Swift 类被分段时userDefualt不保存开关

我的swift代码下面是所有代码，没有故事板。尝试使用用户默认值保存交换机的状态。因此，当用户切换到twoViewController，然后切换回ViewController时。未保存用户开关设置。没有出现错误，我不知道发生了什么

import UIKit

class ViewController: UIViewController {
    var nxtBTn = UIButton()
    var mySwitch =  UISwitch()

    let userDefaults = UserDefaults.standard

    var firstTimeAppLaunch: Bool {
        get {
            // Will return false when the key is not set.
            return userDefaults.bool(forKey: "firstTimeAppLaunch")
        }
        set {}
    }



    @objc func switchAction(_ sender: UISwitch) {
        userDefaults.set(sender.isOn, forKey: "mySwitchValue")
    }
   @objc func press() {
        let segue = twoViewController()

        segue.modalPresentationStyle = .fullScreen // actually .fullScreen would be better
        self.present(segue, animated: true)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        [nxtBTn,mySwitch].forEach {
            $0.translatesAutoresizingMaskIntoConstraints = false
            view.addSubview($0)
            $0.backgroundColor = .green

        }
        if !firstTimeAppLaunch {
            // This will only be trigger first time the application is launched.
            userDefaults.set(true, forKey: "firstTimeAppLaunch")
            userDefaults.set(true, forKey: "mySwitchValue")
        }

        NSLayoutConstraint.activate([

            nxtBTn.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            nxtBTn.topAnchor.constraint(equalTo: view.topAnchor),
            nxtBTn.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 7/7, constant: 0),
            nxtBTn.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.4, constant: 0),

            mySwitch.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            mySwitch.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            mySwitch.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 7/7, constant: 0),
            mySwitch.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.4, constant: 0),

        ])
        mySwitch.addTarget(self, action: #selector(switchAction(_:)), for: .touchDown)
             nxtBTn.addTarget(self, action: #selector(press), for: .touchDown)

        view.backgroundColor = .white
    }

    override func viewDidAppear(_ animated: Bool) {

                mySwitch.isOn = userDefaults.bool(forKey: "mySwitchValue")
    }

}
class twoViewController : UIViewController{

    var backBtn = UIButton()

    override func viewDidLoad() {
        super.viewDidLoad()
        backBtn.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(backBtn)
        backBtn.backgroundColor = .systemGreen


        NSLayoutConstraint.activate([

            backBtn.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            backBtn.topAnchor.constraint(equalTo: view.topAnchor),
            backBtn.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 7/7, constant: 0),
            backBtn.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.4, constant: 0),


        ])

        backBtn.addTarget(self, action: #selector(oneVC), for: .touchDown)


    }

    @objc func oneVC(){
        let segue = ViewController()

        segue.modalPresentationStyle = .fullScreen // actually .fullScreen would be better
        self.present(segue, animated: true)
    }
}

---

无论你在哪里说：。着陆都是错误的。将所有选项都更改为：.primaryActionTriggered，事情会有所改善。

无论您在哪里说：.Taunddown的

，都是错误的。将它们全部更改为：.primaryActionTriggered的
，事情会有所改善。
在我的情况下，它工作得非常好。你能解释一下性能上的差异吗？在我的情况下效果很好。你能解释一下性能上的差异吗？