如何等待所有数据完全下载并显示在TableView上？

Question

I have class named ShowCarClass

It will use TableView to show Car's name and image

class ShowCarClass:UIViewController {

@IBOutlet weak var tableView: UITableView!
var car = [Car]()

 override func viewDidLoad() {
        super.viewDidLoad()
    }

    func myAPI() {
         startAnimating()
         let json = CarType.Request
         api.getAPIResponse(apiURL:.Car ,jsonType: json) {(isSuccess, result) in

         switch isSuccess {

         case true: 
         let successResult = result as! CarType.Response
         //car array result like this
                 [Car(carName:"BMW",carImg:"https://00.00.00/static/image/BMW.png"),Car(carName:"Audi",carImg:"https://00.00.00/static/image/Audi.png")]
                 self.tableView.delegate = self
                 self.tableView.dataSource = self
                 self.tableView.reloadData()

         case false:
         self.APIErrorStatus(result)
                }
          stopAnimating()
           }
        }

When I press Button it can call myApi() and update tableview content

This ViewController has 3 buttons, it will separately get different data

@IBAction func btnPress(_ sender: UIButton) {
         callAPI()
}

In function cellForRowAt I use carImg's URL to download Image

extension ShowCarClass:UITableViewDelegate, UITableViewDataSource{
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return car.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! CarCell
        cell.carNameLabel.text = car[indexPath.row].carName
        cell.carImageView.downloaded(from:car[indexPath.row].carImg, contentMode: .scaleToFill)
        return cell
    }
}

Here's extension UIImageView

extension UIImageView {
    func downloaded(from url: URL, contentMode mode: UIView.ContentMode = .scaleAspectFit) {
        contentMode = mode
        URLSession.shared.dataTask(with: url) { data, response, error in

        guard   let httpURLResponse = response as? HTTPURLResponse, httpURLResponse.statusCode == 200,
                let mimeType = response?.mimeType, mimeType.hasPrefix("image"),
                let data = data, error == nil,
                let image = UIImage(data: data) else {
                    return
            }

            DispatchQueue.main.async() {
                self.image = image
            }

            }
            .resume()
    }

    func downloaded(from link: String, contentMode mode: UIView.ContentMode = .scaleAspectFit) {
        guard let url = URL(string: link) else { return }
        downloaded(from: url, contentMode: mode)
    }
}

In ShowCarClass I show startAnimating when call myAPI()

but I need to use image URL to download image

This situation will make start and stop animate finish too quickly

TableView looks like I actually get that data I need

but Car's array content have URL I have to additionally process

I hope it can download all of the image, and implement stopAnimating

Step is like : user open app -> call myApi() -> startAnimating -> All of

the carName and CarImage completely -> stopAnimating -> load into TableView

-> user can see all the car informations (can't swipe tableview until data finished)

I'm really new, not good at questioning if need more info just ask for me, Thanks.

Answer 1

You can use DispatchGroup

let dispatchGroup = DispatchGroup()

let imageCount = 10

for _ in 1...imageCount{
   dispatchGroup.enter()
   ImageDownloader.download(image: "url") { result in
      dispatchGroup.leave()
   }
}

dispatchGroup.notify(queue: .main) 
    tableView.reloadData()
}