无法使用 mapKit 从 ViewController 将坐标发送到具有委托的另一个 viewController

Question

我是 Swift 和 iOS 开发的新手。我有一个问题，我通过标签栏导航控制器连接了三个 viewController。第一个 viewController 现在是空的并且没有被使用。在 secondViewController 中，我使用来自天气 API 的数据更新 UI。在thirdViewController 我有一张地图。当我访问地图时，我需要坐标来更新 secondViewController 中的 url。

我想要实现的是在 thirdViewController 中检索当前的纬度和经度（没问题），但我无法通过委托发送这些值以触发 secondViewController 中的功能，从而更新里面的变量。 secondViewController 中的委托函数只是没有被触发。我究竟做错了什么？或者甚至可以这样做吗？

两个viewController的代码如下：

secondViewController（这是我需要在thirdViewController 中的地图值的地方）

import UIKit

class SecondViewController: UIViewController, MapViewControllerDelegate {

    var forecastData: [ForecastData] = []
    var currentLat: String = "59.911166"
    var currentLon: String = "10.744810"
    
    @IBOutlet weak var tableView: UITableView!
    
    var weatherManager = WeatherManager()
    var mapViewController = ThirdViewController()
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        mapViewController.delegate = self
        weatherManager.delegate = self
        weatherManager.fetchWeather(latitude: currentLat, longitude: currentLon)
        tableView.backgroundView = UIImageView(image: UIImage(named: "background"))
        tableView.dataSource = self
        tableView.register(UINib(nibName: "WeatherCell", bundle: nil), forCellReuseIdentifier: "WeatherCell")
        
    }
    
    func viewDidAppear() {
        weatherManager.fetchWeather(latitude: currentLat, longitude: currentLon)
        
    }
    
    
    // THIS FUNCTION SHOULD BE TRIGGERED BUT DOESN'T
    
    func mapViewController(latitude: String, longitude: String) {
        currentLat = latitude
        currentLon = longitude
        print(currentLat)
        print(currentLon)
        print("DELEGATE METHOD TRIGGERED")
    }

}

//MARK: - WeatherManagerDelegate

extension SecondViewController: WeatherManagerDelegate {
    
    func didUpdateWeather(_ weatherManager: WeatherManager, weather: WeatherModel) {
        
        forecastData.append(ForecastData(timespan: "Nå", precipitation: "", tempOrWeather: "Temperatur", tempWeatherLabel: "\(weather.temperatureNow)" + " " + "\(weather.tempUnits)"))
        
        forecastData.append(ForecastData(timespan: "Neste Time", precipitation: "\(weather.precipitationNext1H)" + " " + "\(weather.precipUnits)", tempOrWeather: "vær", tempWeatherLabel: String(weather.conditionNext1H) ))
        
        forecastData.append(ForecastData(timespan: "Neste 6 timer", precipitation: "\(weather.precipitationNext6H)" + " " + "\(weather.precipUnits)", tempOrWeather: "vær", tempWeatherLabel: String(weather.conditionNext6H)))
        
        forecastData.append(ForecastData(timespan: "Neste 12 timer", precipitation: "", tempOrWeather: "vær",  tempWeatherLabel: String(weather.conditionNext12H)))
        
        DispatchQueue.main.async {
            self.tableView.reloadData()
        }
        
    }
    
    func didFailWithError(error: Error) {
        print(error)
    }
}

extension SecondViewController: UITableViewDataSource {
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return forecastData.count
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "WeatherCell", for: indexPath)
        as! WeatherCell
        cell.TimeframeLabel.text = forecastData[indexPath.row].TimeframeLabel
        cell.TempLabel.text = forecastData[indexPath.row].TempLabel
        cell.WeatherCodeLabel.text = forecastData[indexPath.row].WeatherCodeLabel
        cell.PrecipitationLabel.text = forecastData[indexPath.row].PrecipitationLabel
        return cell
    }
}

thirdViewController（这是我尝试通过委托传递坐标值的地方）

import UIKit
import MapKit
import CoreLocation

protocol MapViewControllerDelegate {
    func mapViewController(latitude: String, longitude: String)
}

class ThirdViewController: UIViewController, MKMapViewDelegate {
    
    var currentLat = ""
    var currentLon = ""
    @IBOutlet weak var mMapView: MKMapView!
    fileprivate let locationManager: CLLocationManager = CLLocationManager()
    var delegate: MapViewControllerDelegate?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        locationManager.requestWhenInUseAuthorization()
        locationManager.desiredAccuracy = kCLLocationAccuracyBest
        locationManager.distanceFilter = kCLDistanceFilterNone
        locationManager.startUpdatingLocation()
        
        mMapView.showsUserLocation = true
               
        currentLat = String((locationManager.location?.coordinate.latitude)!)
        currentLon = String((locationManager.location?.coordinate.longitude)!)
        
        print(currentLat)
        print(currentLon)
        
        //delegate?.mapViewController(latitude: "TESTlon", longitude: "TESTlati")
    }
    
    override func viewDidAppear(_ animated: Bool) {
        updateWeatherView()
    }
    
    // THIS SHOULD TRIGGER THE DELEGATE FUNCTION IN SECOND VIEW CONTROLLER AND PASS THE DATA ALONG
    func updateWeatherView() {
        delegate?.mapViewController(latitude: "TESTlon", longitude: "TESTlati")
    }
    
}

我尝试了不同的方法，但似乎没有任何效果，secondViewController 中的委托函数没有被触发。同样，我对此很陌生，所以也许这是一件简单的事情。提前感谢您的帮助！另外，如果有帮助，这里是我的故事板的屏幕截图：

Answer 1

正如@Duncan C 所说，做

var weatherManager = WeatherManager()
var mapViewController = ThirdViewController()

只需创建这些视图控制器的新实例——这些与您已有的完全无关。当然，如果您执行mapViewController.delegate = self，您正在设置mapViewController 的委托...但mapViewController 不是您想要的视图控制器。

要获得您想要的视图控制器，您可以访问标签栏控制器的视图控制器（当您在情节提要中创建它们时，它们会自动为您创建），然后选择正确的：

if 
    let viewControllers = self.tabBarController?.viewControllers, 
    viewControllers.count >= 3,
    let thirdViewController = viewControllers[2] as? ThirdViewController /// [2] because that's the third view controller in the array, which is the one you want
{
    thirdViewController.delegate = self
}

self.tabBarController 可能为零，因此您需要将其解包。然后，您应该确保有 3 个以上的视图控制器。最后，您需要将所需的视图控制器 (self.tabBarController?.viewControllers[2]) 转换为 ThirdViewController。然后，您可以将委托设置为该视图控制器。