Question

例如，在作为UIViewcontroller的子类的MainViewController中，我覆盖了nib名称变量并返回了一个字符串来满足参数，但是在appDelegate中我能够简单地将一个对象分配给rootViewController变量而不使用术语覆盖。我理解关键字覆盖意味着重写一个由子类继承的方法，但是我不理解它在这个意义上我们使用变量。

AppDelegate.swift代码：

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    var mainViewController: MainViewController?


    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

        //so as this function fires we need to put forth some effort.....from inside this function instantiate a view controller
        let mainViewController = MainViewController()

        //put the view of the ViewController on screen
        //mainViewController.show(mainViewController, sender: self)

        window?.backgroundColor = UIColor.purple


        window?.rootViewController = mainViewController


        //set the property to point to the viewController
        self.mainViewController = mainViewController


        return true
    }

    func applicationWillResignActive(_ application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
    }

    func applicationDidEnterBackground(_ application: UIApplication) {
        // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
        // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
    }

    func applicationWillEnterForeground(_ application: UIApplication) {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
    }

    func applicationDidBecomeActive(_ application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    }

    func applicationWillTerminate(_ application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    }


}

MainViewController.swift代码：

import Foundation
import UIKit

class MainViewController: UIViewController {

    override var nibName: String? {
        return "MainViewController"
    }

}

Answer 1

nibName是一个只读属性 - 检查公共UIViewController界面显示：

open var nibName: String? { get }

nibName能够在UIViewController实例的生命周期内进行更改是没有意义的，因此将其作为只读属性确保它只是一种配置形式。

为什么我们覆盖最初为零的变量而不是简单地设置它们？

1 个答案: