在 iOS 应用程序上显示计算错误的错误

Question

我正在创建 iOS 响应输入变量的应用程序。

但是，打印结果时出现一条错误消息，我不知道如何修复错误。

第一条错误消息

        let result = x + y
        label.text = "result is \(result) "

Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value

我尝试做的事情

收到第一条评论后，我仔细检查了 ResultViewController.swift 并更改了转换页面。

我需要的是显示 result is 2 而不是 res... 我该如何解决？

ViewController.swift

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        // aquire ResultViewController from segue
        let resultViewController:ResultViewController = segue.destination as! ResultViewController
        // set numbers
        resultViewController.x = 1
        resultViewController.y = 1
    }

    @IBAction func unwind(_ segue: UIStoryboardSegue) {
        // called after returning back from segue 
    }
}

结果ViewController.swift

import UIKit

class ResultViewController: UIViewController {

    @IBOutlet weak var label: UILabel!

    var x:Int = 0
    var y:Int = 0

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.

        let result = x + y
        label.text = "result is \(result) "
    }
}

Answer 1

通过情节提要或编程方式在您的标签上添加约束条件

 override func viewDidLoad() {
         super.viewDidLoad()

            label.translatesAutoresizingMaskIntoConstraints = false
            label.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
            label.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
            label.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
            label.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true

            let result = x + y
            label.text = "result is \(result) "
        }

或您想在标签上添加的任何限制条件

在 iOS 应用程序上显示计算错误的错误

Error to show the calculation error on iOS app

ios

swift

xcode

xcode11