Variable defined in Guard still require unwrapping immediately afterwards when used - ios

Question

if (stringToURL?.isValidURL)! <-- Not sure why the complier requires optional chaining on stringToURL when it is safely declared in Guard statement. Also, string extension for isValidURL: Bool always returns Bool but compiler still wants unwrapping.
In this example, annotation.subtitle should already be string in URL format but I wanted to confirm.
Trying to use variables defined in guard becomes more convoluted than expected because further unwrapping is needed. Now I feel that I'm making a few lines of code overly complicated to follow/read with my implementations.
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
}
}
}
The code block executes properly.
annotation.subtitle = "https://www.yahoo.com" <--- yahoo opens
annotation.subtitle = "www.yahoo.com" <--- yahoo opens
annotation.subtitle = "yahoo" <--- google.com opens because we did not have a valid URL string

Answer 1

The problem is that currentAnnotation.subtitle is a String??, because subtitle is not only a String?, itself, but it is also an optional property of MKAnnotation protocol. So a simple unwrap only verifies that the optional protocol subtitle was implemented, but not that the resulting String? was not nil. You have to unwrap that, too.
But you can do guard var stringToURL = view.annotation?.subtitle as? String else { ... }, and it will be properly unwrapped to a 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)
}
}
Note, that will open the backupURL if no string is provided, but if a string was provided and wasn’t a valid URL, it won’t do anything. So perhaps you meant the following, which will open backupURL if it can’t open 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)
}
Where:
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
}
}
}