Check if URL is valid in Swift 4 - ios

Question

How can you check to see if a URL is valid in Swift 4? I'm building a simple web browser for personal use and even though I know to enter the full URL each time I'd rather get an alert instead of the app crashing if I forget.
import UIKit
import SafariServices
class MainViewController: UIViewController {
#IBOutlet weak var urlTextField: UITextField!
#IBAction func startBrowser(_ sender: Any) {
if let url = self.urlTextField.text {
let sfViewController = SFSafariViewController(url: NSURL(string: url)! as URL)
self.present(sfViewController, animated: true, completion: nil)
}
print ("Now browsing in SFSafariViewController")
}
}
For example, if I was to type in a web address without http:// or https:// the app would crash with the error 'NSInvalidArgumentException', reason: 'The specified URL has an unsupported scheme. Only HTTP and HTTPS URLs are supported.'

Answer 1

Reading the comments on the accepted answer, I could see that you actually want to validate the URL, to check if it's valid before trying to open with Safari to prevent any crash.
You can use regex to validate the string(I created an extension, so on any string, you can check if it is a valid URL):
extension String {
func validateUrl () -> Bool {
let urlRegEx = "((?:http|https)://)?(?:www\\.)?[\\w\\d\\-_]+\\.\\w{2,3}(\\.\\w{2})?(/(?<=/)(?:[\\w\\d\\-./_]+)?)?"
return NSPredicate(format: "SELF MATCHES %#", urlRegEx).evaluate(with: self)
}
}

Answer 2

You're probably crashing because you're using the ! operator and not checking that it will work. Instead try:
#IBAction func startBrowser(_ sender: Any) {
if let urlString = self.urlTextField.text {
let url: URL?
if urlString.hasPrefix("http://") {
url = URL(string: urlString)
} else {
url = URL(string: "http://" + urlString)
}
if let url = url {
let sfViewController = SFSafariViewController(url: url)
self.present(sfViewController, animated: true, completion: nil)
print ("Now browsing in SFSafariViewController")
}
}
}
This should give you the idea of how to handle the different cases, but you probably want something more sophisticated which can deal with https and strips whitespace.