iOS基础 Swift纯代码初始化项目(入口引导)

纯代码初始化项目首先在配置也做以下修改：删除Main Interface中的内容，则程序运行时会先去AppDelegate中执行相关的代码。
然后在Appdelegate.swift中添加如下代码：

class AppDelegate: UIResponder, UIApplicationDelegate {
    
    

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    
    
        //创建指定window
        window = UIWindow.init(frame: UIScreen.main.bounds)
        //指定window显示的控制器
        window?.rootViewController = nil
        //让window成为主windows且可访问
        window?.makeKeyAndVisible()
        
        return true
    }
}