progressview.swift

func updateProgress(_ progress: Float) {
    if self.progressView == nil {
        let progressView = UIView()
        progressView.backgroundColor = .black
        progressView.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(progressView)
        let trailingConstraint =
        progressView.leadingAnchor.constraint(equalTo: self.leadingAnchor)
        NSLayoutConstraint.activate([
            progressView.topAnchor.constraint(equalTo: self.topAnchor),
            progressView.bottomAnchor.constraint(equalTo: self.bottomAnchor),
            progressView.widthAnchor.constraint(equalToConstant: 1.0),
            trailingConstraint
        ])

        self.progressView = progressView
        self.progressViewTrailingConstraint = trailingConstraint
    } else if let trailingConstraint = self.progressViewTrailingConstraint {
        let offset = self.bounds.width * CGFloat(progress)
        trailingConstraint.constant = offset
    }
}