArray that is a collection of Person objects. Each Person object implements initWithCoder and encodeWithCoder. Further, any given Person may have an NSMutableArray of objects (similarly coding-compliant) of Task.

My understanding is that there is a way to archive, thus triggering a cascading serialization of arbitrary depth, depending on implementation of the coding protocol. So in my view controller, I have a willEnterBackground that does:

data = [NSKeyedArchiver archivedDataWithRootObject:self.people];
// persist to NSUserDefaults

and I have a viewDidLoad that does:

// read from NSUserDefaults
self.people = [NSKeyedUnarchiver unarchiveObjectWithData:data];

This all happens, but two things:

1. The initWithCoder and encodeWithCoder in the objects contained by the people array are never called.
2. Unsurprisingly, the result is that self.people is an NSMutableArray of size 0. Surprisingly, the data that is unarchived is 252 bytes long, which looks about right.

Suggestions? Hints?

Answer 1

Even though you implemented those 2 methods, did you declare your Person class to be in the protocol ?