I am trying to make a very simple app in MVVM and I must be missing something here but I can't figure it out. I have all the error handling in my NewsService class and I print success if all goes right and it receives the data. I get that success every time, the issue is the "print(articles)" are not printing anything at all.

class NewsTableViewModel {
    
    var articles = [Article]() {
        didSet {
            print(articles)
        }
    }
    
    func fetchNews() {

        NewsService.shared.fetchNews { [weak self] articles in
            guard let self = self else { return }
            self.articles = articles
            print(articles)
        }
    }
}

class NewsTableVC: UITableViewController, NewsTableViewModelDelegate {
    
    private let reuseIdentifier = "ArticleCell"
    private let newsTableVM = NewsTableViewModel()
    //    var article = [Article]() {
    //        didSet {
    //            DispatchQueue.main.async {
    //                self.tableView.reloadData()
    //            }
    //        }
    //    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        newsTableVM.delegate = self
        newsTableVM.fetchNews()
        updateUI()
    }
    
    func updateUI() {
        tableView.register(ArticleCell.self, forCellReuseIdentifier: reuseIdentifier)
        DispatchQueue.main.async {
            self.tableView.reloadData()
        }
    }
    
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        //        return article.count
        return self.newsTableVM.articles.count
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifier, for: indexPath) as! ArticleCell
        //        cell.articleTitleLabel.text = article[indexPath.row].title
        //        cell.articleDescriptionLabel.text = article[indexPath.row].description
        cell.articleTitleLabel.text = newsTableVM.articles[indexPath.row].title
        cell.articleDescriptionLabel.text = newsTableVM.articles[indexPath.row].description
        return cell
    }

}

struct Response: Codable {
    
    let articles: [Article]
}

struct Article: Codable {
    
    let title: String
    let description: String
}

class NewsService {
    
    static let shared = NewsService()
    
    func fetchNews(completion: @escaping ([Article]) -> (Void)) {
        
        if let urlString = URL(string: "") {
            
            let task = URLSession.shared.dataTask(with: urlString) { data, response, error in
                if let _ = error {
                    print("error")
                    return
                }
                
                guard let response = response as? HTTPURLResponse, response.statusCode == 200 else { return }
                
                guard let data = data else {
                    return
                }
                
                let decoder = JSONDecoder()
                do {
                    print("success")
                    let articles = try decoder.decode(Response.self, from: data).articles
                    completion(articles)
                } catch {
                    return
                }
            }
            task.resume()
        }
    }
}

In my view controller viewDidLoad, I call NewsTableViewModel().fetchNews(). And here is the entire NewsTableViewModel class. Ignore the double use of print(articles), I'm just trying to figure out where it's going wrong.

CodePudding user response：

you did not cover all the cases, put debug print at:

guard let self = self else { 
    print("self is nill")
    return completion([])
}

and:

            guard let response = response as? HTTPURLResponse, response.statusCode == 200 else { 
                print("error: \(response)")
                return completion([])
            }
            
            guard let data = data else {
                print("error: data is nill")
                return completion([])
            }

and:

            do {
                print("success")
                let articles = try decoder.decode(Response.self, from: data).articles
                completion(articles)
            } catch (let error){
                print("catch an error: \(error)
                completion([])
            }

also put the completion([]) in the error cases instead of return only.