How to pass Objective-C class instance variable to another class instance variable without object reference?

Question

I have Three class A ,B and C.

@interface ClassA

@property (nonatomic,strong) NSMutableArray *classCArray;

@end

@implementation ClassA 
...
@end

@interface ClassB

@property (nonatomic,strong) NSMutableArray *classCArray;

@end

@implementation ClassB
...
@end

@interface ClassC

@property (nonatomic,strong) NSString *name;

@end

@implementation ClassC
...
@end

Then I create instance "a" of Class A, set "a" variable classCArray ,and pass a.classArray to "b"(instance of ClassB).

ClassA *a = [ClassA alloc] init];
ClassC *cInClassA = [ClassC alloc] init];
cInClassA.name = @"jack";
[a.classCArray addObject:c];

ClassB *b = [ClassB alloc] init];
b.classCArray = a.classCArray;
ClassC *cInClassB = b.classCArray[0];
cInClassB.name = @"Bob";

After above code , cInClassA.name changed.(eauqls "Bob") I don't hope this happen. How I can do ?

CRD · Accepted Answer · 2017-05-13 07:38:12Z

2

You seem to be assuming that assignment copies objects, it does not. A variable, such as your a, can only ever store a reference to an object and assignment copies the reference.

Your code creates 4 objects: instances of ClassA and ClassB referenced by a and b respectively; a single instance of NSMutableArray referenced by both a.classCArray and b.classCArray; and a single instance of ClassC referenced by the mutable array and variables cInClassA and cInClassB.

If you wish to create a copy of an object use the method copy, or for a mutable copy of a mutable object use mutableCopy.

HTH

answered May 13, 2017 at 7:38

CRD

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1 Comment

Seppuu Over a year ago

Thank you.I implemented - (id)copyWithZone:(NSZone *)zone;for ClassC(this is a NSCopying method in cocoa),then use [myObject copy],it worked!.

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