ios - 创建一个对象的新实例并将其放入一个数组中，并使用 TabBarView 上的按钮快速

Question

我只是想创建一个标签栏 View ，上面有一个按钮，用于创建对象的实例，然后将其添加到数组中。我只使用一个 View Controller 就可以让它工作，但是由于某种原因，当我添加一个选项卡栏 Controller 时，我终生无法让它工作。现在它抛出这个错误 - fatal error :在展开可选值时意外发现 nil

这是我目前在几个不同文件中的所有代码

class ItemStore {

    var allItems = [Item]()



    @discardableResult func createItem() -> Item {
        let newItem = Item(name: "Item")

        allItems.append(newItem)

        return newItem
    }
}

这是项目，然后创建并将其添加到数组

这是我的主视图 Controller :

class ViewController: UIViewController {

    var itemStore: ItemStore

    required init?() {
    }


    @IBAction func testButton(_ sender: Any) {

        print("This is working")
        itemStore.createItem() //this is where the error gets thrown
        print("We made it")

    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        print("is this coming up")


    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

这就是我在 app delegate 中所拥有的，让我走到这一步

class AppDelegate: UIResponder, UIApplicationDelegate {

var window: UIWindow?
var itemStore = ItemStore()


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

    let tabController = window?.rootViewController as? ViewController
    tabController?.itemStore = itemStore

    return true
}

我确实有 UITabController 的文件..但它现在是空的。我已经尝试了各种各样的事情，但我想我只是还不明白。

如有任何帮助，我们将不胜感激。

Answer 1

当您尝试force-unwrap 可选变量但值不存在(nil)时，会发生上述错误。试试这个方法。

---

将 itemStore 设为 ViewController 中的可选变量

class ViewController: UIViewController {
    var itemStore: ItemStore?
}

---

并写下这一行

var itemStore = ItemStore()

在 didFinishLaunchingWithOptions 中修改函数如下

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

    var itemStore = ItemStore()

    if let tabController = window?.rootViewController as? ViewController {
      //MAKE SURE THAT THIS `IF` condition is satisfied by putting a break point here
      tabController.itemStore = itemStore
    }


    return true
}

你的函数应该是这样的

@IBAction func testButton(_ sender: Any) {

    guard let itemStore = itemStore else {
     //item store is nil. probably not initialized properly from appDelegate.
     return //be safe
    }
    //itemStore is not nil
    itemStore.createItem() //now error will not be thrown
    print("We made it")

}

如果需要帮助，请告诉我