Delegate not being called (instantiateViewControllerWithIdentifier)

Question

I have 5 instances of CalculatorViewController in my storyboard, but only one with identifier "secondOperationViewController". 3 of them connected with my initial ViewController named ContainerViewController using embed segues.

I want ViewController with identifier "secondOperationViewController" to call method from my ContainerViewController, but I cant correctly instantiate it, so delegate method not being called. Here is part of my code:

override func viewDidLoad() {
    super.viewDidLoad()
    secondOperationViewController = storyboard.instantiateViewControllerWithIdentifier("secondOperationViewController") as? CalculatorViewController
    secondOperationViewController!.delegate = self
    println(secondOperationViewController)
}

Any suggestions what's wrong here?

Also I found similar question:

Delegate in Swift-language

I rewrited instantion of my CalculatorViewController to:

override func prepareForSegue(segue: UIStoryboardSegue?, sender: AnyObject?) {
        secondOperationViewController = segue!.destinationViewController as? CalculatorViewController
        secondOperationViewController!.delegate = self;
    }

It works, but my delegate method is being called from all 3 ViewControllers, connected to initial ViewController, so I need another solution.

So how can I call delegate method exactly from ViewController with specified identifier? Any ideas?

---

So, embed segue doesn't work with "instantiateViewControllerWithIdentifier" (but works with modal presented segue). I dont know why. Here is solution for embed segue:

override func viewDidLoad() {
    super.viewDidLoad()
    let secondOperationViewController:CalculatorViewController = childViewControllers[0] as CalculatorViewController
    secondOperationViewController.delegate = self
}

Answer 1

In the storyboard give your segue a unique identifier:

Then in your prepareForSegue check against that before you set the delegate, this way you know exactly when you will be setting up this delegate.

override func prepareForSegue(segue: UIStoryboardSegue?, sender: AnyObject?) {
    // Checking to make sure this is the correct segue. This is also protection for the "as?"
    if segue?.identifier == "SecondOVCSeuge" {
        secondOperationViewController = segue!.destinationViewController as? CalculatorViewController
        secondOperationViewController!.delegate = self;
    }       
}