NSCoding is a fantastically simple and convenient way to store data on iOS or Mac OS by turning your model objects directly into a file and then loading it back into memory again, without needing to write any file parsing and serialization logic. To save any object to a data file (assuming that it implements the NSCoding protocol), you can just do this:
Foo *someFoo = [[Foo alloc] init]; [NSKeyedArchiver archiveRootObject:someFoo toFile:someFile];
And to load it again later:
Foo *someFoo = [NSKeyedUnarchiver unarchiveObjectWithFile:someFile];
That’s fine for resources that are compiled into your app (such as nib files, which use NSCoding under the hood), but the problem with using NSCoding for reading and writing user data files is that, because you are encoding whole classes in a file, you are implicitly giving that file (with potentially unknown origin) permission to instantiate classes inside your app.