用户输入的值保存到 Core Data (?) 但未出现在表视图中

Question

我一直在努力让用户输入的值在我正在处理的项目的表格视图中正确显示。

我获取用户输入值的方法是让用户在文本字段中输入信息（公司名称、股票代码和徽标的 URL），然后在按下完成按钮时调用 handleSave()：

func handleSave() {

let newCompanyName = nameTextField.text
guard let newCompanyStockSymbol = stockTextField.text else {
    // handle the error how you see fit
    print("error getting text from field")
    return
}
let newCompanyLogo = logoTextField.text

var newCompanyStockPrice = ""

// Fetch stock price from symbol provided by user for new company
let url = URL(string: "https://query.yahooapis.com/v1/public/yql?q=select%20symbol%2C%20Ask%2C%20YearHigh%2C%20YearLow%20from%20yahoo.finance.quotes%20where%20symbol%20in%20(%22\(newCompanyStockSymbol)%22)&format=json&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys")!
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
    if error != nil {
        print(error!)
    } else if let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 {
        let json = JSON(data: data!)
        if let quotes = json["query"]["results"]["quote"].array {
            for quote in quotes {
                let ask = quote["Ask"].stringValue
                newCompanyStockPrice = ask
            }
        }
    }
    self.viewController?.save(name: newCompanyName!, logo: newCompanyLogo!, stockPrice: newCompanyStockPrice)
    //self.viewController?.tableView.reloadData()
}
task.resume()



let cc = UINavigationController()
let companyController = CompanyController()
cc.viewControllers = [companyController]
present(cc, animated: true, completion: nil)
}

然后调用此save 函数，将值保存到托管上下文中。

func save(name: String, logo: String, stockPrice: String) {

guard let appDelegate =
    UIApplication.shared.delegate as? AppDelegate else {
        return
}

let managedContext =
    appDelegate.persistentContainer.viewContext

let entity =
    NSEntityDescription.entity(forEntityName: "Company",
                               in: managedContext)!
let company = NSManagedObject(entity: entity,
                              insertInto: managedContext)


company.setValue(stockPrice, forKey: "stockPrice")
company.setValue(name, forKey: "name")
company.setValue(logo, forKey: "logo")


do {
    try managedContext.save()
    companies.append(company)
} catch let error as NSError {
    print("Could not save. \(error), \(error.userInfo)")
}

tableView.reloadData()
}

如果我在我的handleSave() 函数中调用self.viewController?.save(name: newCompanyName!, logo: newCompanyLogo!, stockPrice: newCompanyStockPrice) 时放置一个断点，我可以看到所有三件事（newCompanyName、newCompanyLogo 和newCompanyStockPrice）都有值。但是当我尝试在cellForRow 中设置新公司时，它并没有出现在我的表格视图中：

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return companies.count
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell = tableView.dequeueReusableCell(withIdentifier: cellId, for: indexPath) as! Cell
    let company = companies[indexPath.row]
    let stock = company.value(forKey: "stockPrice") as? String

    // Company name labels
    cell.textLabel?.text = company.value(forKey: "name") as? String


    // Stock price underneath
    if let stock = stock {
        cell.detailTextLabel?.text = "Current stock price: \(stock)"
    }

    // Logos
    DispatchQueue.main.async {
    if let url = NSURL(string: (company.value(forKey: "logo") as? String)!) {
        if let data = NSData(contentsOf: url as URL) {
            cell.logoView.image = UIImage(data: data as Data)
        } else {
            cell.logoView.image = UIImage(named: "noImage")
        }
    }
    }
    return cell
}

编辑：viewWillAppear

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

    //1
    guard let appDelegate =
        UIApplication.shared.delegate as? AppDelegate else {
            return
    }

    let managedContext =
        appDelegate.persistentContainer.viewContext

    //2
    let fetchRequest =
        NSFetchRequest<NSManagedObject>(entityName: "Company")

    //3
    do {
        companies = try managedContext.fetch(fetchRequest)
    } catch let error as NSError {
        print("Could not fetch. \(error), \(error.userInfo)")
    }

}

Answer 1

我建议将重新加载数据的调用明确地放在主队列中。在我看来，您正在从 dataTask 完成处理程序中调用 func save(name: String, logo: String, stockPrice: String)，然后在该线程上调用 reloadData。

因此，在save 函数中，将其包装成这样：

DispatchQueue.main.async { [weak self] in 
    self?.tableView.reloadData()
}