无法添加填充的约束

我正在开发一个自定义控件,它最终将成为一个按钮。我已经成功地在界面生成器中构建了设计,但当我试图以编程方式构建相同的视图时,它并没有按预期工作。我试图通过在将标签连接到其超视图的约束上设置常量来强制进行一些填充,但是,这并没有按预期工作。

class RoundedButton3: UIView {

var stringLabel: UILabel
var numberLabel: UILabel
var leftBackground: UIView
var rightBackground: UIView
var stackView: UIStackView

override init(frame: CGRect) {
    stringLabel = UILabel()
    numberLabel = UILabel()
    leftBackground = UIView()
    rightBackground = UIView()
    stackView = UIStackView()
    super.init(frame: frame)

    self.contentMode = .scaleToFill
    self.autoresizingMask = [.flexibleBottomMargin, .flexibleTopMargin, .flexibleLeftMargin, .flexibleRightMargin]

    self.translatesAutoresizingMaskIntoConstraints = false

    stringLabel.translatesAutoresizingMaskIntoConstraints = false
    numberLabel.translatesAutoresizingMaskIntoConstraints = false
    leftBackground.translatesAutoresizingMaskIntoConstraints = false
    rightBackground.translatesAutoresizingMaskIntoConstraints = false
    stackView.translatesAutoresizingMaskIntoConstraints = false


    self.addSubview(stackView)
    leftBackground.addSubview(stringLabel)
    rightBackground.addSubview(numberLabel)
    stackView.addArrangedSubview(leftBackground)
    stackView.addArrangedSubview(rightBackground)

    stackView.axis = .horizontal
    stackView.alignment = .fill
    stackView.distribution = .fill

    stringLabel.setContentHuggingPriority(UILayoutPriorityRequired, for: .horizontal)
    stringLabel.setContentHuggingPriority(UILayoutPriorityRequired, for: .vertical)
    stringLabel.setContentCompressionResistancePriority(UILayoutPriorityRequired, for: .horizontal)
    stringLabel.setContentCompressionResistancePriority(UILayoutPriorityRequired, for: .vertical)
    numberLabel.setContentHuggingPriority(UILayoutPriorityRequired, for: .horizontal)
    numberLabel.setContentHuggingPriority(UILayoutPriorityRequired, for: .vertical)
    numberLabel.setContentCompressionResistancePriority(UILayoutPriorityRequired, for: .horizontal)
    numberLabel.setContentCompressionResistancePriority(UILayoutPriorityRequired, for: .vertical)

    self.topAnchor.constraint(equalTo: stackView.topAnchor).isActive = true
    self.bottomAnchor.constraint(equalTo: stackView.bottomAnchor).isActive = true
    self.rightAnchor.constraint(equalTo: stackView.rightAnchor).isActive = true
    self.leftAnchor.constraint(equalTo: stackView.leftAnchor).isActive = true

    leftBackground.leftAnchor.constraint(equalTo: stringLabel.leftAnchor, constant: 4).isActive = true
    leftBackground.rightAnchor.constraint(equalTo: stringLabel.rightAnchor, constant: 4).isActive = true
    leftBackground.topAnchor.constraint(equalTo: stringLabel.topAnchor, constant: 4).isActive = true
    leftBackground.bottomAnchor.constraint(equalTo: stringLabel.bottomAnchor, constant: 4).isActive = true

    rightBackground.leftAnchor.constraint(equalTo: numberLabel.leftAnchor, constant: 4).isActive = true
    rightBackground.rightAnchor.constraint(equalTo: numberLabel.rightAnchor, constant: 4).isActive = true
    rightBackground.topAnchor.constraint(equalTo: numberLabel.topAnchor, constant: 4).isActive = true
    rightBackground.bottomAnchor.constraint(equalTo: numberLabel.bottomAnchor, constant: 4).isActive = true

    stringLabel.text = "RESERVE"
    numberLabel.text = "10"

    stringLabel.textColor = AppColors.WSF_GREEN
    numberLabel.textColor = UIColor.white
    rightBackground.backgroundColor = AppColors.WSF_GREEN
    leftBackground.backgroundColor = UIColor.white
    self.layer.borderColor = AppColors.WSF_GREEN.cgColor
    self.layer.borderWidth = 3
    self.layer.cornerRadius = 4
    self.layer.masksToBounds = true
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}

}