无法以编程方式向UIView添加渐变视图和UILabel

import UIKit

class GradientView: UIView {
    override class var layerClass: AnyClass {
        return CAGradientLayer.self
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        if let gradientLayer = self.layer as? CAGradientLayer {
            gradientLayer.colors = [UIColor.red.cgColor, UIColor.blue.cgColor]
            gradientLayer.startPoint = CGPoint(x: 0, y: 0)
            gradientLayer.endPoint = CGPoint(x: 0, y: 1)
        }
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
}

import UIKit

class MyView: UIView {
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        let label = UILabel(frame: CGRect(x: 0, y: 0, width: frame.width, height: frame.height))
        label.text = "Hello, World!"
        label.textAlignment = .center
        label.textColor = UIColor.black
        
        addSubview(label)
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
}