巴顿什么也没做...？肖恩·艾伦的教程

如何解决巴顿什么也没做...？肖恩·艾伦的教程

今天，我由Sean Allen在youTube上做了一个关于Swift中编程基础知识的快速教程，我像他的代码一样正确地使用了所有代码，但是我的Next Button却什么也不做，我不明白为什么？这是该教程的链接：https://www.youtube.com/watch?v=1hCwOIgjLBA&list=LLN6Oo-N18qzBYtBI-iiCS2A&index=3

这是我的FirstViewController：

import UIKit

class ViewController: UIViewController {

    let nextButton = UIButton()
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setUpNetButton()
        view.backgroundColor = .yellow
        
    }
    
    func setUpNetButton() {
        nextButton.backgroundColor = .blue
        nextButton.setTitleColor(.white,for: .normal)
        nextButton.setTitle("NEXT",for: .normal)
        
        nextButton.addTarget(self,action: #selector(nextButtonTapped),for: .touchUpInside)
        
        
        view.addSubview(nextButton)
        setUpNextButtonConstraints()
    }
    
    @objc func nextButtonTapped() {
        let nextScreen = SecondViewController()
        nextScreen.title = "Second Screen"
        navigationController?.pushViewController(nextScreen,animated: true)
    }
    
    
    func setUpNextButtonConstraints() {
        nextButton.translatesAutoresizingMaskIntoConstraints = false
        nextButton.leadingAnchor.constraint(equalTo: view.leadingAnchor,constant: 20).isActive = true
        nextButton.trailingAnchor.constraint(equalTo: view.trailingAnchor,constant: -20).isActive = true
        nextButton.heightAnchor.constraint(equalToConstant: 50).isActive = true
        nextButton.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
    }
    
    
    }

这是我的第二个屏幕：

import UIKit

class SecondViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemBlue
    }


}

这是我的AppDelegate：

import UIKit
import CoreData

@UIApplicationMain
class AppDelegate: UIResponder,UIApplicationDelegate {

var window: UIWindow?

    func application(_ application: UIApplication,didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        
        let viewController = ViewController()
        let navigationController = UINavigationController(rootViewController: viewController)
        
        window = UIWindow(frame: UIScreen.main.bounds)
        window?.rootViewController = navigationController
        window?.makeKeyAndVisible()
        
        
        return true
    }

... 我真的不明白吗我知道问题之一是NavigationBar，它也没有出现！ 谢谢！