prepareForSegue nil swift

Question

尝试使用`prepareForSegue`但由于某种原因它不会被调用。我正确地命名了segue并且我在我的应用程序的其他部分使用了几乎相同的代码但是由于某种原因，当我进入下一个视图时，应用程序一直在崩溃说找到了nil。

TableViewController：

class ChartsTableViewController: UITableViewController {

    var song: NSURL!
    var player:AVPlayer!

    @IBOutlet var backButton: UIBarButtonItem!
    var songs = [PFObject]()
    var parseImage: PFFile!

    @IBOutlet var hideDislikeButton: UIButton!
    @IBOutlet var hideLikeButton: UIButton!
    @IBOutlet var segment: UISegmentedControl!


    override func viewDidLoad() {
        super.viewDidLoad()
        var stopButton = UIBarButtonItem(title: "Stop", style: .Plain, target: self, action: Selector("stopMusic"))
        self.navigationItem.rightBarButtonItem = stopButton

        var query = PFQuery(className: "Songs")
        query.orderByDescending("createdAt") //new songs
        query.limit = 100
        query.cachePolicy = kPFCachePolicyCacheThenNetwork
        query.findObjectsInBackgroundWithBlock { (objects: [AnyObject]!, error: NSError!) -> Void in
            if error == nil {

                //self.songs.removeAll(keepCapacity: false)
                for object in objects {
                    self.songs.append(object as PFObject)
                }
                self.tableView.reloadData()
            }
        }

        self.tableView.backgroundColor = UIColor.greenColor()
        self.tableView.separatorColor = UIColor.blackColor()
        Flurry.logEvent("Charts View")


    }

    func stopMusic() {
        if (isPlaying == true) {
            if (player.rate > 0) && (player.error == nil) {
                //playing
                player.pause()
            }
            isPlaying = false
        }

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }



    func objectAtIndexPath(indexPath: NSIndexPath!) -> PFObject! {
        var obj : PFObject? = nil
        if(indexPath.row < self.songs.count){
            obj = self.songs[indexPath.row] as PFObject
        }


        return obj
    }


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

    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "commentSegue" {
            if let indexPath = self.tableView.indexPathForSelectedRow() {

                let object: PFObject = songs[indexPath.row]
                println(indexPath.row)
                println(songs)
                println(object)
                (segue.destinationViewController as CommentsViewController).detailItem = object

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

        let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as TableViewCell
        cell.contentView.layer.cornerRadius = 20.0
        cell.contentView.layer.masksToBounds = true
        cell.contentView.layer.borderColor = UIColor.whiteColor().CGColor
        cell.contentView.layer.borderWidth = 8
        let objectSong: PFObject = songs[indexPath.row]
        println(objectSong)
        parseImage = objectSong.valueForKey("picture") as PFFile
        let imgURL = NSURL(string: parseImage.url)
        cell.songImage.layer.borderWidth = 1
        cell.songImage.layer.masksToBounds = false
        cell.songImage.layer.borderColor = UIColor.blackColor().CGColor
        cell.songImage.layer.cornerRadius = cell.songImage.frame.height/4
        cell.songImage.clipsToBounds = true



        cell.songImage.sd_setImageWithURL(NSURL(string: parseImage.url), placeholderImage: UIImage(named: "MeipLogo"))

        cell.songTitleLabel.text = objectSong.valueForKey("title") as? String
        cell.artistNameLabel.text = objectSong.valueForKey("artistName") as? String

        let user = PFUser.currentUser()

        return cell

    }

NextViewController：

@IBOutlet var commentsView: UITableView!
    var commentsArray = [String]()
    @IBOutlet var songImage: UIImageView!
    var songObject: PFObject!

    var detailItem: AnyObject? {
        didSet {
            // Update the view.
            self.configureView()
        }
    }


    override func viewDidLoad() {
        super.viewDidLoad()
        songObject = configureView()
        songImage.layer.borderWidth = 1
        songImage.layer.masksToBounds = false
        songImage.layer.borderColor = UIColor.blackColor().CGColor
        songImage.layer.cornerRadius = songImage.frame.height/4
        songImage.clipsToBounds = true
        println(songObject)
        let parseImage: PFFile =  songObject.valueForKey("picture") as PFFile

        songImage.image = UIImage(data: parseImage.getData())
        if songObject["comments"] != nil {

            commentsArray = songObject["comments"] as [String]
        }

        commentsView.delegate = self
        commentsView.dataSource = self
    }

    // MARK:  UITextFieldDelegate Methods
    func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return 1
    }

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

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

        if (commentsArray.count == 0) {
            cell.textLabel.text = "No Comments! Be The First One smile emoticon"
        } else {
            cell.textLabel.text = commentsArray[indexPath.row]
        }

        return cell
    }

}

Answer 1

听起来detailItem未按预期设置，因此当您在configureView中展开时会发生崩溃但值为nil。这种设计也很奇怪。我会做这样的事情：

var detailItem: AnyObject? {
    didSet {
        self.configureView()
    }
}

func configureView() -> PFObject? {
    if let song = self.detailItem as? PFObject {
        // Do something with the `song` here
        return song
    }
    return nil
}

Answer 2

在viewDidLoad中detailItem尚未设置，因此会崩溃。为什么？可能是因为prepareForSegue中的分配错误，请记录对象和indexPath。

此外，您可能希望将songObject的分配移动到configureView以及将来最终对所述对象执行的操作。从configureView或viewDidLoad拨打didSet - 两者都是常见的...