How to copy a custom Objective-C object?

Question

I have a class, say the class Person. In than class I have several NSMutableArrays.

@property NSMutableArray *arrayOne;
@property NSMutableArray *arrayTwo;
...

Now I want to copy that Class so I can return it from a function and use the copy and change it's data. I want to have a new copy of the object in memory not another reference to the same address.

To do that I have implemented this in my Person.m:

-(id)copyWithZone:(NSZone *)zone
{
    Person *copy = [[Person allocWithZone:zone] init;
    copy.arrayOne = [NSMutableArray arrayWithArray:self.arrayOne];
    copy.arrayTwo = [NSMutableArray arrayWithArray:self.arrayTwo];
    ...

    return copy;
}

So far this works just like I want it to, but when I try to sort the arrays of the copy, I get an error: -[__NSArrayI sortUsingSelector:]: unrecognized selector sent to instance 0x100108a30

I have noticed that the original arrays are of the type '_NSArrayM' but the copy is '_NSArrayI'...

So what did I wrong? I have heard of deep copying using NSArchiver and NSUnarchiver... Do I have to use that? Sorry, I am quite new to C and Objective-C... :D

I hope you can help me out of this. =)

Sorry about my 'school-english'....

Cheers, Nick

EDIT: The arrays consist of NSString objects, so I can use

sortUsingSelector:@selector(caseInsensitiveCompare:)

to sort the array.

Answer 1

How are your mutable array properties being declared in your header file?

// Wrong
@property (copy) NSMutableArray *array;
@property (assign) NSMutableArray *array;

// Right
@property (strong) NSMutableArray *array;

NB If you're just doing

@property NSMutableArray *array;

then I'm amazed your code has got this far :) The default property memory semantics is assign - which won't tell ARC to retain your arrays in any way at all :) You need to specify strong.