在这个linepopover.permittedArrowDirections =(.Up | .Down)它说“没有更多的上下文,表达的类型是ambiquous”.

这是代码示例：

if let popover = alert.popoverPresentationController
        {
        popover.sourceView = imageView
        popover.sourceRect = imageView.bounds
        popover.permittedArrowDirections = ( .Up | .Down )
        }