在iOS中，继续收到“在解包可选值时意外发现nil”的致命错误

Question

I run my code on Xcode and it build fine but when I tap a button to change views it crashes with this error.

var selectedAccount : ACAccount!
var tweets : NSMutableArray?
var imageCache : NSCache?
var queue : NSOperationQueue?

override func viewDidLoad() {
    super.viewDidLoad()

    self.navigationItem.title = selectedAccount.accountDescription

    queue = NSOperationQueue()
    queue!.maxConcurrentOperationCount = 4

    func retrieveTweets() {
        tweets?.removeAllObjects()

        if let account = selectedAccount {
            let requestURL = NSURL(string: "https://api.twitter.com/1.1/statuses/home_timeline.json")

            let request = SLRequest(forServiceType: SLServiceTypeTwitter, requestMethod: SLRequestMethod.GET, URL: requestURL, parameters: nil)

            request.account = account
            request.performRequestWithHandler()
                {
                    responseData, urlResponse, error in

                    if(urlResponse.statusCode == 200)
                    {
                        var jsonParseError : NSError?
                        self.tweets = NSJSONSerialization.JSONObjectWithData(responseData, options: NSJSONReadingOptions.MutableContainers, error: &jsonParseError) as? NSMutableArray
                    }

                    dispatch_async(dispatch_get_main_queue()) {
                        self.tableView.reloadData()
                    }
            }
        }
    }

}

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

override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    // #warning Potentially incomplete method implementation.
    // Return the number of sections.
    return 1
}

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

    // Return the number of rows in the section.

    if let tweetCount = self.tweets?.count {
        return tweetCount
    }
    else
    {
        return 0
    }
}

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCellWithIdentifier("TweetCell", forIndexPath: indexPath) as TweetCell

    return cell
}

When it crashes it it posts an green line over the line "self.navigationItem.title = selectedAccount.accountDescription"

I'm not sure why its saying its associated with this line.

Please help

SC

Answer 1

Make sure you remove any warning messages here.