Saving an NSDictionary of NSArrays of custom objects

I have a dictionary (it's mutable if that makes a difference) which contains nsarrays, which in turn contain (subclass of NSObject)s I have implemented initWithCoder and encodeWithCoder like this:

-(id)initWithCoder:(NSCoder *)aDecoder {
    self = [super init];
    self.Title = [aDecoder decodeObjectForKey:@"Title"];
    self.SiteAPIU开发者_JAVA百科RL = [aDecoder decodeObjectForKey:@"SiteAPIURL"];
    self.ID = [aDecoder decodeObjectForKey:@"ID"];
    return self;
}

-(void) encodeWithCoder:(NSCoder *)aCoder {
    [aCoder encodeObject:self.Title forKey:@"Title"];
    [aCoder encodeObject:self.SiteAPIURL forKey:@"SiteAPIURL"];
    [aCoder encodeObject:self.ID forKey:@"ID"];
}

But it doesn't save properly when I do [dictionary writeToFile:savepath atomically:YES]; So what am I doing wrong, and what exactly is serialization and do I need I need to use NSKeyedArchiver or something?

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[NSDictionary writeToFile: atomically:] uses NSPropertyListSerialization, which can only record a subset of primitive objects (numbers, strings, dates and data). So while you could use NSCoding along with NSKeyedArchiver to archive the objects, another option is to marshal your objects into a string or data representation, store that in the property list, and unmarshal them again on loading.

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Yes, you want to use a NSKeyedArchiver

All the info you need can be found here:

http://developer.apple.com/library/ios/ipad/#documentation/Cocoa/Conceptual/Archiving/Archiving.html