"Initializer for conditional binding must have optional type, not 'string'" 但在那种情况下还有什么？

Question

“条件绑定的初始化程序必须具有可选类型，而不是 'string'。我尝试了 sender.stringValue 和 sender.stringValue? 但 Xcode 事情又变得有趣了。（上面的属性错误消息）

        extension MapViewController: NSSearchFieldDelegate {
        override func searchFieldAction(sender: NSSearchField) {
            // Note: use defer to dismiss the search controller even if the guard returns
            defer {
            }

            guard let text = sender.stringValue.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())
                where !text.isEmpty else { return }

            let request = MKLocalSearchRequest()
            request.naturalLanguageQuery = text
            request.region = mapView.region

            let search = MKLocalSearch(request: request)
            search.startWithCompletionHandler { (response, error) in
                guard let item = response?.mapItems.first else { return }

                let annotation = item.placemark
                self.mapView.addAnnotation(annotation)
                self.mapView.showAnnotations([annotation], animated: true)
                self.mapView.selectAnnotation(annotation, animated: true)
            }
        }

Answer 1

你只要

let text = sender.stringValue.stringByTrimmingCharactersInSet(.whitespaceAndNewlineCharacterSet())

guard !text.isEmpty else { return }

"Initializer for conditional binding must have optional type, not 'string'" 但在那种情况下还有什么？

"Initializer for conditional binding must have optional type, not 'string'" but what else in that situation?

swift

macos

mapkit

appkit