如何仅在 iOS 13.0 之前包含此 swift 声明

Posted 2023-02-23

【中文标题】如何仅在 iOS 13.0 之前包含此 swift 声明

【英文标题】：How can I include this swift declaration only before iOS 13.0

【发布时间】：2020-11-25 14:59:55

【问题描述】：

我的 AppDelegate.swift 文件中有以下声明。

var window: UIWindow?

并且我只想在部署目标设置为低于 ios 13.0 时才包含它。我看过了

@available(...)

属性，但我不认为它可以做我想做的事。本质上，我希望能够在 AppDelegate.swift 和 SceneDelegate.swift 中对我的项目进行最少的更改，从而为 iOS 12 或 iOS 13 构建我的项目。我已经使用 @available(iOS 13.0, *) 和 #available(iOS 13.0, *) 对 AppDelegate.swift 和 SceneDelegate.swift 进行了更改，但是当部署目标高于 iOS 12 时，我仍然需要能够排除这个其他声明。

这是我的 AppDelegate.swift 文件：

import UIKit
import Firebase

@main
class AppDelegate: UIResponder, UIApplicationDelegate 
    var window: UIWindow? // only include for builds < iOS 13.0
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool                           
        if #available(iOS 13.0, *) 
            // Do nothing
         else      
            window = UIWindow() // only include for builds < iOS 13.0
            window?.rootViewController = UINavigationController(rootViewController: LoginController()) // only include for builds < iOS 13.0
            window?.makeKeyAndVisible() // only include for builds < iOS 13.0      
         
        FirebaseApp.configure()
        return true
    
    // MARK: UISceneSession Lifecycle
    @available(iOS 13.0, *)
    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration 
        // Called when a new scene session is being created.
        // Use this method to select a configuration to create the new scene with.
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    
    @available(iOS 13.0, *)
    func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) 
        // Called when the user discards a scene session.
        // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
        // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
    

这是我的 SceneDelegate.swift 文件：

import UIKit

@available(iOS 13.0, *)
class SceneDelegate: UIResponder, UIWindowSceneDelegate 
    var window: UIWindow?
    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) 
        guard let scene = (scene as? UIWindowScene) else  return 
        window = UIWindow(windowScene: scene)
        window?.rootViewController = UINavigationController(rootViewController: LoginController())
        window?.makeKeyAndVisible()
    
    // ...

基本上我只想更改部署目标，并在构建过程中包含或排除适当的代码。

【参考方案1】：

var window: UIWindow? // only include for builds < iOS 13.0

不要理会声明。在 iOS 12 和之前的版本中，它将引用应用程序窗口。在 iOS 13 及更高版本上，它将为零，不会造成任何伤害。