ios - 变量已设置但打印出 nil

Question

我正在另一个 View Controller 中设置一个变量，它在 didSet 中工作，但在 viewdidload 中它打印出 nil

View Controller 1

    let methodView = MethodViewController()
    methodView.items = itemsSelected
    presentDetail(newVC)

View Controller 2

class MethodViewController: UIViewController {

    var items: [[String: Any]]? {
        didSet {
           print(items) // PRINTS OUT ITEMS NORMALLY
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        print(items) // PRINTS OUT NIL       
    }
}

Answer 1

它返回 nil，因为您正在使用一个实例设置项目，并且当您呈现屏幕并显示您的 methodViewController 时。然后你传递一个新的实例。而是使用您用来展示 Controller 的同一实例来设置项目

override func viewDidLoad() {
    super.viewDidLoad()

// Do any additional setup after loading the view.

let methodView = StackProgramViewController() //instance 1 //your case methodView
methodView.items = itemsSelected //value is set and printed


}


@IBAction func present(_ sender: Any) {

let newVc = self.storyboard?.instantiateViewController(withIdentifier: "stack") as! StackProgramViewController //instance 2 while presenting //your case newVc

newVc.items = itemsSelected //set value here with second instance nstaead of creating methodView
present(newVc, animated: true, completion: nil)

}

希望对你有帮助