Swift prepareForSegue object is nil

Question

I'm trying to pass the event Object into DetailViewController, but it crashes and says: "fatal error: unexpectedly found nil while unwrapping an Optional value". I'm positive the error is in my prepare(for segue:) function, but I've been at this for hours and I can't find out how to fix it. Any help would be appreciated. Thanks!

Here is my code:

class MainViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {

@IBOutlet weak var textView: UITextView!
@IBOutlet weak var tableView: UITableView!

var events = [Event]()

override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.


    tableView.delegate = self
    tableView.dataSource = self

    parseCSV()
}

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


@IBAction func logOutAction(sender: AnyObject) {
    if FIRAuth.auth()?.currentUser != nil {
        do {
            try FIRAuth.auth()?.signOut()
            let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "SignUp")
            present(vc, animated: true, completion: nil)

        } catch let error as NSError {
            print(error.localizedDescription)
        }
    }
}

func parseCSV() {
    let path = Bundle.main.path(forResource: "eventData", ofType: "csv")
    do {
        let csv = try CSV(contentsOfURL: path!)
        let rows = csv.rows

        for row in rows {
            let eventTitle = row["Title "]!
            let eventLoc = row[" Location "]!
            let eventStart = row[" Start_Time "]!
            let eventEnd = row [" End_Time"]!

            let event = Event(title: eventTitle, loc: eventLoc, start: eventStart, end: eventEnd)
            events.append(event)
        }
    } catch let err as NSError {
        print(err.debugDescription)
    }
}


func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    if let cell = tableView.dequeueReusableCell(withIdentifier: "eventCell", for: indexPath) as? EventCell{
        let event = events[indexPath.row]
        cell.updateUI(event: event)

        return cell
    } else {
        return UITableViewCell()
    }
}

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

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let event = events[indexPath.row]
    performSegue(withIdentifier: "detailSegue", sender: event)
}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "detailSeque" {
        if let detailVC = segue.destination as? DetailViewController {
            if let event = sender as? Event {
                detailVC.event = event
            }
        }
    }
}
}

My DetailViewController class:

class DetailViewController: UIViewController {

var event: Event!

@IBOutlet weak var eventTitle: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()

    eventTitle.text = event.title // error here. says event is nil.
    }
}

Answer 1

Since the segue is connected from your cell, it already performed automatically when you tap the cell. Performing it programmatically is resulting in your segue being performed twice: once with the value passed correctly and once without.

You can either change your segue to be connected from the view controller instead of the cell in which case your current code would work, or update your code to do all of the logic in prepareForSegue and remove your implementation of didSelectRowAt:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "detailSeque" {
        if let detailVC = segue.destination as? DetailViewController {
           let row = tableView.indexPathForSelectedRow!.row
           detailVC.event = events[row]
        }
    }
}