Unable to add top and centerX constraints programmatically - ios

Question

let imageView = UIImageView(image: UIImage(named: "Loading"))
imageView.frame = CGRect(x: 100, y: 100, width: 200, height: 200)
imageView.center = self.view.center
self.view.addSubview(imageView)
let xConstraint = NSLayoutConstraint(item: imageView, attribute: .centerX, relatedBy: .equal, toItem: self.view, attribute: .centerX, multiplier: 1, constant: 0)
let verticalSpace = NSLayoutConstraint(item: imageView, attribute: .top, relatedBy: .equal, toItem: self.view, attribute: .bottom, multiplier: 1, constant: 100)
NSLayoutConstraint.activate([xConstraint, verticalSpace])
self.rotate(imageView: imageView, aCircleTime: 1)
let titleLabel = UILabel()
titleLabel.text = "Loading picker route"
titleLabel.textAlignment = .center
self.view.addSubview(imageView)
NSLayoutConstraint(item: titleLabel, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: self.view.frame.size.width).isActive = true
NSLayoutConstraint(item: titleLabel, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 44).isActive = true
NSLayoutConstraint(item: titleLabel, attribute: .centerX, relatedBy: .equal, toItem: imageView , attribute: .centerX, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: titleLabel, attribute: .top, relatedBy: .equal, toItem: imageView, attribute: .bottom, multiplier: 1, constant: 100).isActive = true
Crash at last two lines with below report
Terminating app due to uncaught exception 'NSGenericException',
reason: 'Unable to activate constraint with anchors
<NSLayoutYAxisAnchor:0x2839a8540 "UILabel:0x115d12580.top"> and
<NSLayoutYAxisAnchor:0x2839fc000 "UIImageView:0x115d10730.bottom">
because they have no common ancestor. Does the constraint or its
anchors reference items in different view hierarchies? That's
illegal.'

Answer 1

You need to add the the label
titleLabel.textAlignment = .center
self.view.addSubview(titleLabel)
plus these 2 lines
imageView.translatesAutoresizingMaskIntoConstraints = false
titleLabel.translatesAutoresizingMaskIntoConstraints = false
Edit:
let imageView = UIImageView(image: UIImage(named: "Loading"))
imageView.frame = CGRect(x: 100, y: 100, width: 200, height: 200)
imageView.center = self.view.center
self.view.addSubview(imageView)
let xConstraint = NSLayoutConstraint(item: imageView, attribute: .centerX, relatedBy: .equal, toItem: self.view, attribute: .centerX, multiplier: 1, constant: 0)
let verticalSpace = NSLayoutConstraint(item: imageView, attribute: .top, relatedBy: .equal, toItem: self.view, attribute: .top, multiplier: 1, constant: 100)
let width = NSLayoutConstraint(item: imageView, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 200)
let height = NSLayoutConstraint(item: imageView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 200)
NSLayoutConstraint.activate([xConstraint, verticalSpace,width,height])
self.rotate(imageView: imageView, aCircleTime: 1)
let titleLabel = UILabel()
titleLabel.text = "Loading picker route"
titleLabel.textAlignment = .center
self.view.addSubview(titleLabel)
imageView.translatesAutoresizingMaskIntoConstraints = false
titleLabel.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint(item: titleLabel, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: self.view.frame.size.width).isActive = true
NSLayoutConstraint(item: titleLabel, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 44).isActive = true
NSLayoutConstraint(item: titleLabel, attribute: .centerX, relatedBy: .equal, toItem: imageView , attribute: .centerX, multiplier: 1, constant: 0).isActive = true
NSLayoutConstraint(item: titleLabel, attribute: .top, relatedBy: .equal, toItem: imageView, attribute: .bottom, multiplier: 1, constant: 100).isActive = true