Swift 4 委托不适用于标签栏控制器

我有一个带有 4 个视图的 tabbar 视图控制器，我在第 4 个视图上设置了一个协议，并使第一个视图符合这个协议。当我从第 4 个视图调用委托方法时，它不起作用，第 1 个和第 4 个视图控制器之间没有 segue。

我已经定义了我的协议，weak var delegate: delegateProtocol?然后在第一个视图控制器中进行了以下设置

class VC1: delegateProtocol {
    viewdidLoad(){
    var vc4 = VC4()
    VC4.delegate = self
  }

这是第四个视图控制器的片段

protocol SettingsDelegate: class {
    func locationDidSet(location: CLLocation)
}


class VC4: UIViewController {


  weak var delegate: SettingsDelegate?
 let controller = LocationPickerViewController()
 let navigationController = UINavigationController(rootViewController: controller)
 present(navigationController, animated: true, completion: nil)
  controller.completion = { location in
                self.location = location?.title ?? "Not found"
                defaults.set(location: location!.location, forKey: "location")
                self.tableView.reloadData()
                self.delegate?.locationDidSet(location: location!.location)
            }

这是第一个 ViewController 的片段

class MainVC: UIViewController, SettingsDelegate {
    func locationDidSet(location: CLLocation) {
        print(location.coordinate.latitude)
    }

  override func viewDidLoad() {
        super.viewDidLoad()
        settingVC = SettingsVC()
        settingVC?.delegate = self
}
}