Common ancestor constraints issue. This is how I solved it.

[keegho]

ERROR:

"Because they have no common ancestor. Does the constraint or its anchors reference items in different view hierarchies?"

Change the topView to a dynamic one. When user uses showProgressView function he has to pass by self.view

   `open func showProgressView(_ ancestorView: UIView) {
    
    //This is making an error
   //guard let topView = UIApplication.shared.keyWindow?.rootViewController?.view else {
   //return
   //}
    
    containerView.backgroundColor = self.backgroundColor
    progressView.backgroundColor = self.forgroundColor
    activityIndicator.style = self.activityStyle

    UIApplication.shared.keyWindow?.addSubview(containerView)
    progressView.addSubview(activityIndicator)
    containerView.addSubview(progressView)
    
    activeConstraints = [
        containerView.heightAnchor.constraint(equalTo: ancestorView.heightAnchor),
        containerView.widthAnchor.constraint(equalTo: ancestorView.widthAnchor),
        containerView.leadingAnchor.constraint(equalTo: ancestorView.leadingAnchor),
        containerView.topAnchor.constraint(equalTo: ancestorView.topAnchor),

        progressView.heightAnchor.constraint(equalToConstant: self.size.height),
        progressView.widthAnchor.constraint(equalToConstant: self.size.width),
        progressView.centerYAnchor.constraint(equalTo: containerView.centerYAnchor),
        progressView.centerXAnchor.constraint(equalTo: containerView.centerXAnchor),

        activityIndicator.heightAnchor.constraint(equalToConstant: self.size.height),
        activityIndicator.widthAnchor.constraint(equalToConstant: self.size.width),
        activityIndicator.centerYAnchor.constraint(equalTo: progressView.centerYAnchor),
        activityIndicator.centerXAnchor.constraint(equalTo: progressView.centerXAnchor)
    ]
    
    
    for constraint in activeConstraints {
        constraint.isActive = true
    }

    activityIndicator.startAnimating()

}

`