exc_bad_instruction on NSJSONSerialization

Question

I'm trying to fetch data from my db but I have an exc_bad_instruction on my NSJSONSerialization.

func request(url:String, callback:(NSDictionary) -> ()){
        let nsURL = NSURL(string: url)

        let task = NSURLSession.sharedSession().dataTaskWithURL(nsURL!){
            (data, response, error) in
            //var error:NSError?
            var response:NSDictionary
            do{
                response = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) as! NSDictionary
                callback(response)
            }catch{
                print("Something went wrong!")
            }


        }
        task.resume()
    }

Do you have any idea on why it's not working? Just to let you know something, I had to use the do, try, catch since Swift 2 because it was working great before!

Answer 1

Without the full error message we're guessing regarding the precise problem, but you should guard against bad input data:

func request(url:String, callback:(NSDictionary) -> ()){
    let nsURL = NSURL(string: url)

    guard nsURL != nil else {
        print("URL not valid: \(url)")
        return
    }

    let task = NSURLSession.sharedSession().dataTaskWithURL(nsURL!){
        (data, response, error) in

        guard data != nil else {
            print("dataTaskWithURL failed: \(error)")
            return
        }

        do {
            if let response = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as? NSDictionary {
                callback(response)
            } else {
                print("JSON parsing succeeded, but cast to dictionary failed")
            }
        } catch let parseError {
            print("Something went wrong: \(parseError)")
        }
    }
    task.resume()
}

The do-try-catch catches errors, not exceptions, so you have to test for valid URL and valid NSData yourself. Also, avoid forced unwrapping of optionals (e.g. !), especially when it is a plausible runtime error (e.g. no network). Use optional binding instead.