Swift委托不在父级中调用函数

Question

I am trying to get a child view controller, which is displayed in a view container at the bottom part of the main, parent View Controller. When I press the button in the child, "Button pressed from Basic VC" prints to the console, but "Warm button pressed from main VC" does not. I need the function that prints that second message to be called in the main View Controller. Here is the relevant BasicViewController code:

protocol BasicVCDelegate: class {
    func warmButton()
}

class BasicViewController: UIViewController {
    weak var BasicVCDelegate: BasicVCDelegate?

    @IBOutlet weak var warmButton: UIButton!

    @IBAction func warmButton(sender: AnyObject) {
        print("Button pressed from Basic VC")
        BasicVCDelegate?.warmButton()
    }
}

And from ViewController.swift

class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate, BasicVCDelegate {
    override func viewDidLoad() {
        pauseButton.isEnabled = false

        hideAll();
        self.basicContainer.isUserInteractionEnabled = true;
        self.basicContainer.isHidden = false;

        self.timerLabel.text = String("00:00:00");

        eventTable.dataSource = self
        eventTable.delegate = self

        loadEvents(event: "timer start")
        super.viewDidLoad()
    }

    // CREATE SEGUEs
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let nav = segue.destination as? UINavigationController, let classBasicVC = nav.topViewController as? BasicViewController {
            classBasicVC.BasicVCDelegate = self
        }
    }

    // FUNCTIONS FOR BASIC VIEW CONTROLLER TO REFERENCE
    func warmButton() {
        print("Warm button pressed from main VC")
    }
}

EDIT: From everyone below, it seems that the following section of code in ViewController is causing the issue (the line within the if statement is never being called):

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let nav = segue.destination as? UINavigationController, let classBasicVC = nav.topViewController as? BasicViewController {
        classBasicVC.basicVCDelegate = self
    }
}

This is probably due to my unfamiliarity with delegates and the prepareforsegue function. Need help figuring out what should follow that "if let"

EDIT 2: Replaced the above code with the following as per some users' suggestion (still not reaching the print statement):

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let nav = segue.destination as? BasicViewController, let classBasicVC = nav.basicVCDelegate {
        print("got here!!")
    }
}

FINAL EDIT: Thank you for your help! After some playing around, the following works (aside from a warning that changes to an error when I address it - I can live with a warning).

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let nav = segue.destination as? BasicViewController, let classBasicVC = nav as? BasicViewController? {
        classBasicVC?.basicVCDelegate = self
    }
}

Answer 1

It should be this instead of your last edited code:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let classBasicVC = segue.destination as? BasicViewController {
        classBasicVC.basicVCDelegate = self
    }
}

Answer 2

You haven't assigned button's delegate to the ViewController

Add this to your ViewController's viewDidLoad

    override func viewDidLoad() {
    //other code 
    yourButton.BasicVCDelegate = self
    }

Also its a good practice to use camel case for delegate variable like this basicVCDDelegate