SWIFT - 如何解决回调发生得太晚

Question

我正在进行网络调用，获取数据并希望通过向 tableVC 中的 var 提供数据来将该数据用于 tableVC。我遇到的问题是我的回调返回数据太晚了。下面是我的代码。非常感谢任何建议

来自网络管理员的代码

  func getArticles(completion: @escaping PListCompletion) {

        guard let url = plistUrlString else { return }
        let urlRequest = URLRequest(url: url)
        let defaultConfig = URLSessionConfiguration.default
        let session = URLSession(configuration: defaultConfig)
        let task = session.dataTask(with: urlRequest) { (data, response, error) in
            do {
                if let data = data {
                    let articles = try PropertyListDecoder().decode([Articles].self, from: data)
                    self.callBackOnMainThread(completion: completion, response: .success(response: PlistResponseData(results: articles)))
                }
            } catch {
                print(error)
                completion(.failure(error: error))
            }
        }
        task.resume()
    }

    private func callBackOnMainThread(completion: @escaping PListCompletion, response: PlistResponse) {
        DispatchQueue.main.async {
            completion(response)
        }
    }

final class ArticleListProvider {

     var articles: [Articles]

    convenience init() {
        self.init(articles: [])

        self.provideArticles { (article) in
            self.articles.append(contentsOf: article)
        }
    }

    init(articles: [Articles]) {
        self.articles = articles
    }

    func articleCount() -> Int {
//used for tableVC cells but returning 0
        return self.articles.count
    }

    func articleAtIndex(_ index: Int) -> Articles? {
        return articles[index]
    }

    func provideArticles(completion: @escaping ([Articles]) -> Void) {
        ArticleDetailsNetworkManager.sharedInstance.getArticles { [weak self] (response) in
            guard let weakSelf = self else { return}
            switch response {
            case .success(let plistData):
                weakSelf.articles = plistData.results
            case .failure(let error):
                print(error.localizedDescription)
            }
            completion(weakSelf.articles)
        }
    }
}

表VC

final class ArticleListController: UITableViewController {
    fileprivate let CellIdentifier = "Cell"

    fileprivate let articleListProvider: ArticleListProvider

    override init(style: UITableViewStyle) {
        self.articleListProvider = ArticleListProvider()
        super.init(style:style)
    }

    required init?(coder: NSCoder) {
        self.articleListProvider = ArticleListProvider()
        super.init(coder: coder)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        setupTableViewCell()
        tableView.reloadData()
    }
}

extension ArticleListController {

    func setupTableViewCell() {
        tableView.register(ArticleTableViewCell.self, forCellReuseIdentifier: CellIdentifier)
    }

    override func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

//this is returning 0 when it should be returning the amount of articles from the articleProvider, where the networking call is being made 

        return articleListProvider.articleCount()
    }

我不知道这是否重要，但这适用于 Xcode 9.4，（尽管没有回调），升级到 10.1 后出现此问题

Answer 1

这是一种期望的行为，api 调用是异步的，它不会立即返回任何内容。因此，在该 Web 服务返回结果之前，数组计数将为零。

改变你的初始化方法，如：

convenience init(callback: @escaping () -> Void) {
    self.init(articles: [])

    self.provideArticles { (article) in
        self.articles.append(contentsOf: article)
        callback()
    }
}

并通过以下方式从您的视图控制器中使用它：

self.articleListProvider = ArticleListProvider{ [weak self]
    guard let weakSelf = self else { return}
    weakSelf.yourTableView.reloadData()
}