Question

在展开del UIlabel时出现错误

@IBOutlet weak var del: UILabel! //我的标签必须通过协议实现更改

del.text = name //错误在这里

意外发现nil，同时隐式展开一个可选值

ViewController.swift

class ViewController: UIViewController,DataPass {

    @IBOutlet weak var del: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func seconeView(_ sender: UIButton) {
        let selview = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")as!SecondViewController
        present(selview,animated: true,completion: nil)

    }

    func pass(name: String) {
            del.text = name // error here Unexpectedly found nil while implicitly unwrapping an Optional value
    }
}

SecondViewController.swift

protocol DataPass {
    func pass(name:String)
}
class SecondViewController: UIViewController {

    let delegate:DataPass! = ViewController()
    let label = "Delegate"
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }


    @IBAction func endView(_ sender: UIButton) {
        if let del = delegate {
                del.pass(name: label)
        } else {
            print("Delegate property is not set")
        }
        dismiss(animated: true, completion: nil)
    }
}

Answer 1

要使您的delegate正常运行，您只需要做一些更改：

在第二个控制器中进行以下更改：

protocol DataPass {
    func pass(name:String)
}

class SecondViewController: UIViewController {

    var delegate:DataPass?
    let label = "Delegate"
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    @IBAction func endView(_ sender: UIButton) {
        if let del = delegate {
            del.pass(name: label)
        } else {
            print("Delegate property is not set")
        }
        dismiss(animated: true, completion: nil)
    }

}

并在第一个控制器中：

class ViewController: UIViewController,DataPass {

    @IBOutlet weak var del: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func seconeView(_ sender: UIButton) {
        let selview = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")as!SecondViewController
        selview.delegate = self
        present(selview,animated: true,completion: nil)
    }

    func pass(name: String) {
          del.text = name 
    }
}

说明：

在这一行let delegate:DataPass! = ViewController()中，您将为不包含任何标签的委托变量创建another instance。您需要在展示下一个控制器以使其正常工作的同时分配ViewController's instance。

在实现代理和协议时展开UILabel错误

1 个答案: