Activity Indicator 추가하기

    private lazy var activityIndicator: UIActivityIndicatorView = {
        let activityIndicator = UIActivityIndicatorView()
        activityIndicator.frame = CGRect(x: 0, y: 0, width: 50, height: 50)
        activityIndicator.center = CGPoint(x: self.view.center.x, y: self.view.center.y - self.topbarHeight)
        activityIndicator.hidesWhenStopped = false
        activityIndicator.style = UIActivityIndicatorView.Style.medium
        activityIndicator.startAnimating()
        return activityIndicator
    }()

    private func attachActivityIndicator() {
        backgroundView.backgroundColor = UIColor.white
        self.view.addSubview(backgroundView)
        self.view.addSubview(self.activityIndicator)
    }
    
    private func detachActivityIndicator() {
        if self.activityIndicator.isAnimating {
            self.activityIndicator.stopAnimating()
        }
        self.backgroundView.removeFromSuperview()
        self.activityIndicator.removeFromSuperview()
    }