检索远程 JSON 数据后，Swift 3/iOS UIView 未更新

Question

我有一个带有用户列表的UITableView。当您点击一行时，用户的 uid 将传递给 UIViewController 详细信息视图。使用URLRequest 检索用户的JSON 数据（用户名、头像等）。但是，详细视图会不一致地更新信息。有时它会显示用户的姓名、头像等，但有时它什么也不显示，或者只显示用户名或只显示头像等。

在fetchUser() 方法中，我有一个print("Username: \(self.user.username)")，它显示100% 的时间正在检索正确的数据，但它不会在视图中100% 的时间显示它。

任何帮助将不胜感激。

谢谢！

class ProfileViewController: UIViewController {

    @IBOutlet weak var avatarImageView: UIImageView!
    @IBOutlet weak var usernameLabel: UILabel!
    @IBOutlet weak var networthLabel: UILabel!

    var user: User!
    var uid: Int?

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
        fetchUser()
    }

    func reloadView() {
        self.usernameLabel.text = user.username
        self.networthLabel.text = "$" + NumberFormatter.localizedString(from: Int((user.networth)!)! as NSNumber, number: NumberFormatter.Style.decimal)
        self.avatarImageView.downloadImage(from: user.avatar!)
        circularImage(photoImageView: self.avatarImageView)
    }

    func fetchUser() {
        // Post user data to server
        let myUrl = NSURL(string: "http://localhost/test/profile")
        let urlRequest = NSMutableURLRequest(url: myUrl! as URL);
        urlRequest.httpMethod = "POST"

        let postString = "uid=\(uid!)"

        urlRequest.httpBody = postString.data(using: String.Encoding.utf8)

        let task = URLSession.shared.dataTask(with: urlRequest as URLRequest) { (data, response, error) in

            if (error != nil) {
                print("error=\(String(describing: error))")
                return
            } // end if

            self.user = User()

            do {

                let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? [String : AnyObject]

                if let parseJSON = json?["data"] as? [[String : AnyObject]] {

                    for userFromJson in parseJSON {

                        let userData = User()

                        if let uid = userFromJson["uid"] as? String,
                            let username = userFromJson["username"] as? String,
                            let networth = userFromJson["networth"] as? String,
                            let avatar = userFromJson["avatar"] as? String {

                            userData.uid = Int(uid)
                            userData.username = username
                            userData.networth = networth
                            userData.avatar = avatar

                            self.usernameLabel.text = username
                            self.networthLabel.text = networth
                            self.avatarImageView.downloadImage(from: avatar)
                            circularImage(photoImageView: self.avatarImageView)

                        } // end if

                        self.user = userData

                    } // end for

                } // end if

                DispatchQueue.main.async {
                    print("Username: \(self.user.username)")
                    self.reloadView()
                }

            } catch let error {
                print(error)
            }
        }
        task.resume()

    }

Answer 1

首先，像这样在viewWillAppear 中调用fetch user：

override func viewWillAppear(_ animated: Bool) { super.viewWillAppear(animated) fetchUser() }

然后，像我一样更改此处的代码，不要使用您拥有的reloadView 函数，而是在fetchUser 函数的末尾更新主线程上的UI 元素。我还对其进行了更改，因此您不会两次更新 UI，因为您在 fetchUser 中的 if let uid = ... 语句的底部有 4 行更新了不在主线程中的 UI 元素，这就是为什么在我的版本中我删除了那 4 行代码。如果这对你有用，请告诉我。

let task = URLSession.shared.dataTask(with: urlRequest as URLRequest) { (data, response, error) in

        if (error != nil) {
            print("error=\(String(describing: error))")
            return
        } // end if

        self.user = User()

        do {

            let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? [String : AnyObject]

            if let parseJSON = json?["data"] as? [[String : AnyObject]] {

                for userFromJson in parseJSON {

                    let userData = User()

                    if let uid = userFromJson["uid"] as? String,
                        let username = userFromJson["username"] as? String,
                        let networth = userFromJson["networth"] as? String,
                        let avatar = userFromJson["avatar"] as? String {

                        userData.uid = Int(uid)
                        userData.username = username
                        userData.networth = networth
                        userData.avatar = avatar

                    } // end if

                    self.user = userData

                } // end for

            } // end if

            DispatchQueue.main.async {
                self.usernameLabel.text = user.username
                self.networthLabel.text = "$" + NumberFormatter.localizedString(from: Int((user.networth)!)! as NSNumber, number: NumberFormatter.Style.decimal)
                self.avatarImageView.downloadImage(from: user.avatar!)
                circularImage(photoImageView: self.avatarImageView)
            }

        } catch let error {
            print(error)
        }
    }
    task.resume()

Answer 2

两个建议：

1. 严格来说，所有对UIView 对象的访问都应该在主线程上。您正在调度到主线程以调用 reloadView，但当您在标签上设置“用户名”和“净值”值时也应该这样做
2. 您确定标签是空白的吗？可能是自动布局问题吗？ （尝试将标签的背景颜色设置为黄色，以检查它们的大小是否正确。有时，如果存在冲突的约束，自动布局可以将视图压缩为空）