如果您的代码库同时支持iPhone和iPad设备，请考虑以下内容

在以下情况下定期使用present(_ viewcontrollertoppresent:animated:completion:)

呈现一个preferredStyle为.alert的UIAlertController 用.modalPresentationStyle表示一个UIViewController: .overFullScreen .formSheet .automatic未指定modalPresentationStyle时的默认值 .currentContext .fullScreen .custom .overCurrentContext

在呈现前配置popoverPresentationController的sourceRect和sourceView:

Presenting a UIAlertController with preferredStyle of .actionSheet Presenting a UIViewController with .modalPresentationStyle of: .popover .none This will crash on both iPhone and iPads with the error "The specified modal presentation style doesn't have a corresponding presentation controller." Presenting a UIActivityViewController (Based on https://developer.apple.com/documentation/uikit/uiactivityviewcontroller ; "On iPad, you must present the view controller in a popover. On iPhone and iPod touch, you must present it modally.")

下面是一个配置popoverPresentationController的例子

if let popoverController = popoverPresentationController {
  popoverController.sourceView = view
  popoverController.sourceRect = CGRect(x: view.bounds.maxX, y: 40, width: 0, height: 0)
}

如果你发现这里没有列出的其他案例，请告诉我!

Swift 3.0及更高版本更新

    let actionSheetController: UIAlertController = UIAlertController(title: "SomeTitle", message: nil, preferredStyle: .actionSheet)

    let editAction: UIAlertAction = UIAlertAction(title: "Edit Details", style: .default) { action -> Void in

        print("Edit Details")
    }

    let deleteAction: UIAlertAction = UIAlertAction(title: "Delete Item", style: .default) { action -> Void in

        print("Delete Item")
    }

    let cancelAction: UIAlertAction = UIAlertAction(title: "Cancel", style: .cancel) { action -> Void in }

    actionSheetController.addAction(editAction)
    actionSheetController.addAction(deleteAction)
    actionSheetController.addAction(cancelAction)

//        present(actionSheetController, animated: true, completion: nil)   // doesn't work for iPad

    actionSheetController.popoverPresentationController?.sourceView = yourSourceViewName // works for both iPhone & iPad

    present(actionSheetController, animated: true) {
        print("option menu presented")
    }

在Swift 2中，你想要在iPhone和iPad上正确地显示它:

func confirmAndDelete(sender: AnyObject) {
    guard let button = sender as? UIView else {
        return
    }

    let alert = UIAlertController(title: NSLocalizedString("Delete Contact?", comment: ""), message: NSLocalizedString("This action will delete all downloaded audio files.", comment: ""), preferredStyle: .ActionSheet)
    alert.modalPresentationStyle = .Popover

    let action = UIAlertAction(title: NSLocalizedString("Delete", comment: ""), style: .Destructive) { action in
        EarPlaySDK.deleteAllResources()
    }
    let cancel = UIAlertAction(title: NSLocalizedString("Cancel", comment: ""), style: .Cancel) { action in

    }
    alert.addAction(cancel)
    alert.addAction(action)

    if let presenter = alert.popoverPresentationController {
        presenter.sourceView = button
        presenter.sourceRect = button.bounds
    }
    presentViewController(alert, animated: true, completion: nil)
}

如果你不设置演示器，你将在iPad上出现一个异常-[UIPopoverPresentationController presentationTransitionWillBegin]，并显示以下消息:

Fatal Exception: NSGenericException Your application has presented a UIAlertController (<UIAlertController: 0x17858a00>) of style UIAlertControllerStyleActionSheet. The modalPresentationStyle of a UIAlertController with this style is UIModalPresentationPopover. You must provide location information for this popover through the alert controller's popoverPresentationController. You must provide either a sourceView and sourceRect or a barButtonItem. If this information is not known when you present the alert controller, you may provide it in the UIPopoverPresentationControllerDelegate method -prepareForPopoverPresentation.

只需添加以下代码在呈现您的动作表:

if let popoverController = optionMenu.popoverPresentationController {
    popoverController.sourceView = self.view
    popoverController.sourceRect = CGRect(x: self.view.bounds.midX, y: self.view.bounds.midY, width: 0, height: 0)
    popoverController.permittedArrowDirections = []
}

你可以通过使用UIPopoverPresentationController从弹窗中呈现一个UIAlertController。

在Obj-C:

UIViewController *self; // code assumes you're in a view controller
UIButton *button; // the button you want to show the popup sheet from

UIAlertController *alertController;
UIAlertAction *destroyAction;
UIAlertAction *otherAction;

alertController = [UIAlertController alertControllerWithTitle:nil
                                                      message:nil
                           preferredStyle:UIAlertControllerStyleActionSheet];
destroyAction = [UIAlertAction actionWithTitle:@"Remove All Data"
                                         style:UIAlertActionStyleDestructive
                                       handler:^(UIAlertAction *action) {
                                           // do destructive stuff here
                                       }];
otherAction = [UIAlertAction actionWithTitle:@"Blah"
                                       style:UIAlertActionStyleDefault
                                     handler:^(UIAlertAction *action) {
                                         // do something here
                                     }];
// note: you can control the order buttons are shown, unlike UIActionSheet
[alertController addAction:destroyAction];
[alertController addAction:otherAction];
[alertController setModalPresentationStyle:UIModalPresentationPopover];

UIPopoverPresentationController *popPresenter = [alertController 
                                              popoverPresentationController];
popPresenter.sourceView = button;
popPresenter.sourceRect = button.bounds;
[self presentViewController:alertController animated:YES completion:nil];

Swift 4.2的编辑，虽然有很多博客可用，但它可以节省你的时间去搜索他们。

if let popoverController = yourAlert.popoverPresentationController {
    popoverController.sourceView = self.view //to set the source of your alert
    popoverController.sourceRect = CGRect(x: self.view.bounds.midX, y: self.view.bounds.midY, width: 0, height: 0) // you can set this as per your requirement.
    popoverController.permittedArrowDirections = [] //to hide the arrow of any particular direction
}

斯威夫特5

适用于iPad和iPhone。

动作表下方悬停一个按钮

对于iPhone，动作表将显示正常，iPad将显示在按钮下方。

actionSheet.popoverPresentationController?.sourceView = fooButton
actionSheet.popoverPresentationController?.sourceRect = fooButton.bounds

动作表在屏幕/视图的中间

对于iPhone，动作表将正常显示，iPad将显示在屏幕/视图的中间。

actionSheet.popoverPresentationController?.sourceView = view
actionSheet.popoverPresentationController?.sourceRect = CGRect(x: view.bounds.midX, y: view.bounds.midY, width: 0, height: 0)
actionSheet.popoverPresentationController?.permittedArrowDirections = []