What steps are necessary to cause a Retain Cycle in memory?

A retain cycle in iOS occurs when two or more objects hold strong references to each other, preventing them from being deallocated, which causes a memory leak.

The steps to create a retain cycle are:

1. Object A holds a strong reference to Object B.
2. Object B holds a strong reference to Object A.
3. Neither object is deallocated because the reference count does not reach zero.

Example:

class A {
    var b: B?
}

class B {
    var a: A?
}

let a = A()
let b = B()
a.b = b
b.a = a // Retain cycle

To avoid a cycle, one of the references is made weak (weak) or unowned (unowned). For example:

class B {
    weak var a: A?
}

Thus, a retain cycle occurs when mutual strong references are maintained without breaking the cycle, which blocks the deallocation of objects.