Why my subviews are getting centered , not position (0 , 0) - ios

Question

I am working on a project where Im trying to present a dialog aligned to bottom of sourceView. But while Im adding the subview to my sourceView , the view not maintaining the position to bottom alignment. I used autoresizing mask to align bottom. But not working.
Here is my code :
func presentDialogViewControllerFromBottom(_ dialogViewController: UIViewController, animationPattern: LSAnimationPattern = .fadeInOut, backgroundViewType: LSDialogBackgroundViewType = .solid, dismissButtonEnabled: Bool = true, completion: (() -> Swift.Void)? = nil) {
// get the view of viewController that called the dialog
let sourceView = self.getSourceView()
self.ls_dialogViewController = dialogViewController
sourceView.tag = LSSourceViewTag
// dialog View
let dialogView: UIView = ls_dialogViewController!.view
dialogView.autoresizingMask = [ .flexibleLeftMargin, .flexibleTopMargin, .flexibleRightMargin]
dialogView.alpha = 0.0
dialogView.tag = LSDialogViewTag
if sourceView.subviews.contains(dialogView) {
return
}
let overlayView: UIView = UIView(frame: sourceView.bounds)
overlayView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
overlayView.backgroundColor = .clear
overlayView.tag = LSOverlayViewTag
// background View
self.ls_dialogBackgroundView = LSDialogBackgroundView(frame: sourceView.bounds)
self.ls_dialogBackgroundView!.autoresizingMask = [.flexibleWidth, .flexibleHeight]
self.ls_dialogBackgroundView!.backgroundColor = .clear
self.ls_dialogBackgroundView!.backgroundViewType = backgroundViewType
self.ls_dialogBackgroundView!.alpha = 0.0
if let _ = self.ls_dialogBackgroundView {
overlayView.addSubview(self.ls_dialogBackgroundView!)
}
// dismiss button
let dismissButton = UIButton(type: .custom)
dismissButton.autoresizingMask = [.flexibleWidth, .flexibleHeight]
dismissButton.backgroundColor = .clear
dismissButton.frame = sourceView.bounds
dismissButton.tag = animationPattern == LSAnimationPattern.fadeInOut ? LSAnimationPattern.fadeInOut.rawValue : animationPattern.rawValue
dismissButton.addTarget(self, action: #selector(self.tapLSDialogBackgroundView(_:)), for: .touchUpInside)
dismissButton.isEnabled = dismissButtonEnabled
// add view
overlayView.addSubview(dismissButton)
overlayView.addSubview(dialogView)
sourceView.addSubview(overlayView)
// set animation pattern and call
LSAnimationUtils.shared.startAnimation(self, dialogView: dialogView, sourceView: sourceView, overlayView: overlayView, animationPattern: animationPattern)
// called after the dialog display
completion?()
}