swift - “NSInvalidArgumentException”关闭

Question

我正在练习创建一个主要不使用 Storyboard的 UI，当我开始调试时，我的应用程序崩溃了，并给我带来了这个错误。

我尝试从 info.plist 和目标中删除“main”，但不起作用

2019-10-03 12:43:13.699871+0200 provolone[3580:115566] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Can't add self as subview'

这是 myViewController，Xcode 11.1 GM 种子 (11A1027)

import UIKit
class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
          let view = UILabel()

          view.frame = CGRect(x: 0, y: 0, width: 252, height: 60)
          view.backgroundColor = .white
          self.view = view

          view.textColor = UIColor(red: 0.33, green: 0.36, blue: 0.49, alpha: 1)
          view.font = UIFont(name: "OpenSans-Bold", size: 26)
          view.numberOfLines = 0
          view.lineBreakMode = .byWordWrapping
          let paragraphStyle = NSMutableParagraphStyle()
          paragraphStyle.lineSpacing = 0

          // Line height: 30 pt

          view.textAlignment = .center
          view.attributedText = NSMutableAttributedString(string: "Connect with people\nyou love.", attributes: [NSAttributedString.Key.paragraphStyle: paragraphStyle])

          let parent = self.view!
          parent.addSubview(view)
          view.translatesAutoresizingMaskIntoConstraints = false
          view.heightAnchor.constraint(equalToConstant: 60).isActive = true
          view.centerYAnchor.constraint(equalTo: parent.centerYAnchor, constant: 137).isActive = true
    }
}

Answer 1

问题似乎出在这一行:

self.view = view

这样，您就可以将刚刚创建的标签指定为您的 View 。如果您想将标签添加到 View 中，只需按如下所示添加即可:

self.view.addSubview(view)

为了便于阅读，我还建议您重命名标签。并且不需要创建父 View 来添加标签，除非您有在此代码片段中不清楚的原因。进行这些更改后，您的代码将如下所示:

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        let view = UILabel()

        view.frame = CGRect(x: 0, y: 0, width: 252, height: 60)
        view.backgroundColor = .white

        view.textColor = UIColor(red: 0.33, green: 0.36, blue: 0.49, alpha: 1)
        view.font = UIFont(name: "OpenSans-Bold", size: 26)
        view.numberOfLines = 0
        view.lineBreakMode = .byWordWrapping
        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.lineSpacing = 0

        // Line height: 30 pt

        view.textAlignment = .center
        view.attributedText = NSMutableAttributedString(string: "Connect with people\nyou love.", attributes: [NSAttributedString.Key.paragraphStyle: paragraphStyle])

        self.view.addSubview(view)

        view.translatesAutoresizingMaskIntoConstraints = false
               view.heightAnchor.constraint(equalToConstant: 60).isActive = true
        view.centerYAnchor.constraint(equalTo: self.view.centerYAnchor, constant: 137).isActive = true
    }
}