ios - Swift - 在 vi​​ewDidLoad() 中完成 http 请求之前查看负载

Question

我正在尝试从数据库加载一个值，并将它们放入我的一个 Swift 文件中 viewDidLoad 函数的 UITableView 中。调试时，在 View 呈现时，值列表为空，但在 View 加载后，列表会被 View 加载填充。我对 Swift 中的线程没有太多经验，所以我不确定为什么会这样，有什么想法吗？我尝试运行 DispatchQueue.main.async，但没有成功 我的代码如下:

override func viewDidLoad() {

    super.viewDidLoad()

    // Load any saved meals, otherwise load sample data.
    loadDbMeals()

}

private func loadDbMeals()  {

    var dbMeals = [Meal]()

    let requestURL = NSURL(string: self.URL_GET)

    let request = NSMutableURLRequest(url: requestURL! as URL)

    request.httpMethod = "GET"

    //creating a task to send the post request
    let task = URLSession.shared.dataTask(with: request as URLRequest){
        data, response, error in

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

        //parsing the response
        do {
            //converting response to NSDictionary
            let myJSON = try JSONSerialization.jsonObject(with: data!, options: [.mutableContainers]) as? NSDictionary

            //parsing the json
            if let parseJSON = myJSON {

                if let nestedDictionary = parseJSON["message"] as? NSArray {
                    for meal in nestedDictionary {
                        if let nestedMeal = meal as? NSDictionary {
                            let mealName = nestedMeal["name"]
                            let rating = nestedMeal["rating"]
                            dbMeals.append(Meal(name: mealName as! String,  photo: UIImage(named: "defaultPhoto"), rating: rating as! Int, ingredientList: [])!)

                        }
                    }

                }

            }
        } catch {
            print(error)
        }

    }

    meals += dbMeals
    //executing the task
    task.resume()

}

所以，当前的断点顺序，是在viewDidLoad()函数中调用loadDbMeals()，然后尝试将dbMeals变量添加到全局meals变量中，然后执行http请求，空后列表已经添加。感谢您的帮助!

Answer 1

加载数据后重新加载表格

if let parseJSON = myJSON {

                if let nestedDictionary = parseJSON["message"] as? NSArray {
                    for meal in nestedDictionary {
                        if let nestedMeal = meal as? NSDictionary {
                            let mealName = nestedMeal["name"]
                            let rating = nestedMeal["rating"]
                            dbMeals.append(Meal(name: mealName as! String,  photo: UIImage(named: "defaultPhoto"), rating: rating as! Int, ingredientList: [])!)

                        }
                    }
                  DispatchQueue.main.async{
                      self.tableView.reloadData() 
                  }
                }

            }