Can a child view controller be the delegate of its parent view controller?

Question

Lets say there are two classes, class A and class B. Class B is a child view controller of A.

protocol ClassADelegate: class{
     functions
}
class A {
     code
     add B as child view controller
}


protocol ClassBDelegate: class{
     functions
}
class B {
     code
}

Considering that class A is the parent view controller of B, My question is if class A is a delegate of class B and class B is a delegate of class A, does that create an ownership cycle? Is this bad practice?

Answer 1

Delegates in Cocoa are stored as weak references. Weak references can't keep objects alive the way strong references do, thus you have no risk of strong reference cycles.

However, I can't think of a situation in which this would make sense. It's not really a delegate pattern anymore, it's just 2 objects arbitrarily messaging each other.

Answer 2

The parent should be the child's delegate.

The parent, if it needs to tell the child something, should just invoke methods.

Answer 3

if class A is a delegate of class B and class B is a delegate of class A, does that create an ownership cycle? Is this bad practice?

It doesn't necessarily produce a reference cycle. Normally, an object doesn't retain its delegate. As to whether it's bad practice, that depends. It's unusual, in that you'd normally expect that a delegate would have a lifetime at least as long as the object that it's delegating for, while you'd expect a child view controller to have a shorter lifetime than its parent. Without knowing more about your intended design, it's impossible to say for sure.