ios - 为什么 CollectionView 上没有显示任何内容？

Question

我有一个collectionview，并且有一个带有字符串用户名的数组，该数组连接到解析，但是当我运行程序时，collectionview不显示任何内容。我通过手动将值放入数组中对其进行了硬编码，并且它起作用了，但是一旦我从解析中检索字符串，它就不起作用了。我该如何解决这个问题？

var arrayOfFriendsNames = [String]()
var arrayOfFriendsTest: [String] = ["fire.png, fire.png, fire.png"]
override func viewDidLoad() {
    super.viewDidLoad()

    var query = PFQuery(className: "_User")
    query.findObjectsInBackgroundWithBlock({
        (objects: [AnyObject]?, error: NSError?) -> Void in
        var objectIDs = objects as! [PFObject]

        for i in 0...objectIDs.count-1{
            self.arrayOfFriendsNames.append(objectIDs[i].valueForKey("username") as! String)
            print(self.arrayOfFriendsNames)
        }
    })
 self.collectionView.reloadData()
}
 func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return arrayOfFriendsNames.count
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
    let cell: friendcellView = collectionView.dequeueReusableCellWithReuseIdentifier("friendcell", forIndexPath: indexPath) as! friendcellView


    cell.friendname.text = arrayOfFriendsNames[indexPath.row]
    cell.friendpic.image = UIImage(named: arrayOfFriendsTest[indexPath.row])
    cell.friendpic.layer.cornerRadius = cell.friendpic.frame.size.width/2;
    cell.friendpic.clipsToBounds = true

    return cell
}

Answer 1

从数据库获取数据后尝试重新加载

    query.findObjectsInBackgroundWithBlock({
        (objects: [AnyObject]?, error: NSError?) -> Void in
        var objectIDs = objects as! [PFObject]

        for i in 0...objectIDs.count-1{
            self.arrayOfFriendsNames.append(objectIDs[i].valueForKey("username") as! String)
            print(self.arrayOfFriendsNames)
        }

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

    })