iOS 9 introduced a new way of creating Popovers on iPhone. Instead of using the UIPopoverController class we can now use the UIPopoverPresentationController.

Presenting a Popover from a Bar Button Item

We need a content View controller that's displayed inside the Popover and also need to set properties for contentSize, modalPresentationStyle and sourceView.

Action for right BarButtonItem-

 @IBAction func addEntity(_ sender: UIBarButtonItem) {
        let vc: TableViewController = self.storyboard?.instantiateViewController(withIdentifier: "TableViewController") as! TableViewController
        // Preferred Size
        vc.preferredContentSize = CGSize(width: 200, height: 200)
        vc.modalPresentationStyle = .popover
        let popover: UIPopoverPresentationController = vc.popoverPresentationController!
        popover.delegate = self
        popover.sourceView = self.view
        // RightBarItem
        popover.barButtonItem = addBarButton
        present(vc, animated: true, completion:nil)
    }

delegate Method of UIPopoverPresentationController-

extension ViewController: UIPopoverPresentationControllerDelegate {
    
    func adaptivePresentationStyle(for controller: UIPresentationController) -> UIModalPresentationStyle {
        return .none
    }
    
}

Preview

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