nscoding.m

// header.h
@interface CMTestEncoderNSCoding : NSObject <NSCoding>

@property (nonatomic, copy) NSString *aString;
@property (nonatomic, assign) NSInteger anInt;

@end

@interface CMTestEncoderNSCodingParent : CMObject

@property (nonatomic, strong) CMTestEncoderNSCoding *something;

@end

// .m

@implementation CMTestEncoderNSCoding

- (id)initWithCoder:(NSCoder *)aDecoder;
{
    if ( self = ([super init]) ) {
        self.aString = [aDecoder decodeObjectForKey:@"aString"];
        self.anInt = [aDecoder decodeIntegerForKey:@"anInt"];
    }
    return self;
}

- (void)encodeWithCoder:(NSCoder *)aCoder;
{
    [aCoder encodeObject:self.aString forKey:@"aString"];
    [aCoder encodeInteger:self.anInt forKey:@"anInt"];
}

@end

@implementation CMTestEncoderNSCodingParent

- (id)initWithCoder:(NSCoder *)aDecoder;
{
    if ( self = ([super initWithCoder:aDecoder]) ) {
        self.something = [aDecoder decodeObjectForKey:@"something"];
    }
    return self;
}

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


@end