ios - Swift 无法分配类型为 'UINavigationController' 的值

Question

我是 Swift 的新手，所以我只是在学习。我正在关注 youtube 上的教程，但我一直收到此错误。让我们构建那个应用程序:如何构建 Twitter。“应用程序窗口应该在应用程序启动结束时有一个 Root View Controller ”

对于 window?.rootViewController = UINavigationController 它说

cannot assign value of type 'UINavigationController' to type UIViewController?' Expression of type'(rootViewController: HomeController)' is unused

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

var window: UIWindow?


func application(_ application: UIApplication,
                 didFinishLaunchingWithOptions launchOptions:
    [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.

    // ignore storyboard.
    window = UIWindow(frame: UIScreen.main.bounds)
    window?.makeKeyAndVisible()

    let homeController = HomeContoller(collectionViewLayout:
        UICollectionViewFlowLayout())
    window?.rootViewController = UINavigationController
        (rootViewController: homeController)

    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:.
}


}

Answer 1

删除这两行之间的换行符:

window?.rootViewController = UINavigationController
    (rootViewController: homeController)

第一行:

window?.rootViewController = UINavigationController

产生这个错误:

Cannot assign value of type 'UINavigationController.Type' to type 'UIViewController?'

第二行:

(rootViewController: homeController)

产生这个警告:

Expression of type '(rootViewController: HomeController)' is unused

如果你删除换行符，两者都会消失:

window?.rootViewController = UINavigationController(rootViewController: homeController)