Xcode 模拟器出现白屏

Question

当我运行代码时，只显示白屏，我遇到的问题是 线程 1：“[ setValue:forUndefinedKey:]：此 class 与键 calculateButtonLabel 的键值编码不兼容。” 在 AppDelegate.swift 文件中。

起始项目在这里：https://github.com/appbrewery/BMI-Calculator-iOS13

我的 CalculateViewController 代码（第一个）：

import UIKit

class CalcualteViewController: UIViewController {

    @IBOutlet weak var heightLabel: UILabel!
    @IBOutlet weak var weightLabel: UILabel!
    @IBOutlet weak var heightSlider: UISlider!
    @IBOutlet weak var weightSlider: UISlider!
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
   var bmiValue = "0.0"

    @IBAction func heightSliderChanged(_ sender: UISlider) {
        let height = String(format: "%.2f", sender.value)
        heightLabel.text = "\(height)m"
    }
    
    @IBAction func weightSliderChanged(_ sender: UISlider) {
        let weight = String(format: "%.0f", sender.value)
        weightLabel.text = "\(weight)Kg"
    }
    
    @IBAction func calculatePressed(_ sender: UIButton) {
        let height = heightSlider.value
        let weight = weightSlider.value
        
        var bmi = weight / (pow(height, 2))
        
        bmiValue = String(format: "%.1f", bmi)
        
        performSegue(withIdentifier: "goToResult", sender: self)
    }
    
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "goToResult"{
            let destinationVC = segue.destination as! ResultViewController
            destinationVC.bmiValue = bmiValue
    }
    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        // Get the new view controller using segue.destination.
        // Pass the selected object to the new view controller.
    }
    */

}
}

我的 ResultViewController 代码（第二个）：

import UIKit

class ResultViewController: UIViewController {
    @IBOutlet weak var bmiLabel: UILabel!
    @IBOutlet weak var adviceLabel: UILabel!
    
    var bmiValue: String?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
    }
    @IBAction func recalculateButton(_ sender: UIButton) {
        self.dismiss(animated: true, completion: nil)
    }

Answer 1

在您的代码库中的某处，可能是 xib 文件或情节提要，您有对 calculateButtonLabel 的引用，但未链接到任何内容。我最好的猜测是你曾经有一个不再存在的链接到它的 IBOutlet。

您链接的 GitHub 存储库不包含对 calculateButtonLabel 的引用，它在模拟器 (Xcode 12.1) 中构建和运行良好。

Xcode 模拟器出现白屏

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