SWIFT：难以在tableView中显示数据

Question

I am attempting to display data from Parse onto the following tableView controller. For some reason, the data is not displaying on the tableView (ie the rows are blank). I do not think that the data queried from Parse is being appended to the arrays. I am wondering what I'm doing wrong here.

Here's the current output:

I am using a custom prototype cell with identifier "CellTrack" class "TrackTableViewCell" and as shown below:

Here is my code in the TableViewController file:

 import UIKit
 import Parse

 class MusicPlaylistTableViewController: UITableViewController {

var usernames = [String]()
var songs = [String]()
var dates = [String]()

override func viewDidLoad() {
    super.viewDidLoad()

}

override func viewWillAppear(animated: Bool) {
    var query = PFQuery(className:"PlaylistData")

    query.findObjectsInBackgroundWithBlock { (objects: [PFObject]?, error: NSError?) -> Void in

        if error == nil {

            if let objects = objects! as? [PFObject] {

                self.usernames.removeAll()
                self.songs.removeAll()
                self.dates.removeAll()

                for object in objects {

                    let username = object["username"] as? String

                        self.usernames.append(username!)
                        print("added username")


                    let track = object["song"] as? String

                        self.songs.append(track!)


                    let date = object["createdAt"] as? String

                        self.dates.append(date!)



                    self.tableView.reloadData()
                }
            }

        } else {

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

// MARK: - Table view data source

override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    // #warning Incomplete implementation, return the number of sections
    return 1

}

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    // #warning Incomplete implementation, return the number of rows
    return usernames.count
}

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

    let cell = tableView.dequeueReusableCellWithIdentifier("CellTrack", forIndexPath: indexPath) as! TrackTableViewCell

    cell.username.text = usernames[indexPath.row]
    cell.songTitle.text = songs[indexPath.row]
    cell.CreatedOn.text = dates[indexPath.row]

    return cell
}

 }

And here is my code in the "TrackTableViewCell.swift" class:

import UIKit

class TrackTableViewCell: UITableViewCell {


@IBOutlet weak var songTitle: UILabel!

@IBOutlet weak var username: UILabel!

@IBOutlet weak var CreatedOn: UILabel!

override func awakeFromNib() {
    super.awakeFromNib()
    // Initialization code
}

override func setSelected(selected: Bool, animated: Bool) {
    super.setSelected(selected, animated: animated)

    // Configure the view for the selected state
}

}

Answer 1

Execute your tableView.reloadData() in main thread.

dispatch_async(dispatch_get_main_queue(), {
   self.tableViewCell.reloadData()
})

Answer 2

Try doing a guard let to see if those values are actually coming back as string or not. My guess would be that the value for created at never came back. Try it out and let me know.

   guard let username = object["username"] as? String else { 
   print ("could not get username") 
   }

   self.usernames.append(username)
   print("added username")

   guard let track = object["song"] as? String else {
   print ("could not get song") 
   return 
   }
   self.songs.append(track)

   guard let date = object["createdAt"] as? String else {
   print ("could not get createdAt")
   return}

   self.dates.append(date!)

Answer 3

func dequeueReusableCellWithIdentifier(_ identifier: String) -> UITableViewCell?

Return Value

A UITableViewCell object with the associated identifier or nil if no such object exists in the reusable-cell queue.

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

  var cell = tableView.dequeueReusableCellWithIdentifier("CellTrack", forIndexPath: indexPath) as! TrackTableViewCell

  if cell == nil {
    // create a new cell here
    cell = TrackTableViewCell(...)
  }

  cell.username.text = usernames[indexPath.row]
  cell.songTitle.text = songs[indexPath.row]
  cell.CreatedOn.text = dates[indexPath.row]

  return cell
}