Ios 如何等待另一个值被分配到run.onAppear？

我正在学习从头开始为iOS开发应用程序。我选择了SwiftUI来制作一个应用程序，它可以获取用户的位置，通过地理编码获取他所在的城市，并通过获取的信息，从API中显示属于该城市的项目列表

因此，我一方面学会了如何获取位置，另一方面学会了如何显示列表。我现在的问题是，当您运行.onAppear（perform:loadData）显示我的列表时，“city”结果仍然是空的。显然，城市的值是在我尝试显示城市列表后获得的

我必须得到位置的算法和我必须单独显示列表的算法都有效

所以我的代码是：

import SwiftUI

struct Response: Codable {
    var cinemas: [Cinema]
}

struct Cinema: Codable {
    var _id: String
    var cinemaName: String
    var cinemaCategory: String
}

struct HomeScreenView: View {
    
    @State var results = [Cinema]()
    
    @ObservedObject var lm = LocationManager()

    var latitude: String  {
        return("\(lm.location?.latitude ?? 0)") }
    var longitude: String { return("\(lm.location?.longitude ?? 0)") }
    var placemark: String { return("\(lm.placemark?.description ?? "XXX")") }
    var status: String    { return("\(lm.status)") }
    
    var city: String {
        return("\(lm.placemark?.locality ?? "empty")")
    }
    
    var body: some View {
        VStack {
            List(results, id: \._id) { item in
                VStack(alignment: .leading) {
                    Text(item.cinemaName)
                        .font(.headline)
                    Text(item.cinemaCategory)
                }
            }.onAppear(perform: loadData)
        }
        
    }
    
    func loadData() {
        guard let url = URL(string: "https://mycinemasapi.com/cinemasbycity/\(self.city)") else {
            print("Invalid URL")
            return
        }
        
        let request = URLRequest(url: url)
        
        URLSession.shared.dataTask(with: request) { data, response, error in
            
            if let data = data {
                if let decodedResponse = try? JSONDecoder().decode(Response.self, from: data) {
                    // we have good data – go back to the main thread
                    DispatchQueue.main.async {
                        // update our UI
                        self.results = decodedResponse.cinemas
                    }
                    
                    // everything is good, so we can exit
                    return
                }
            }
            
            // if we're still here it means there was a problem
            print("Fetch failed: \(error?.localizedDescription ?? "Unknown error")")
            
        }.resume()
    }
}

更新： LocationManager类

import Foundation
import CoreLocation
import Combine

class LocationManager: NSObject, ObservableObject {
  private let locationManager = CLLocationManager()
  private let geocoder = CLGeocoder()
  let objectWillChange = PassthroughSubject<Void, Never>()

  @Published var status: CLAuthorizationStatus? {
    willSet { objectWillChange.send() }
  }

  @Published var location: CLLocation? {
    willSet { objectWillChange.send() }
  }

  override init() {
    super.init()

    self.locationManager.delegate = self
    self.locationManager.desiredAccuracy = kCLLocationAccuracyBest
    self.locationManager.requestWhenInUseAuthorization()
    self.locationManager.startUpdatingLocation()
  }

    
  @Published var placemark: CLPlacemark? {
    willSet { objectWillChange.send() }
  }

  private func geocode() {
    guard let location = self.location else { return }
    geocoder.reverseGeocodeLocation(location, completionHandler: { (places, error) in
      if error == nil {
        self.placemark = places?[0]
      } else {
        self.placemark = nil
      }
    })
  }
}

extension LocationManager: CLLocationManagerDelegate {
    func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {
        self.status = status
    }

    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard let location = locations.last else { return }
        self.location = location
        self.geocode()
    }
}

<代码>导入基础 导入核心定位 进口联合收割机 类位置管理器：NSObject，observeObject{ 私有let locationManager=CLLocationManager（） 私有let geocoder=CLGeocoder（） let objectWillChange=PassthroughSubject（） @已发布变量状态：CLAuthorizationStatus{ willSet{objectWillChange.send（）} } @发布的变量位置：CLLocation{ willSet{objectWillChange.send（）} } 重写init（）{ super.init（） self.locationManager.delegate=self self.locationManager.desiredAccuracy=KCallocationAccuracyBest self.locationManager.requestWhenUseAuthorization（） self.locationManager.startUpdatingLocation（） } @已发布变量placemark:CLPlacemark{ willSet{objectWillChange.send（）} } 专用func地理代码（）{ guard let location=self.location else{return} geocoder.reverseGeocodeLocation（位置，completionHandler:{（位置，错误）在 如果错误==nil{ self.placemark=位置？[0] }否则{ self.placemark=nil } }) } } 扩展位置管理器：CLLocationManagerDelegate{ func locationManager（\ manager:CLLocationManager，didChangeAuthorization状态：CLAuthorizationStatus）{ self.status=状态 } func locationManager（manager:CLLocationManager，didUpdateLocations位置：[CLLocation]）{ guard let location=locations.last else{return} self.location=位置 self.geocode（） } }

---

正如您的代码一样，只需在收到的placemark上加载数据，如

        List(results, id: \._id) { item in
            VStack(alignment: .leading) {
                Text(item.cinemaName)
                    .font(.headline)
                Text(item.cinemaCategory)
            }
        }.onReceive(lm.$placemark) {
            if $0 != nil {
               self.loadData()
            }
        }

---

没有完整的代码很难回答这个问题。问题是，当您初始化城市时，LocationManager尚未设置。我会尝试在LocationManager中将city设置为一个变量，并在初始化期间进行设置，无论何时需要访问它，都可以调用lm。city@purebreadd我认为没有必要，但请检查我添加LocationManager类的更新。在这个类的init（）中，您要在其中添加lm.city吗？你能告诉我你将如何做，以及你以后在HomeScreenView中如何使用它吗？