User Agent change at run time

Question

I'm trying to add mobile, desktop version site functionality on my app. But the problem is that User Agent only change at once before webView loading. In my app i add to button one for Mobile and second for Desktop version site. UIWebView pick User Agent just on start.Can anyone tell me is there any way to change User Agent at run time. Thanks

 var defaultUserAgent = String()
    @IBOutlet weak var webView: UIWebView!

    @IBOutlet weak var activityIndicator: UIActivityIndicatorView!

    override func viewDidLoad() {
        super.viewDidLoad()

        let url = NSURL(string: "https://www.youtube.com")
        let request = NSURLRequest(URL: url!)
        activityIndicator.hidesWhenStopped = true
        activityIndicator.startAnimating()
        webView.loadRequest(request)
    }

    @IBAction func mobile(sender: AnyObject) {
        NSUserDefaults.standardUserDefaults().registerDefaults(["UserAgent": defaultUserAgent])
        print(defaultUserAgent)

        let url = NSURL(string: "https://www.youtube.com")
        let request = NSURLRequest(URL: url!)
        activityIndicator.hidesWhenStopped = true
        activityIndicator.startAnimating()
        webView.loadRequest(request)

    }

    @IBAction func desktop(sender: AnyObject) {

        NSUserDefaults.standardUserDefaults().registerDefaults(["UserAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.109 Safari/537.36"])

        let url = NSURL(string: "https://www.youtube.com")
        let request = NSURLRequest(URL: url!)
        activityIndicator.hidesWhenStopped = true
        activityIndicator.startAnimating()
        webView.loadRequest(request)

    }

    func webViewDidFinishLoad(webView: UIWebView) {
        activityIndicator.stopAnimating()
        print(webView.stringByEvaluatingJavaScriptFromString("navigator.userAgent"))
        defaultUserAgent = webView.stringByEvaluatingJavaScriptFromString("navigator.userAgent")!
    }

Answer 1

I recommend you to use WkWebView instead of UIWebView as it is comparatively more powerfull

WkWebView of iOS 9 has a direct API

 if #available(iOS 9, *) {
            webViewObj.customUserAgent = "customUserAgentValue"
 }