How to check validity of URL in Swift?

Question

Trying to make an app launch the default browser to a URL, but only if the URL entered is valid, otherwise it displays a message saying the URL is invalid.

How would

Answer 1

For swift 4 you can use:

class func verifyUrl (urlString: String?) -> Bool {
    //Check for nil
    if let urlString = urlString {
        // create NSURL instance
        if let url = URL(string: urlString) {
            // check if your application can open the NSURL instance
            return UIApplication.shared.canOpenURL(url)
        }
    }
    return false
}

Answer 2

Swift 4 elegant solution using NSDataDetector:

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.utf16.count)) {
            // it is a link, if the match covers the whole string
            return match.range.length == self.utf16.count
        } else {
            return false
        }
    }
}

Usage:

let string = "https://www.fs.blog/2017/02/naval-ravikant-reading-decision-making/"
if string.isValidURL {
    // TODO
}

Reasoning behind using NSDataDetector instead of UIApplication.shared.canOpenURL:

I needed a method that would detect whether the user provided an input that is an URL to something. In many cases, users don't include the http:// nor https:// URL scheme in the URL they type in - e.g., instead of "http://www.google.com" they would type in "www.google.com". Without the URL scheme, the UIApplication.shared.canOpenURL will fail to recognize the URL and will return false. NSDataDetector is, compared to UIApplication.shared.canOpenURL, a rather forgiving tool (as @AmitaiB mentioned in comments) - and it can detect even URLs without the http:// scheme. This way I am able to detect a URL without having to try to add the scheme everytime when testing the string.

Sidenote - SFSafariViewController can open only URLs with http:///https://. Thus, if a detected URL does not have a URL scheme specified, and you want to open the link, you will have to prepend the scheme manually.

Answer 3

Helium having to deal with various schemes:

struct UrlHelpers {
    // Prepends `http://` if scheme isn't `https?://` unless "file://"
    static func ensureScheme(_ urlString: String) -> String {
        if !(urlString.lowercased().hasPrefix("http://") || urlString.lowercased().hasPrefix("https://")) {
            return urlString.hasPrefix("file://") ? urlString : "http://" + urlString
        } else {
            return urlString
        }
    }

    // https://mathiasbynens.be/demo/url-regex
    static func isValid(urlString: String) -> Bool {
        // swiftlint:disable:next force_try
        if urlString.lowercased().hasPrefix("file:"), let url = URL.init(string: urlString) {
            return FileManager.default.fileExists(atPath:url.path)
        }

        let regex = try! NSRegularExpression(pattern: "^(https?://)[^\\s/$.?#].[^\\s]*$")
        return (regex.firstMatch(in: urlString, range: urlString.nsrange) != nil)
    }
}

Answer 4

This is for latest Swift 4, based on Doug Amos answer (for swift 3)

public static func verifyUrl (urlString: String?) -> Bool {
    //Check for nil
    if let urlString = urlString {
        // create NSURL instance
        if let url = NSURL(string: urlString) {
            // check if your application can open the NSURL instance
            return UIApplication.shared.canOpenURL(url as URL)
        }
    }
    return false
}