Question

Can any one explain Retain cycle with example code(Objective C) ? and How can we remove retain Cycle ?(with code or diagram). I know about it theoretically but i never come across such kind of program ? I am very curious to see, how retain cycle solved (with code or diagram) ?

Answer 1

Delegation is one example where you have to avoid a retain cycle by using the assign attribute on a delegate property. For example, you have a parent object which creates a child:

self.child = [[[Child alloc] init] autorelease];

So the parent has a retained reference to the child (because the property setter retains it).

Now the parent sets itself as a delegate on the child:

self.child.delegate = self;

Now, if the child retains its delegate property there is a retain cycle. Both contain references to the other and cannot be deallocated.

To avoid this the child declares the delegate property with the assign attribute:

@property (nonatomic, assign) id delegate;

This is safe because a delegate will almost always outlive the delegator. If not, the parent should set the child’s delegate to nil before it goes away.