为什么不显示新视图控制器的表视图？迅速

Question

这是以下问题的后续措辞：如何调用可以呼叫API调用的类的实例，以及在该类中的函数，并将其分配给变量？迅速。

我正在尝试将新的视图控制器推向堆栈，并从初始视图控制器中呈现此视图控制器，但是当我运行程序时，应该在新视图控制器中显示的表视图不加载在模拟器上。在运行程序之前，之中或之后，我根本没有任何错误通知。另外，似乎并没有在此新视图控制器中执行代码，因为新View Controller类的顶部/非常开头的打印语句（和View Controller .swift File）未打印。

当应该显示新的视图控制器的新表视图时所显示的是空白屏幕，但是导航栏仍在顶部，而导航栏的左上方则显示了后面的按钮（就像通常是一样当正确显示表视图之前，在更改Yelpapi类作为API请求并使用异步/等待时）。发生这种情况时，我也不会在终端中收到任何错误消息。

我认为与问题相关的是新的Yelpapi类，该类用于在此处和使用异步/等待API端点请求。直到我使用此新类和异步/等待代码重构后，这个问题才发生。

我认为可能会更具体地引起问题，是在“ func viewDidload（）async {” newviewController.swift之前取出“覆盖”。我之所以这样做，是因为我将其放在那里时会遇到错误，并发现该解决方案建议将其取出，但是，这样做的问题如接受答案所述（问题是没有问题编译时间检查确保您的签名正确）： SWIFT协议：方法不会从其超类中覆盖任何方法。

我已经在网上看到了这个问题（表视图未显示），包括此处，并且找不到工作解决方案。一篇类似的文章是：视图控制器不正确显示我的代码已经设置了类似地，以与公认答案相同的形式。我也让程序运行20分钟，然后再辞职，以防该请求仅出于任何原因而花费很长时间，但是，仍未介绍所需的表观视图。

代码：

drimationViewController.swift ：

//*Code for creating a table view that shows options to the user, for the user to select.*

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        
        //*Code for assigning values to variables related to what row in the table view the user selected.*
        
        
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let newVC = storyboard.instantiateViewController(identifier: "NewViewController") as! NewViewController
        newVC.modalPresentationStyle = .fullScreen
        newVC.modalTransitionStyle = .crossDissolve
        
        //Print Check.
        //Prints.
        print("Print Check: Right before code for presenting the new view controller.")

        navigationController?.pushViewController(newVC, animated: true)
        
    }

newViewController.swift

import UIKit
import CoreLocation

class NewViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
    
    //Print Check.
    //Doesn't print.
    func printCheckBeforeIBOutletTableViewCode() {
        print("Print Check: Right before tableView IBOutlet code at top of NewViewController.swift file.")
    }
    
    @IBOutlet var tableView: UITableView!
    
    var venues: [Venue] = []
    
    //Print Check.
    //Doesn't print.
    func printCheckAfterIBOutletTableViewCode() {
        print("Print Check: Right after tableView IBOutlet code at top of NewViewController.swift file.")
    }
    
    func viewDidLoad() async {
        super.viewDidLoad()
        
        //Function calls for print checks.
        //Doesn't print.
        self.printCheckBeforeIBOutletTableViewCode()
        self.printCheckAfterIBOutletTableViewCode()
        
        tableView.register(UINib(nibName: "CustomTableViewCell", bundle: nil), forCellReuseIdentifier: "CustomTableViewCell")
        tableView.delegate = self
        tableView.dataSource = self
        
        //Print Check.
        //Doesn't print.
        print("Print Check: Right before creating an instance of YelpApi class, then creating a task to make the API request.")
        
        let yelpApi = YelpApi(apiKey: "Api key")
        
        Task {
            do {
                self.venues = try await yelpApi.searchBusiness(latitude: selectedLatitude, longitude: selectedLongitude, category: "category query goes here", sortBy: "sort by query goes here")
                self.tableView.reloadData()
            } catch {
                    //Handle error here.
                    print("Error")
            }
        }
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
           return venues.count
       }
       
       func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
           let cell = tableView.dequeueReusableCell(withIdentifier: "CustomTableViewCell", for: indexPath) as! CustomTableViewCell
           
           //Details for custom table view cell go here.
       }
           
       //Rest of table view protocol functions.
    
}

venue.swift ：

import Foundation

// MARK: - BusinessSearchResult
struct BusinessSearchResult: Codable {
    let total: Int
    let businesses: [Venue]
    let region: Region
}

// MARK: - Business
struct Venue: Codable {
    let rating: Double
    let price, phone, alias: String?
    let id: String
    let isClosed: Bool?
    let categories: [Category]
    let reviewCount: Int?
    let name: String
    let url: String?
    let coordinates: Center
    let imageURL: String?
    let location: Location
    let distance: Double
    let transactions: [String]

    enum CodingKeys: String, CodingKey {
        case rating, price, phone, id, alias
        case isClosed
        case categories
        case reviewCount
        case name, url, coordinates
        case imageURL
        case location, distance, transactions
    }
}

// MARK: - Category
struct Category: Codable {
    let alias, title: String
}

// MARK: - Center
struct Center: Codable {
    let latitude, longitude: Double
}

// MARK: - Location
struct Location: Codable {
    let city, country, address2, address3: String?
    let state, address1, zipCode: String?

    enum CodingKeys: String, CodingKey {
        case city, country, address2, address3, state, address1
        case zipCode
    }
}

// MARK: - Region
struct Region: Codable {
    let center: Center
}

fetchdata.swift ：

import Foundation
import CoreLocation

class YelpApi {
    
    private var apiKey: String
    
    init(apiKey: String) {
        self.apiKey = apiKey
    }
    
    func searchBusiness(latitude: Double,
                        longitude: Double,
                        category: String,
                        sortBy: String) async throws -> [Venue] {
        
        var queryItems = [URLQueryItem]()
        queryItems.append(URLQueryItem(name:"latitude",value:"\(latitude)"))
        queryItems.append(URLQueryItem(name:"longitude",value:"\(longitude)"))
        queryItems.append(URLQueryItem(name:"categories", value:category))
        queryItems.append(URLQueryItem(name:"sort_by",value:sortBy))
       
        var results = [Venue]()
        
        var expectedCount = 0
        let countLimit = 50
        var offset = 0
        
        queryItems.append(URLQueryItem(name:"limit", value:"\(countLimit)"))
        
        repeat {
            
            var offsetQueryItems = queryItems
            
            offsetQueryItems.append(URLQueryItem(name:"offset",value: "\(offset)"))
            
            var urlComponents = URLComponents(string: "https://api.yelp.com/v3/businesses/search")
            urlComponents?.queryItems = offsetQueryItems
            
            guard let url = urlComponents?.url else {
                throw URLError(.badURL)
            }
            
            var request = URLRequest(url: url)
            request.setValue("Bearer \(self.apiKey)", forHTTPHeaderField: "Authorization")
            
            let (data, _) = try await URLSession.shared.data(for: request)
            let businessResults = try JSONDecoder().decode(BusinessSearchResult.self, from:data)

            expectedCount = min(businessResults.total,1000)
            
            results.append(contentsOf: businessResults.businesses)
            offset += businessResults.businesses.count
        } while (results.count < expectedCount)
        
        return results
    }
}

谢谢！

---

更新：

从Andreas和Paulw11的建议进行更改之后，该程序运行时仍未加载表视图，我在终端中从 catch> catch block中获得了最后的打印语句是“错误”在任务创建Yelpapi类的实例之后，在 newViewController.swift 中创建了初始API请求。从那以后，我将文件中的“错误”语句更改为“在制作初始API端点请求时发生错误”。为了清楚。

以下是 newViewController.swift 的更新版本，其中包括Andreas和paulw11建议的更改，以及 fetchdata.swift ，并带有新的打印语句，以帮助识别新问题。在这些更新的版本下方是对Andreas和Paulw11的建议更改后的终端的返回语句，该更改还包含FetchData.Swift更新版本中的新打印语句（以帮助识别新问题）。

newViewController.swift 的更新版本替代插入和 async 删除：

import UIKit
import CoreLocation

class NewViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
    
    //Print Check.
    //Prints.
    func printCheckBeforeIBOutletTableViewCode() {
        print("Print Check: Right before tableView IBOutlet code at top of NewViewController.swift file.")
    }
    
    @IBOutlet var tableView: UITableView!
    
    var venues: [Venue] = []
    
    //Print Check.
    //Prints.
    func printCheckAfterIBOutletTableViewCode() {
        print("Print Check: Right after tableView IBOutlet code at top of NewViewController.swift file.")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        //Function calls for print checks.
        //Prints.
        self.printCheckBeforeIBOutletTableViewCode()
        self.printCheckAfterIBOutletTableViewCode()
        
        tableView.register(UINib(nibName: "CustomTableViewCell", bundle: nil), forCellReuseIdentifier: "CustomTableViewCell")
        tableView.delegate = self
        tableView.dataSource = self
        
        //Print Check.
        //Prints.
        print("Print Check: Right before creating an instance of YelpApi class, then creating a task to make the API request.")
        
        let yelpApi = YelpApi(apiKey: "Api key")
        
        Task {
            do {
                self.venues = try await yelpApi.searchBusiness(latitude: selectedLatitude, longitude: selectedLongitude, category: "category query goes here", sortBy: "sort by query goes here")
                self.tableView.reloadData()
            } catch {
                    //Handle error here.
                    //Prints.
                    print("Error")
            }
        }
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
           return venues.count
       }
       
       func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
           let cell = tableView.dequeueReusableCell(withIdentifier: "CustomTableViewCell", for: indexPath) as! CustomTableViewCell
           
           //Details for custom table view cell go here.
       }
           
       //Rest of table view protocol functions.
    
}

fetchdata.swift.swift 更新版本新的打印语句以帮助识别新问题：

import Foundation
import CoreLocation

class YelpApi {
    
    private var apiKey: String
    
    init(apiKey: String) {
        self.apiKey = apiKey
    }
    
    func searchBusiness(latitude: Double,
                        longitude: Double,
                        category: String,
                        sortBy: String) async throws -> [Venue] {
        
        var queryItems = [URLQueryItem]()
        queryItems.append(URLQueryItem(name:"latitude",value:"\(latitude)"))
        queryItems.append(URLQueryItem(name:"longitude",value:"\(longitude)"))
        queryItems.append(URLQueryItem(name:"categories", value:category))
        queryItems.append(URLQueryItem(name:"sort_by",value:sortBy))
       
        var results = [Venue]()
        
        var expectedCount = 0
        let countLimit = 50
        var offset = 0
        
        queryItems.append(URLQueryItem(name:"limit", value:"\(countLimit)"))
        
        //Print Check.
        //Prints.
        print("Print Check: Line before repeat-while loop.")
        
        repeat {
            
            //Print Check.
            //Prints.
            print("Print Check: Within repeat-while loop and before first line of code within it.")
            
            var offsetQueryItems = queryItems
            
            offsetQueryItems.append(URLQueryItem(name:"offset",value: "\(offset)"))
            
            var urlComponents = URLComponents(string: "https://api.yelp.com/v3/businesses/search")
            urlComponents?.queryItems = offsetQueryItems
            
            guard let url = urlComponents?.url else {
                throw URLError(.badURL)
            }
            
            var request = URLRequest(url: url)
            request.setValue("Bearer \(self.apiKey)", forHTTPHeaderField: "Authorization")
            
            //Print Check.
            //Prints.
            print("Print Check: Within repeat-while loop and before 'let (data, _) = try await' line of code.")
            let (data, _) = try await URLSession.shared.data(for: request)
            
            //Print Check.
            //Prints.
            print("Print Check: Within repeat-while loop and before 'let businessResults = try JSONDecoder()' line of code.")
            let businessResults = try JSONDecoder().decode(BusinessSearchResult.self, from:data)
            
            //Print Check.
            //Doesn't print.
            print("Print Check: Within repeat-while loop and right after 'let businessResults = try JSONDecoder()' line of code.")

            expectedCount = min(businessResults.total,1000)
            
            results.append(contentsOf: businessResults.businesses)
            offset += businessResults.businesses.count
        } while (results.count < expectedCount)
        
        //Print Check.
        //Doesn't print.
        print("Print Check: After repeat-while loop and before 'return results' code.")
        
        return results
    }
}

在制作Andreas和Paulw11的建议更改和运行程序 中返回的终端返回的打印语句：

Print Check: Right before code for presenting the new view controller.
Print Check: Right before tableView IBOutlet code at top of NewViewController.swift file.
Print Check: Right after tableView IBOutlet code at top of NewViewController.swift file.
Print Check: Right before creating an instance of YelpApi class, then creating a task to make the API request.
Print Check: Line before repeat-while loop.
Print Check: Within repeat-while loop and before first line of code within it.
Print Check: Within repeat-while loop and before 'let (data, _) = try await' line of code.
Date and Time, Project Name, and some other info [boringssl] boringssl_metrics_log_metric_block_invoke(153) Failed to log metrics
Print Check: Within repeat-while loop and before 'let businessResults = try JSONDecoder()' line of code.
Error occurred when making initial API endpoint request.

必须退出程序，因为它“停滞不前”/在进行最后一次之后什么也没做终端上的打印语句。

另外，“日期和时间，项目名称以及其他一些信息[boringssl] boringssl_metrics_metrics_log_metric_block_invoke（153）未能登录指标”，每当我提出API请求时，就会出现打印语句，并且在研究时，不会对任何问题造成任何问题。项目。

在“发出初始API端点请求时发生错误”之前打印的最后一个打印语句。是“打印检查：在重复循环中，然后在'Let businessResults = try jsondecoder（）'代码行之前。”表明代码的行中出现了问题，让businessResults = try jsondecoder（）。decode（butinessSearchResult.self，from：data），这使我认为问题可能正在发生并成为与类别和 sort_by 在 searchbusinesses yelpapi fetchdata.swift 中的类定义。我正在努力解决此问题，如果我弄清楚，将更新。

感谢您的帮助！

Answer 1

我认为您已经确定了其中一个问题。您的代码在 func viewDidload（）async 永远不会执行，因为没有人调用它。通过添加 async 您不再覆盖原始 uiviewController 方法。 （请参阅）
您可以删除 async 并再次覆盖它吗？我认为这至少应该执行代码，您应该看到打印语句。