Warning from iOS "Do not add subviews directly to the visual effect view itself"

Question

I have a function below and when I link with the iOS 11 SDK, I get an error:

Do not add subviews directly to the visual effect view itself, instead add them to the -contentView.

The problem can be solved by changing

let effectView = UIVisualEffectView(effect: UIBlurEffect(style: .dark))"

to

effectView = UIView()

but the effect is not present that way. How can I keep using UIVisualEffectView instead of UIView? I want to keep the effect.

let imagePicker = UIImagePickerController()
let messageFrame = UIView()
var activityIndicator = UIActivityIndicatorView()
var strLabel = UILabel()    
let effectView = UIVisualEffectView(effect: UIBlurEffect(style: .dark))

func activityIndicator(_ title: String) {  
    strLabel.removeFromSuperview()
    activityIndicator.removeFromSuperview()
    effectView.removeFromSuperview()

    strLabel = UILabel(frame: CGRect(x: 50, y: 0, width: 160, height: 46))
    strLabel.text = title
    strLabel.font = UIFont.systemFont(ofSize: 14, weight: UIFont.Weight.medium)
    strLabel.textColor = UIColor(white: 0.9, alpha: 0.7)

    effectView.frame = CGRect(x: (view.frame.midX - strLabel.frame.width/2), y: (view.frame.midY - strLabel.frame.height/2), width: 160, height: 46)
    effectView.layer.cornerRadius = 15
    effectView.layer.masksToBounds = true

    activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: .white)
    activityIndicator.frame = CGRect(x: 0, y: 0, width: 46, height: 46)
    activityIndicator.startAnimating()

    effectView.addSubview(activityIndicator)
    effectView.addSubview(strLabel)
    view.addSubview(effectView)
}

Answer 1

Just follow what the error says and add your subviews to UIVisualEffectView's contentView.

effectView.contentView.addSubview(activityIndicator)
effectView.contentView.addSubview(strLabel)

Answer 2

Apple says that;

Depending on the desired effect, the effect may affect content layered behind the view or content added to the visual effect view’s contentView. Apply a visual effect view to an existing view and then apply a UIBlurEffect or UIVibrancyEffect object to apply a blur or vibrancy effect to the existing view. After you add the visual effect view to the view hierarchy, add any subviews to the contentView property of the visual effect view. Do not add subviews directly to the visual effect view itself.

So, as per @the4kman add your subviews to content view of visual effect view

 effectView.contentView.addSubview(activityIndicator)
 effectView.contentView.addSubview(strLabel)