Understanding retain cycle in depth

ios objective-c memory-management automatic-ref-counting retain-cycle
Tariq picture Tariq · Nov 10, 2013 · Viewed 39.1k times · Source

Lets say we have three objects: a grandparent, parent and child. The grandparent retains the parent, the parent retains the child and the child retains the parent. The grandparent releases the parent.

What will happen in this case ?

Answer

rmaddy picture rmaddy · Nov 10, 2013

Unless there is some other reference to the parent or child, they both become orphaned. But the retain cycle between the parent and child prevent either from being released and they become wasted memory.

A child should never retain a parent. If anything, use a weak reference in the child to maintain a reference to the parent.

Related questions

Is it possible to debug "Terminated due to memory error"?

In a certain (consistent) point when my app is running, I consistently get the xcode error message Terminated due to memory error. I cannot find the code causing the error, but I can tell what code is near the error (…

Read More
In which situations do we need to write the __autoreleasing ownership qualifier under ARC?

I'm trying to complete the puzzle. __strong is the default for all Objective-C retainable object pointers like NSObject, NSString, etc.. It's a strong reference. ARC balances it with a -release at the end of the scope. __unsafe_unretained equals the …

Read More
ARC and autorelease

autorelease is used for returned function object so the caller don't take ownership and callee will release the object in the future. However, ARC is capable to count ownership of caller and release it after use, that is, it can …

Read More