When do you use encodeWithCoder: and initWithCoder: on the iPhone?

Question

As my question in the subject above states, what requirements do you typically have to meet in order to say "Ok, I need encodeWithCoder: and initWithCoder: instantiation for this"? Typically you can write object state to NSUserDefaults, so I'm curious when do you experts decide to use one vs the other?

Answer 1

initWithCoder: is used by the OS when un-archiving XIB files; if you look closely, you'll see that initWithFrame: is not called for views you create in your XIB; they'll have initWithCoder: called instead.

Answer 2

User defaults is, basically, a property list. Property lists are similar to JSON and can only store specific types of data -- NSString, NSNumber, NSData, NSDate, NSArray, NSDictionary. If you try to store anything else in a user default, you'll get an exception. Property lists also can't handle arbitrary object graphs, only trees.

You could always take your custom state and convert it into a property-list compatible data structure, then store it in user defaults; but then you're basically implementing an object serialization mechanism, and you might as well use the more powerful one that's already provided by NSArchiver.

Answer 3

NSCoder is the standard Cocoa method of implementing serialization. See Apple's Archives and Serializations Programming Guide for Cocoa for details.