NSDictionary -> NSData:
NSMutableData *data = [[NSMutableData alloc] init];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
[archiver encodeObject:yourDictionary forKey:@"Some Key Value"];
[archiver finishEncoding];
[archiver release];
// Here, data holds the serialized version of your dictionary
// do what you need to do with it before you:
[data release];
NSData -> NSDictionary
NSData *data = [[NSMutableData alloc] initWithContentsOfFile:[self dataFilePath]];
NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
NSDictionary *myDictionary = [[unarchiver decodeObjectForKey:@"Some Key Value"] retain];
[unarchiver finishDecoding];
[unarchiver release];
[data release];
You can do that with any class that conforms to NSCoding.