如果一个对象在 appDelegate 中被实例化，它会永远存在吗？

Question

我正在学习一个教程，该教程使用作者所说的称为反向依赖注入的术语。基本上它是一个待办事项列表应用程序，它可以实例化一个 ItemStore 对象，该对象跟踪所有待办事项、重新排列等。在本教程中，我们实例化了 AppDelegate 中的 ItemStore 对象，该对象在 UITableViewController 中通过展开的属性的 UITableViewController。我的问题是，如果 ItemStore 对象在 AppDelegate 中实例化，它是否存在于应用程序的整个生命周期中？如果是这样的话，因为它不是单例，这是否意味着每次我在应用程序中显示 UITableViewController 都会造成内存泄漏或保留周期？

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.

        //create an ItemStore
        let itemStore = ItemStore()

        //now access the ItemsViewController and set its item store
        let itemsController = window!.rootViewController as! ItemsTableViewController
        itemsController.itemStore = itemStore
        //we just set the itemStore property of the ItemsTableViewController!  Yayy, WHEW!! Now when the ItemsTableViewController is accessed with that unwrapped ItemStore object then it will be set!!! WHHHHEEEEWWWWW!
        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

@Joakim 已经给出了很好的答案。如果 class 声明为 class attribute，我们可以从任何 class 访问 variable。 AppDelegate class 有一个 singleton 对象。我们可以通过这种方式访问它。

let appDelegate = UIApplication.shared.delegate as! AppDelegate
let aVariable = appDelegate.someVariable

所以它总是 returns 具有相同数据的相同对象，您可以从任何您想要的 class 访问它，但是方法中的变量只能通过此方法访问。

如果一个对象在 appDelegate 中被实例化，它会永远存在吗？

If an object is instantiated in the appDelegate does it live forever?

dependency-injection

ios

appdelegate