How can I make a deep copy in Objective-C?

Question

I'm learning ios development and I'm confused with deep copying in Objective-C. For example,I have three class below. Now I want to deep copy ClassA, can anybody teach me to finish the copy method?

A:

@interface ClassA : NSObject <NSCopying>  @property (nonatomic, assign) int aInt; @property (nonatomic, retain) ClassB *bClass;  @end 

B:

@interface ClassB : NSObject <NSCopying>  @property (nonatomic, assign) int bInt; @property (nonatomic, retain) ClassC *cClass;  @end 

C:

@interface ClassC : NSObject <NSCopying>  @property (nonatomic, assign) int cInt; @property (nonatomic, copy) NSString *str;  @end 

Answer 1

Following the explanation at http://www.techotopia.com/index.php/Copying_Objects_in_Objective-C

"This can be achieved by writing the object and its constituent elements to an archive and then reading back into the new object."

@implementation ClassA  - (id)copyWithZone:(NSZone*)zone{     NSData *buffer;     buffer = [NSKeyedArchiver archivedDataWithRootObject:self];     ClassA *copy = [NSKeyedUnarchiver unarchiveObjectWithData: buffer];     return copy; } @end 

Answer 2

You should add the copyWithZone: method in each class you want to be copiable.

NB: I wrote this by hand, watch out for typos.

-(id) copyWithZone:(NSZone *) zone {     ClassA *object = [super copyWithZone:zone];     object.aInt = self.aInt;     object.bClass = [self.bClass copyWithZone:zone];     return object; }  -(id) copyWithZone:(NSZone *) zone {     ClassB *object = [super copyWithZone:zone];     object.bInt = self.bInt;     object.cClass = [self.cClass copyWithZone:zone];     return object; }  -(id) copyWithZone:(NSZone *) zone {     ClassC *object = [super copyWithZone:zone];     object.cInt = self.cInt;     object.str = [self.str copy];     return object; }