UIPopoverPresentationController显示为全窗口模式弹出窗口

Question

我有一个项目，我正在使用UIPopoverPresentationController，我想将其显示为iPhone和iPad的弹出窗口。即使在只有一个带有单个UIButton的空白Storyboard的独立项目中，以下代码也会导致生成全屏模式弹出窗口。我已经多次看到类似于此问题的问题了，但是每个人似乎都通过返回.None for adaptivePresentationStyleForPresentationController来解决它，但即使包括那个也没有为我修复它。我有一个带有以下代码的ViewController - 我缺少什么？

import UIKit

class ViewController: UIViewController, UIPopoverPresentationControllerDelegate {

@IBOutlet weak var thatButton: UIButton!

@IBAction func presentPopoverController(sender: UIButton) {
    let popVC = UIViewController() //(nibName: "CameraPopover", bundle: nil)
    popVC.view.backgroundColor = UIColor.blueColor()
    popVC.modalPresentationStyle = .Popover
    popVC.preferredContentSize = CGSize(width: 100, height: 100)
    popVC.view.layer.borderWidth = 5
    popVC.view.layer.borderColor = UIColor.blackColor().CGColor

    self.presentViewController(popVC, animated: true, completion: nil)

    let popController = popVC.popoverPresentationController
    popController!.delegate = self
}

func prepareForPopoverPresentation(popoverPresentationController: UIPopoverPresentationController) {
    popoverPresentationController.permittedArrowDirections = .Down
    popoverPresentationController.sourceView = self.thatButton
    popoverPresentationController.sourceRect = self.thatButton.frame
}

func adaptivePresentationStyleForPresentationController(controller: UIPresentationController) -> UIModalPresentationStyle {
    return .None
}

func adaptivePresentationStyleForPresentationController(controller: UIPresentationController, traitCollection: UITraitCollection) -> UIModalPresentationStyle {
    return .None
}

}