Explain Objective C retain cycle with real world example?

Question

I am reading about retain cycle that, "A retain cycle can take a few forms, but it typically means that object A retains object B, and object B retains object A, but nothing else retains object A or B". But I'm not clear about that concepts. Please can anyone explain retain cycle with real world example.

Thanks.

Retain cycles can be considered as Deadlocks. If you are not able to find a good example of retain cycle, find one for deadlock. — Vinay Jain, Dec 11 '15 at 05:48
Retain cycle is all about memory in objective-c management we know that.If you want to know the process with a real life example.Take the case of a form filling in a hall with 1000 people and 10 pens. — Rahul K Rajan, Dec 11 '15 at 06:02

score 7 · Accepted Answer · answered Dec 11 '15 at 05:52

A simple example,a person lives in a department,a department have one person(Suppose have one)

@class Department;

@interface Person:NSObject
@property (strong,nonatomic)Department * department;
@end

@implementation Person
-(void)dealloc{
    NSLog(@"dealloc person");
}

@end
@interface Department: NSObject
@property (strong,nonatomic)Person * person;
@end

@implementation Department
-(void)dealloc{
    NSLog(@"dealloc Department");
}
@end

Then call it like this

- (void)viewDidLoad {
    [super viewDidLoad];
    Person * person = [[Person alloc] init];
    Department * department = [[Department alloc] init];
    person.department = department;
    department.person = person;
}

You will not see dealloc log,this is the retain circle

Can you explain a bit about the implementation. – Rahul K Rajan Dec 11 '15 at 06:06 — Rahul K Rajan, Dec 11 '15 at 06:06

Rahul K Rajan · Answer 2 · 2020-05-29T06:05:53.967

A retain cycle is a situation when object "First" retains object "Second", and object "Second" retains object "First" at the same time*. Here is an example:

@class Second;
@interface First : NSObject {
Second *second; // Instance variables are implicitly __strong
}
@end

@interface Second : NSObject {
First *first;
}
@end

You can fix a retain cycle in ARC by using __weak variables or weak properties for your "back links", i.e. links to direct or indirect parents in an object hierarchy:

__weak First *first;

Explain Objective C retain cycle with real world example?

2 Answers2