Swift 4从自定义ViewController开始

import UIKit

class CustomViewController: UIViewController {
    // 在这里实现你的自定义逻辑和界面
}

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // 创建一个UIWindow对象
        window = UIWindow(frame: UIScreen.main.bounds)
        
        // 设置自定义ViewController为根视图控制器
        let customViewController = CustomViewController()
        window?.rootViewController = customViewController
        
        // 设置窗口可见
        window?.makeKeyAndVisible()
        
        return true
    }
}