Question

我有UITableViewController基本上是新闻Feed。我还实现了一个pull to refresh功能。但是有时候当我拉动刷新它会给我错误

'数组索引超出范围'。

我知道这意味着它试图得到的物品不存在，但你能告诉我为什么吗？这是我的代码：

override func viewDidLoad() {
    super.viewDidLoad()

    refresher = UIRefreshControl()
    refresher.attributedTitle = NSAttributedString(string: "Pull to refresh")
    refresher.addTarget(self, action: "refresh", forControlEvents: UIControlEvents.ValueChanged)
    self.tableView.addSubview(refresher)
    refresh()

    tableView.delegate = self
    tableView.dataSource = self
}

和refresh（）函数：

func refresh() {

    //get username and match with userId
    let getUser = PFUser.query()
    getUser?.findObjectsInBackgroundWithBlock({ (objects, error) -> Void in

        if let users = objects {

            //clean arrays and dictionaries so we don't get indexing error
            self.messages.removeAll(keepCapacity: true)
            self.usernames.removeAll(keepCapacity: true)

            for object in users {

                if let user = object as? PFUser {

                    //make userId = username
                    self.users[user.objectId!] = user.username!
                }
            }
        }
    })

    let getPost = PFQuery(className: "Posts")
    getPost.findObjectsInBackgroundWithBlock { (objects, error) -> Void in

        if let objects = objects {

            self.messages.removeAll(keepCapacity: true)
            self.users.removeAll(keepCapacity: true)
            self.usernames.removeAll(keepCapacity: true)

            for object in objects {

                self.messages.append(object["message"] as! String)
                self.usernames.append(self.users[object["userId"] as! String]!)

                self.tableView.reloadData()
            }
        }
    }

    self.refresher.endRefreshing()
}

Answer 1

您似乎正在移除users中的所有内容，然后尝试在getPost.findObjectsInBackgroundWithBlock中访问它。

具体而言，在self.users.removeAll(keepCapacity: true)之前调用self.usernames.append(self.users[object["userId"] as! String]!)。

另外，请注意这两个查询执行异步。您无法保证在到达第二个查询的完成块时已填充users。您很可能希望将您的两个查询重组为one compound query或嵌套它们（不推荐）。

最后，根据它的外观，您可能希望使用removeAll(keepCapacity: false)而不是使用removeAll(keepCapacity: true)保留容量。

Swift 2 + Parse：数组索引超出范围

1 个答案: