UIScrollView scroll target view to centre

UIScrollView.swift

extension UIScrollView {
	func scrollToCenter(_ targetView: UIView) {
		let viewportHeight = self.frame.height - self.contentInset.bottom
		let posInViewport = targetView.frame.origin.y + (targetView.frame.height / 2) - self.contentOffset.y
		let posDelta = (viewportHeight / 2) - posInViewport
		var newYOffset = self.contentOffset.y - posDelta

		if newYOffset < 0 {
			newYOffset = 0
		} else if newYOffset > self.subviews[0].frame.height - viewportHeight {
			newYOffset = self.subviews[0].frame.height - viewportHeight
		}

		self.setContentOffset(CGPoint(x: self.contentOffset.x, y: newYOffset), animated: true)
	}
}