Finding Nil When Unwrapping Optional

Question

I have a table view that gets data from an RSS feed. The table view loads with the title string for each element but when I select a row to go to the url for the selected row, it crashes due to unexpectedly finding nil while unwrapping an optional value. Also, the images aren't loading from the image URLs. I have verified that these are not nil with print statements. What am I missing? It crashes on let safariVC = SFSafariViewController(URL: url!, entersReaderIfAvailable: true)

I know for sure that every item in the table view will always have a link so force unwrapping shouldn't be an issue. Here is an example of one of the URLs: linkString: http://kyfbnewsroom.com/state-ag-department-assisted-the-farm-community-through-a-month-marked-by-challenges/ but url is nil.

Here is the complete code.

import UIKit
import SafariServices

class NewsFeedTableViewController: UITableViewController, NSXMLParserDelegate, NSURLConnectionDelegate, NSURLConnectionDataDelegate, UINavigationControllerDelegate, SFSafariViewControllerDelegate, APLSlideMenuViewControllerDelegate {

    var urlString = NSString()
    var parser = NSXMLParser()
    var posts = NSMutableArray()
    var elements = NSMutableDictionary()
    var element = NSString()
    var itemTitle = NSMutableString()
    var link = NSMutableString()
    var thumbnailURL = NSMutableString()
    var isActionAlert = false
    var attributes = NSDictionary()
    var connection: NSURLConnection?
    var xmlData: NSMutableData?

    var loadingIndicator = UIActivityIndicatorView()
    var backgroundImage = UIImage()
    var backgroundImageView = UIImageView()
    let kfbBlue = UIColor(red: 8.0 / 255.0, green: 77.0 / 255.0, blue: 139.0 / 255.0, alpha: 0.7)

    override func viewDidLoad() {
        super.viewDidLoad()

        tableView.registerNib(UINib(nibName: "NewsCell", bundle: nil), forCellReuseIdentifier: "newsCell")

        let menuButton = UIBarButtonItem(image: UIImage(named: "list_button"), style: .Done, target: self, action: "showMenu")
        self.navigationItem.leftBarButtonItem = menuButton

        let reloadButton = UIBarButtonItem(barButtonSystemItem: .Refresh, target: self, action: "reload")
        self.navigationItem.rightBarButtonItem = reloadButton

        backgroundImageView = UIImageView(image: backgroundImage)
        tableView.backgroundView = backgroundImageView

        let width = CGRectGetWidth(self.view.bounds)
        let height = CGRectGetHeight(self.view.bounds)

        loadingIndicator = UIActivityIndicatorView(frame: CGRectMake(width / 2, height / 2, 75, 75))
        loadingIndicator.layer.cornerRadius = 10
        loadingIndicator.backgroundColor = kfbBlue
        loadingIndicator.center = CGPointMake(width / 2, height / 2 - 37)
        loadingIndicator.activityIndicatorViewStyle = .WhiteLarge
        loadingIndicator.hidesWhenStopped = true
        tableView.addSubview(loadingIndicator)
        loadingIndicator.startAnimating()
    }

    override func viewDidDisappear(animated: Bool) {
        loadingIndicator.stopAnimating()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func showMenu() {
        self.slideMenuController().showLeftMenu(true)
    }

    func beginParsing() {
        posts = []
        xmlData = NSMutableData()
        let url = NSURL(string: self.urlString as String)
        let req = NSURLRequest(URL: url!)
        connection = NSURLConnection(request: req, delegate: self, startImmediately: true)!
    }

    func reload() {
        loadingIndicator.startAnimating()
        self.beginParsing()
    }

    // MARK: - NSURLConnection Methods

    func connection(connection: NSURLConnection, didReceiveData data: NSData) {
        xmlData!.appendData(data)
    }

    func connectionDidFinishLoading(connection: NSURLConnection) {
        loadingIndicator.stopAnimating()

        let effectImage = self.backgroundImage.applyDarkEffect()
        self.backgroundImageView.image = effectImage

        parser = NSXMLParser(data: self.xmlData!)
        parser.delegate = self
        parser.parse()
        xmlData = nil
        tableView.reloadData()
    }

    func connection(connection: NSURLConnection, didFailWithError error: NSError) {
        self.connection = nil
        self.xmlData = nil

        loadingIndicator.stopAnimating()

        let errorString = NSString(format: "Fetch failed: %@", error.localizedDescription)
        TSMessage.showNotificationWithTitle("Network Error", subtitle: errorString as String, type: .Error)
    }

    // MARK: - XML Parser Methods

    func parser(parser: NSXMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String]) {

        attributes = attributeDict

        element = elementName
        if ((elementName as NSString).isEqualToString("item")) {
            elements = NSMutableDictionary()
            elements = [:]
            itemTitle = NSMutableString()
            itemTitle = ""
            link = NSMutableString()
            link = ""
            thumbnailURL = NSMutableString()
            thumbnailURL = ""
        }
    }

    func parser(parser: NSXMLParser, foundCharacters string: String) {
        if (string == "Action Alert") {
            self.isActionAlert = true
        }

        if (element.isEqualToString("title")) {
            itemTitle.appendString(string)
        } else if (element.isEqualToString("link")) {
            link.appendString(string)
        } else if (element.isEqualToString("media:thumbnail")) {
            thumbnailURL.appendString(attributes.objectForKey("url") as! String)
        }
    }

    func parser(parser: NSXMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?) {
        if (!isActionAlert) {
            if ((elementName as NSString).isEqualToString("item")) {
                if !itemTitle.isEqual(nil) {
                    elements.setObject(itemTitle, forKey: "title")
                }
                if !link.isEqual(nil) {
                    elements.setObject(link, forKey: "link")
                }
                if !thumbnailURL.isEqual(nil) {
                    elements.setObject(thumbnailURL, forKey: "thumbnail")
                }

                posts.addObject(elements)
            }
        }
    }

    // MARK: - Table view data source

    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return 1
    }

    override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
        return 136
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return posts.count
    }

    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("newsCell", forIndexPath: indexPath) as! NewsCell

        cell.newsTitle?.text = posts.objectAtIndex(indexPath.row).valueForKey("title") as? String
        cell.newsTitle!.textColor = UIColor.whiteColor()
        if (UIDevice.currentDevice().userInterfaceIdiom == .Phone) {
            cell.newsTitle!.font = UIFont(name: "FranklinGothicStd-ExtraCond", size: 22.0)
        } else {
            cell.newsTitle!.font = UIFont(name: "FranklinGothicStd-ExtraCond", size: 30.0)
        }
        cell.backgroundColor = UIColor.clearColor()
        cell.selectionStyle = .None

        var thumbString = posts.objectAtIndex(indexPath.row).valueForKey("thumbnail") as? String
    thumbString = thumbString!.stringByAddingPercentEncodingWithAllowedCharacters(NSCharacterSet.URLQueryAllowedCharacterSet())
    thumbString = thumbString!.stringByReplacingOccurrencesOfString("%09%09", withString:"")
    print(String(format: "thumbString: %@", thumbString!))
    // let thumbURL = NSURL(string: (posts.objectAtIndex(indexPath.row).valueForKey("thumbnail") as? String)!)
    let thumbURL = NSURL(string: thumbString!)

        cell.newsThumb?.sd_setImageWithURL(thumbURL, placeholderImage: UIImage(named: "placeholder"))
        cell.newsThumb!.layer.cornerRadius = 45.0
        cell.newsThumb!.clipsToBounds = true
        cell.newsThumb!.layer.borderWidth = 2.0
        cell.newsThumb!.layer.borderColor = UIColor.clearColor().CGColor
        cell.newsThumb!.backgroundColor = UIColor.clearColor()

        print(posts.objectAtIndex(indexPath.row).valueForKey("title"))
        print(posts.objectAtIndex(indexPath.row).valueForKey("link"))
        print(posts.objectAtIndex(indexPath.row).valueForKey("thumbnail"))

        return cell
    }

    override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
        let linkString = posts.objectAtIndex(indexPath.row).valueForKey("link") as? String
        let url = NSURL(string: linkString!)
        let safariVC = SFSafariViewController(URL: url!, entersReaderIfAvailable: true)
        safariVC.view.tintColor = kfbBlue
        self.navigationController?.presentViewController(safariVC, animated: true, completion: nil)
    }
}

Answer 1

I got the links working by adding

linkString = linkString!.stringByAddingPercentEncodingWithAllowedCharacters(NSCharacterSet.URLQueryAllowedCharacterSet())
            linkString = linkString?.stringByReplacingOccurrencesOfString("%09%09", withString:"")

I still can't get the images to show up though, even when I do this with the image URLs. It looks like the images aren't loading because the image URL is being added to thumbString twice. thumbString: http://kyfbnewsroom.com/wp-content/uploads/2012/10/farm-to-school-150x120.jpeghttp://kyfbnewsroom.com/wp-content/uploads/2012/10/farm-to-school-150x120.jpeg

Answer 2

I some people have mentioned you're trying to make a force-unwrapping an optional value using the ! operator. But where it happens is the interesting point here. According to Apple the constructor of the NSURL init(string:):

Returns an NSURL object initialized with URLString. If the URL string was malformed, returns nil.

So when you're trying to call the following code:

let safariVC = SFSafariViewController(URL: url!, entersReaderIfAvailable: true)

For some reason url is nil, you need to use optional-binding to check it before to unwrapping the optional value, see the following code:

if let url = NSURL(string: linkString!) {
   ...do rest of your code here
}

In the above code should be better to check too the value of linkString using optional-binding before unwrapping its value too as recommend in the other answer:

 if let linkString = posts.objectAtIndex(indexPath.row).valueForKey("link") as? String, url = NSURL(string: linkString) {
      ...do rest of your code here
 }

I hope this help you.

Answer 3

This usually occurs when force-unwrapping an optional value: "optionalValue!"

Try rewriting your method with if let. e.g.

override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    if let linkString = posts.objectAtIndex(indexPath.row).valueForKey("link") as? String, url = NSURL(string: linkString) {
        let safariVC = SFSafariViewController(URL: url, entersReaderIfAvailable: true)
        safariVC.view.tintColor = kfbBlue
        self.navigationController?.presentViewController(safariVC, animated: true, completion: nil)
    }
}