Objective-C: Retain cycle

Objects in a hierarchy are created, owned and freed in a chain along the hierarchy.

In its most simple form, a retain cycle occurs when two objects keep a strong reference to each other since both objects do retain each other, making it impossible to release.

With ARC you avoid retain cycles by declaring one of the items as a weak reference. For instance, delegate properties should be weak. A weak reference means the property can become invalid.

@property (weak, nonatomic) id *delegate;

Another thing to consider is indirect references, ie collections. NSArray will retains it's contents.

From this great article, we get five rules:

• An object must never retain its parent
• No hierarchical ancestor can be retained
• "Connection" objects should not retain their target
• Use "close" methods to break cycles
• Temporary retains must be temporary