Swift Programmatic Constraint not working - ios

Question

I am trying to create a uiview that has a segment control inside. I want to be able to add this uiview to my viewcontroller's view. the segment control should be right on top of my tableview. but everytime i setup the constraints i keep getting this error
"Thread 1: Exception: "Unable to activate constraint with anchors <NSLayoutYAxisAnchor:0x282ee24c0 "UIView:0x119d3a610.bottom"> and <NSLayoutYAxisAnchor:0x282ee2500 "UITableView:0x11a014a00.top"> because they have no common ancestor. Does the constraint or its anchors reference items in different view hierarchies? That's illegal."" I tried working around by adding the subview first and what not but it's not working. here's my code if anyone can help me.
func configureTableView(){
setupSegmentControl()
view.addSubview(tableView)
setTableViewDelegates()
tableView.rowHeight = 50
tableView.translatesAutoresizingMaskIntoConstraints = false
tableView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
tableView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true
tableView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
self.tableView.topAnchor.constraint(equalToSystemSpacingBelow: self.view.topAnchor, multiplier: 20).isActive = true
tableView.register(UINib(nibName: "CustomCellNSB2", bundle: nil), forCellReuseIdentifier: "CustomCellNSB2")
}
func setTableViewDelegates(){
tableView.delegate = self
tableView.dataSource = self
}
func setupSegmentControl(){
var headerView = UIView()
var importanceSegmentControl = CustomSegmentControl()
headerView.addSubview(importanceSegmentControl)
self.view.addSubview(headerView)
importanceSegmentControl.addTarget(self, action: #selector(indexChanged(control:)),for: UIControl.Event.valueChanged)
headerView.translatesAutoresizingMaskIntoConstraints = false
headerView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor, constant: 20).isActive = true
headerView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor, constant: -20).isActive = true
headerView.bottomAnchor.constraint(equalTo: self.tableView.topAnchor, constant: 20).isActive = true
headerView.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 10).isActive = true
importanceSegmentControl.translatesAutoresizingMaskIntoConstraints = false
importanceSegmentControl.leadingAnchor.constraint(equalTo: headerView.leadingAnchor, constant: 20).isActive = true
importanceSegmentControl.trailingAnchor.constraint(equalTo: headerView.trailingAnchor, constant: -20).isActive = true
importanceSegmentControl.bottomAnchor.constraint(equalTo: headerView.topAnchor, constant: 20).isActive = true
importanceSegmentControl.topAnchor.constraint(equalTo: headerView.topAnchor, constant: 10).isActive = true
}

Answer 1

The tableView and importanceSegmentControl doesn't have any common ancestor at the time of adding the constraint to the importanceSegmentControl. So to fix the issue just switch the order of execution:
func configureTableView(){
view.addSubview(tableView)
setupSegmentControl()
//...
}