The modalPresentationStyle of a UIAlertController with this style is UIModalPresentationPopover. You must provide location information for this popover through the alert controller's popoverPresentationController
iPhone和iPad使用UIAlertController展示ActionSheep时，展示是不一样的。
所以在iPhone上正常显示的AlertController，在iPad上显示要添加几行代码
let popover = alertVc.popoverPresentationController
if (popover != nil) {
popover?.sourceView = sender
popover?.sourceRect = sender.bounds
popover?.permittedArrowDirections = .any
}
