ios - 支持 iOS 12 和 13 时的 AppDelegate 和 SceneDelegate

Question

我需要支持 iOS 12 和 iOS 13。

我应该在 AppDelegate 之间复制代码吗？和 SceneDelegate ?

例如:

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    guard let windowScene = (scene as? UIWindowScene) else { return }
    let window = UIWindow(windowScene: windowScene)

    window.rootViewController = HomeViewController()
    window.makeKeyAndVisible()

    self.window = window
}

和

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    let window = UIWindow(frame: UIScreen.main.bounds)
    window.rootViewController = HomeViewController()
    window.makeKeyAndVisible()

    self.window = window

    return true
}

如果我不这样做，在 1 版本中我会出现黑屏，但如果我这样做并在 viewDidLoad 中打印 HomeViewController的方法我可以看到它被调用了两次。

我更新了我的 didFinishLaunchingWithOptions我可以在 iOS13 中看到它仍然被调用两次。

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

    guard #available(iOS 12, *) else { return true }

    let window = UIWindow(frame: UIScreen.main.bounds)
    window.rootViewController = HomeViewController()
    window.makeKeyAndVisible()

    self.window = window

    return true
}

Answer 1

您确实需要复制代码，但您需要确保它仅在正确的系统上运行。在 iOS 13 中，您不希望该应用程序委托(delegate) didFinishLaunching要运行的正文代码，因此请使用可用性检查来防止它。
同样，使用可用性从 iOS 12 中隐藏窗口场景的东西。

这是在 iOS 12 和 iOS 13 上都能正常运行的解决方案的基本草图:

AppDelegate.Swift

import UIKit
@UIApplicationMain
class AppDelegate : UIResponder, UIApplicationDelegate {
    var window : UIWindow?
    func application(_ application: UIApplication,
        didFinishLaunchingWithOptions 
        launchOptions: [UIApplication.LaunchOptionsKey : Any]?)
        -> Bool {
            if #available(iOS 13, *) {
                // do only pure app launch stuff, not interface stuff
            } else {
                self.window = UIWindow()
                let vc = ViewController()
                self.window!.rootViewController = vc
                self.window!.makeKeyAndVisible()
                self.window!.backgroundColor = .red
            }
            return true
    }
}

SceneDelegate.swift

import UIKit
@available(iOS 13.0, *)
class SceneDelegate: UIResponder, UIWindowSceneDelegate {
    var window : UIWindow?
    func scene(_ scene: UIScene,
        willConnectTo session: UISceneSession,
        options connectionOptions: UIScene.ConnectionOptions) {
            if let windowScene = scene as? UIWindowScene {
                self.window = UIWindow(windowScene: windowScene) 
                let vc = ViewController()                      
                self.window!.rootViewController = vc             
                self.window!.makeKeyAndVisible()                 
                self.window!.backgroundColor = .red
            }
    }
}

ViewController.swift

import UIKit
class ViewController : UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        print("view did load")
        self.view.backgroundColor = .green
    }
}

请注意，处理其他重复项(例如应用程序激活)要简单得多，因为如果您支持窗口场景，则不会在 iOS 12 上调用应用程序委托(delegate)方法。所以问题仅限于这种情况，即您有窗口/在启动时执行的 Root View Controller 操作(例如，没有 Storyboard )。