Swift 4-无法调用委托方法

Question

I have one delegate method defined in one viewController like so:

import UIKit

protocol PatientsUserDelegate: NSObjectProtocol {

    func patientsUserDelegateMethod()

}

class PatientsUserController: UIViewController {

    var patientsUserDelegate: PatientsUserDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()

    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        print("Here")

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    @IBAction func nextButtonPressed(_ sender: Any) {

        patientsUserDelegate?.patientsUserDelegateMethod()

    }

}

What I am trying to do is call this delegate method in another viewController like so:

class PatientsRegistration: UIPageViewController, UIPageViewControllerDelegate, UIPageViewControllerDataSource, PatientsUserDelegate {

   var patientsUserController = PatientsUserController()

    override func viewDidLoad() {

         patientsUserController.patientsUserDelegate = self

    }

    func patientsUserDelegateMethod() {
        print("Here")
    }

}

nextButtonPressed gets called but not the delegate method is not being called in the first viewController I have. What am I doing wrong?

Answer 1

The problem is this line:

var patientsUserController = PatientsUserController()

The trouble is that this is not the same PatientsUserController that you actually want to talk to. It is a new PatientsUserController, a different one, that just floats in mid-air, with no relation to your running program. Thus, when you set the delegate...

patientsUserController.patientsUserDelegate = self

...you have set the delegate of the wrong PatientsUserController.

This is such a common beginner mistake that I've written a blog post about it:

http://www.programmingios.net/dont-make-a-new-instance-by-mistake/

As you'll see when you read that post, you need to get yourself a reference to the real PatientsUserController, the one that is already existing in your view controller hierarchy. How you do that depends on the relationship between your various view controllers.