ios - 如何重新加载 View Controller 以便 JSON 更新？

Question

我正在将一些 JSON 数据加载到 UITableView 中。每个单元格都有一个删除按钮，按下此按钮时，对象将成功从服务器中删除。但是，该页面不会更新以反射(reflect)此更改。我希望重新加载 TableView ，但不删除已删除的对象。我尝试过调用 viewDidLoad() 和 viewDidAppear() 以及我在网上找到的其他几个技巧。目前，我正在使用一种解决方法，将用户发送回主页。从那里，当您单击具有 TableView 的页面时，它已更新以反射(reflect)更改。然而，如果不离开 View Controller 并返回它，我似乎无法实现这一点。我知道 API 调用工作正常，只是页面没有“刷新”。我应该怎样努力才能使这项工作发挥作用？非常感谢!我整个类(class)的代码如下(我添加了一些注释来指出我遇到问题的地方)

import UIKit

class Garage: UIViewController, UITableViewDelegate, UITableViewDataSource {
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return self.vehicles.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell1", for: indexPath) as UITableViewCell
        cell.textLabel?.text = vehicles[indexPath.row].year + "   " + vehicles[indexPath.row].make + "   " + vehicles[indexPath.row].model
        let button = UIButton(type: .custom)
        button.backgroundColor = UIColor.green
        button.sizeToFit()
        cell.accessoryType = .detailButton
        return cell
    }

    func tableView(_ tableView: UITableView, accessoryButtonTappedForRowWith indexPath: IndexPath) {
        print("tapped")
        let alert = UIAlertController(title: "Would you like to delete this vehicle?", message: "This action cannot be undone.", preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: "No", style: .cancel, handler: nil))

        self.present(alert, animated: true)
        alert.addAction(UIAlertAction(title: "Yes", style: .default, handler: { action in
            print("DELETED")
            //
            //THIS IS WHERE THE DELETE ACTION IS CALLED
            //
            var id = self.vehicles[indexPath.row].id
            print("got here 1")

            let api = "https://api.myapi.com/"
            let parameters: [String: String] = ["id": id]
            guard let url = URL(string: api + id) else { return }
            var request = URLRequest(url: url)

            let headers: [String: String] = [
                "Content-Type": "application/json"
            ]
            request.allHTTPHeaderFields = headers
            request.httpMethod = "DELETE"
            let requestBody = try? JSONSerialization.data(withJSONObject: parameters, options: [])
            if let requestBody = requestBody {
                request.httpBody = requestBody
            }
            //
            //THIS IS WHERE I TRY TO RELOAD THE PAGE
            //
            print("reloading...")
            self.viewDidLoad()
            self.viewWillAppear(true)
            URLSession.shared.dataTask(with: request) { (data, response, error) in
                // print("Data, response, error", data, response, error)
                if let data = data {
                    let json = try? JSONSerialization.jsonObject(with: data, options: []) as? [String: Any] ?? [:]
                    print("json", json)
                }
                DispatchQueue.main.async {
                    self.tableVehicles.reloadData()
                    self.view.setNeedsLayout()
                    self.performSegue(withIdentifier: "GarageToHome", sender: self)
                }

                }.resume()
            //
            //THIS IS MY CURRENT WORK-AROUND
            //
            self.performSegue(withIdentifier: "GarageToHome", sender: self)
        }))
    }

    @IBOutlet weak var label1: UILabel!

    struct Vehicle {
        var make: String
        var model: String
        var year: String
        var Trim: String
        var id: String
        init(_ dictionary: [String: Any]) {
            self.make = dictionary["make"] as? String ?? ""
            self.model = dictionary["model"] as? String ?? ""
            self.year = dictionary["year"] as? String ?? ""
            self.Trim = dictionary["trim"] as? String ?? ""
            self.id = dictionary["id"] as? String ?? ""
        }
    }

    var vehicles = [Vehicle]()
    @IBOutlet weak var tableVehicles: UITableView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // print("login name:", username)
        self.tableVehicles.delegate = self
        self.tableVehicles.dataSource = self
        self.tableVehicles.reloadData()

    }

    override func viewWillAppear(_ animated: Bool) {
        //vehicles = [Vehicle]()
        let defaults = UserDefaults.standard
        defaults.synchronize()
        let token = UserDefaults.standard.string(forKey: "token")
        let isSignedIn = UserDefaults.standard.bool(forKey: "isUserLoggedIn")
        var username = UserDefaults.standard.string(forKey: "loginName")
        defaults.synchronize()
        DispatchQueue.main.async {
            self.label1.text = "Welcome, " + username! + "!"
            defaults.synchronize()
        }

        guard let url = URL(string: "https://api.myapi.com") else {return}
        let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
            guard let dataResponse = data,
                error == nil else {
                    print(error?.localizedDescription ?? "Response Error")
                    return }
            do{
                let jsonResponse = try JSONSerialization.jsonObject(with:
                    dataResponse, options: [])
                //print(jsonResponse) //Response result
                guard let jsonArray = jsonResponse as? [[String: Any]] else {
                    return
                }
                for dic in jsonArray{
                    self.vehicles.append(Vehicle(dic))
                }
                print(self.vehicles)
                DispatchQueue.main.async {
                    self.tableVehicles.delegate = self
                    self.tableVehicles.dataSource = self
                    self.tableVehicles.reloadData()
                }
            } catch let parsingError {
                print("Error", parsingError)
            }
        }
        task.resume()
    }
}

Answer 1

首先，永远不要自己调用包含 will、did 和 should 的委托(delegate)方法。不要那样做。这些方法仅由框架调用。

有一个非常简单的解决方案。您知道已删除行的索引路径，因此如果数据任务成功，则从数据源数组中删除该项目并删除 TableView 中的行。无需重新加载整个 TableView 并根据下载的数据更新数据源数组。

无论如何，您需要一个明确的指示服务器操作是否成功的指标，我不知道 dataTask 中的 if let data = data 是否足够。

//THIS IS WHERE I TRY TO RELOAD THE PAGE
//
print("reloading...")
URLSession.shared.dataTask(with: request) { (data, response, error) in
   // print("Data, response, error", data, response, error)
   if let data = data {
      let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any] ?? [:]
      print("json", json)
      DispatchQueue.main.async {
         self.vehicles.remove(at: indexPath.row)
         tableView.deleteRows(at: [indexPath], with: .fade)
         self.performSegue(withIdentifier: "GarageToHome", sender: self)
      }
   }
}.resume()