Weak Refrence in class return nil when created in first class's init

Question

im trying to create weak reference class in another class, in first class's init i create instance of second class to use it in a function, but after init function is done , second class get destroyed and return nil, here's a example code

//: Playground - noun: a place where people can play

import UIKit

class A {
    weak var b : B?
    init(){
        NSLog("a Created")
        self.b = B()
    
    }
    deinit{
        NSLog("a Destroyed")
    }
}

class B {
    var arrayOfA : Array <A> = []
    init(){
        NSLog("b Created")
       
    }
    deinit{
           NSLog("b Destroyed")
    }
    func printSomething(){
        NSLog("print Something")
    }
}


func test(){
    let a : A = A()
    a.b?.printSomething()
    NSLog("still in test()")
}

test()

in console i see this

2016-04-04 00:34:50.516 MyPlayground[20009:921709] a Created

2016-04-04 00:34:50.516 MyPlayground[20009:921709] b Created

2016-04-04 00:34:50.516 MyPlayground[20009:921709] b Destroyed

2016-04-04 00:34:50.527 MyPlayground[20009:921709] still in test()

2016-04-04 00:34:50.527 MyPlayground[20009:921709] a Destroyed

and calling printSomething() will return nil

i dont want create B class outside of A class and also i want it weak for memory leak problems.

some how i want one to many relationship between two swift class , so i can load data from function

Answer 1

Since you declare b as weak, it gets deallocated as soon as it goes out of scope. In this case, as soon this code:

init(){
  NSLog("a Created")
  self.b = B()
}

finishes execution, self.b gets destroyed. This is the expected behavior. If you want b to hang around after the init then you should leave it as strong.

Alternatively you can do this:

func test(){
  let b : B = B()
  let a : A = A(b:b)
  a.b?.printSomething()
  NSLog("still in test()")
}

In A you can make a special init that takes in a B:

init(b: B){
  NSLog("a Created")
  self.b = b
}

With this code, A's reference to B is still weak, but since the B is still around in the test() method, it's also there when printSomething() is called.