為什么新視圖控制器的表格視圖不顯示？迅速-有解無憂

這是以下問題的后續：如何呼叫進行 API 呼叫的類的實體，以及該類中發出請求的函式，并將其分配給變數？斯威夫特。

我正在嘗試將新的視圖控制器推送到堆疊上，并從初始視圖控制器中呈現此視圖控制器，但是當我運行程式時，應該在新視圖控制器中顯示的表視圖不會加載在模擬器上。在運行程式之前、期間或之后，我根本沒有來自 Xcode 的任何錯誤通知。此外，似乎沒有在這個新的視圖控制器中執行代碼，因為新視圖控制器類（和視圖控制器 .swift 檔案）的頂部/最開頭的列印陳述句沒有被列印。

當應該顯示來自新視圖控制器的新表視圖時顯示的是一個空白螢屏，但導航欄仍在頂部，導航欄左上方的后退按鈕（通常是在更改為對 API 請求使用 YelpApi 類并使用 async/await 之前正確顯示表視圖時）。發生這種情況時，我也沒有在終端中收到任何錯誤訊息。

我認為與該問題相關的是新的 YelpApi 類，該類用于在此處發出 API 端點請求，并使用 async/await。直到我使用這個新類和 async/await 重構了我的代碼之后，這個問題才出現。

我認為可能導致問題更具體的原因是，我在 NewViewController.swift 中的“func viewDidLoad() async {”之前取出了“覆寫”。我這樣做是因為我把它放在那里時遇到了一個錯誤，并找到了建議將其取出的解決方案，但是，如已接受答案的評論中所述，這樣做存在問題（問題是沒有編譯時檢查以確保您的簽名正確）：Swift 協議：方法不會覆寫其超類中的任何方法。

我已經在網上（包括此處）查看了這個問題（表格視圖未顯示），但找不到有效的解決方案。一篇類似的帖子是這樣的：View Controller 沒有正確顯示，但我的代碼已經以與接受的答案類似的形式設定。我還讓程式在退出程式之前運行了 20 分鐘，以防請求因某種原因而花費很長時間，但是仍然沒有顯示所需的表格視圖。

代碼：

InitialViewController.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 quary goes here", sortBy: "sort by quary 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
    }
}

謝謝！

更新：

在根據 Andreas 和 Paulw11 的建議進行更改后，運行程式時表格視圖仍然沒有加載，并且我在創建 YelpApi 類的實體之后的catch塊中的終端中的最后一個列印陳述句是“錯誤”Task在中發出初始 API 請求NewViewController.swift。我已經將檔案中的這個“錯誤”陳述句更改為“發出初始 API 端點請求時發生錯誤”。為了清楚起見。

NewViewController.swift以下是Andreas 和 Paulw11 建議的更改的更新版本，以及FetchData.swift用于幫助識別新問題的新列印宣告。在這些更新版本的下方是在做出 Andreas 和 Paulw11 的建議更改后來自終端的回傳陳述句，其中還包含 FetchData.swift 更新版本中的新列印陳述句（用于幫助識別新問題）。

插入和取出NewViewController.swift的更新版本：overrideasync

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 quary goes here", sortBy: "sort by quary 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.
    
}

更新版本FetchData.swift包括新的列印陳述句以幫助識別新問題：

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
    }
}

Returned Print Statements from Terminal Returned After Making Andreas and Paulw11's Suggested Changes and Running Program：

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.

不得不退出程式，因為它“停止”/在終端中做出上面的最后一個列印陳述句后什么也沒做。

此外，每當我提出 API 請求時，都會出現“日期和時間、專案名稱和其他一些資訊 [boringssl]boringssl_metrics_log_metric_block_invoke(153) 無法記錄指標”列印陳述句，并且在研究時不會對專案。

在“發出初始 API 端點請求時發生錯誤”之前列印的最后一條列印陳述句。正在“列印檢查：在重復回圈內和'讓 businessResults = 嘗試 JSONDecoder()' 代碼行之前。” 表明代碼行出現let businessResults = try JSONDecoder().decode(BusinessSearchResult.self, from:data)問題，這使我認為問題可能正在發生，并且與在類定義的函式中附加quarryItemsforcategory和時有關。我正在努力解決這個問題，如果我解決了這個問題，我會更新。sort_bysearchBusinessesYelpApiFetchData.swift

感謝所有的幫助！

uj5u.com熱心網友回復：

我認為您已經確定了其中一個問題。你的代碼func viewDidLoad() async永遠不會被執行，因為沒有人呼叫它。通過添加async，您不再覆寫原始UIViewController方法。（請參閱https://developer.apple.com/documentation/uikit/uiviewcontroller/1621495-viewdidload）您可以洗掉async并再次覆寫它嗎？我認為這至少應該執行代碼，你應該看到你的列印陳述句。

轉載請註明出處，本文鏈接：https://www.uj5u.com/gongcheng/486945.html

標籤：IOS 迅速异步等待视图控制器 yelp-融合-api

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