ios - Guard中定义的变量使用后仍需要立即解包

如果(stringToURL？.isValidURL)! isValidURL的字符串扩展名:Bool 始终返回Bool，但编译器仍希望解包。

在此示例中，annotation.subtitle应该已经是URL格式的字符串，但是我想确认一下。

尝试使用在guard中定义的变量比预期的要复杂得多，因为需要进一步展开。现在，我觉得我正在编写几行代码，这些代码过于复杂，以致于无法跟上/阅读我的实现。

func mapView(_ mapView: MKMapView, annotationView view: MKAnnotationView, calloutAccessoryControlTapped control: UIControl) {
    let backupURL = URL(string: "https://www.google.com")!
    guard let currentAnnotation = view.annotation, var stringToURL = currentAnnotation.subtitle else {
        // currentAnnotation has blank subtitle.  Handle by opening up any website.
        UIApplication.shared.open(backupURL, options: [:])
        return
    }
    if (stringToURL?.isValidURL)!{
        stringToURL = stringToURL?.prependHTTPifNeeded()
        if let url = URL(string: stringToURL!){
            UIApplication.shared.open(url, options: [:])
        } else {
            UIApplication.shared.open(backupURL, options: [:])
        }
    }
}

extension String {
var isValidURL: Bool {
    let detector = try! NSDataDetector(types: NSTextCheckingResult.CheckingType.link.rawValue)
    if let match = detector.firstMatch(in: self, options: [], range: NSRange(location: 0, length: self.endIndex.encodedOffset)) {
        // it is a link, if the match covers the whole string
        return match.range.length == self.endIndex.encodedOffset
    } else {
        return false
    }
}

func prependHTTPifNeeded()-> String{
    let first4 = self.prefix(4)
    if first4 != "http" {
        return "http://" + self
    } else {
        return self
    }
}

}

该代码块正确执行。
注解。subtitle=“https://www.yahoo.com”
注解。subtitle=“www.yahoo.com”
注解。subtitle=“yahoo”

最佳答案

问题在于currentAnnotation.subtitle是String??，因为subtitle不仅是String?本身，而且还是MKAnnotation协议的可选属性。因此，简单的拆包仅可验证是否已实现可选协议subtitle，而不能验证生成的String?不是nil。您也必须拆开包装。

但是您可以执行guard var stringToURL = view.annotation?.subtitle as? String else { ... }，它将正确地解包为String:

func mapView(_ mapView: MKMapView, annotationView view: MKAnnotationView, calloutAccessoryControlTapped control: UIControl) {
    let backupURL = URL(string: "https://www.google.com”)!

    guard var stringToURL = view.annotation?.subtitle as? String else {
        UIApplication.shared.open(backupURL)
        return
    }

    if stringToURL.isValidURL {
        stringToURL = stringToURL.prependHTTPifNeeded()
        let url = URL(string: stringToURL) ?? backupURL
        UIApplication.shared.open(url)
    }
}

请注意，如果未提供任何字符串，则将打开backupURL，但是如果提供了字符串且该字符串不是有效的URL，它将不会执行任何操作。因此，也许您的意思是以下内容，如果无法打开backupURL，则会打开stringToURL:

func mapView(_ mapView: MKMapView, annotationView view: MKAnnotationView, calloutAccessoryControlTapped control: UIControl) {
    let backupURL = URL(string: "https://www.google.com")!

    guard var stringToURL = view.annotation?.subtitle as? String,
        stringToURL.isValidURL else {
            UIApplication.shared.open(backupURL)
            return
    }

    stringToURL = stringToURL.prependHTTPifNeeded()
    let url = URL(string: stringToURL) ?? backupURL
    UIApplication.shared.open(url)
}

哪里:

extension String {
    var isValidURL: Bool {
        let detector = try! NSDataDetector(types: NSTextCheckingResult.CheckingType.link.rawValue)
        let range = NSRange(startIndex..., in: self)
        return detector.firstMatch(in: self, range: range)?.range == range
    }

    func prependHTTPifNeeded() -> String{
        if prefix(4) != "http" {
            return "http://" + self
        } else {
            return self
        }
    }
}