View controller origin changes every time it's presented - ios

Question

This is what my view controller should be:
This is what it is sometimes:
I want to display a view controller in the circle, however, almost every time the view controller in the circle (ResultViewController) is presented, it's place is different, though its properties doesn't change at all. Here's my code:
func openCircle(withCenter center: CGPoint, dataSource: ([Items], Int, String)){
self.addCircle(withCenter: center, dataSource: dataSource)
}
func addCircle(withCenter circleCenter: CGPoint, dataSource: ([Items], Int, String)) {
let longerSide = fmax(view.frame.size.height, view.frame.size.width)
let shorterSide = fmin(view.frame.size.height, view.frame.size.width)
let circleRadius = longerSide / 2
var resultViewOrigin = CGPoint()
var resultViewSize = CGSize()
if UIDevice.current.userInterfaceIdiom == .pad {
let rectWidth = shorterSide / 2
let rectHeight = sqrt(abs(circleRadius * circleRadius - rectWidth * rectWidth)) + view.frame.size.height - circleCenter.y
resultViewSize = CGSize(width: rectWidth, height: rectHeight)
resultViewOrigin = CGPoint(x: (view.frame.size.width - rectWidth) / 2, y: view.frame.size.height - rectHeight)
} else {
resultViewOrigin = CGPoint(x: 0.0, y: 0.0)
resultViewSize = CGSize(width: view.frame.size.width, height: view.frame.size.height)
}
let resultViewController = UIStoryboard(name: "Main", bundle: Bundle.main).instantiateViewController(withIdentifier: "ResultVC") as! ResultViewController
resultViewController.transitioningDelegate = self
resultViewController.modalPresentationStyle = .custom
resultViewController.dataSource = dataSource
resultViewController.view.frame = CGRect(origin: resultViewOrigin, size: resultViewSize)
transition.circle = UIView()
transition.startingPoint = circleCenter
transition.radius = circleRadius
transition.circle.frame = circleFrame(radius: transition.radius, center: transition.startingPoint)
present(resultViewController, animated: true)
}
It works well on the iPhone, not on the iPad, what's the problem?

Answer 1

I found the problem, it's actually a missing constraint on Regular-Regular size class caused this problem, I fixed it by adding a spacing to bottom layout guide to the part that used to get misplaced.
Thanks to everybody for your idea.

Answer 2

You can use a container view instead of presenting the view controller. You can create them programmatically or in interface builder (see Apple docs).