SwiftUI

Question

这个问题困扰了我几个月，我相信这归结于我使用了错误的结构和程序。

我正在尝试对 Yelp 的 API 进行 API 调用，并为用户的 lat/long 传递变量。我可以根据我当前的 LocationManager 获取 lat/long，但是当 lat/long 似乎只在调用 API 之后可用时，所以 API 正在为 lat/long.

获取默认的 0.0 值

在这方面我是一个初学者，但有没有一种方法可以设置一个加载屏幕，在后台抓取 lat/long 并在我的 ExploreView 显示时，真实位置信息已经建立？

下面是我的 LocationManager 和 ExploreView

位置管理器

import Foundation
import CoreLocation

class LocationManager: NSObject, ObservableObject {

private let locationManager = CLLocationManager()
let geoCoder = CLGeocoder()

@Published var location: CLLocation? = nil
@Published var placemark: CLPlacemark? = nil

override init() {
    super.init()
    self.locationManager.delegate = self
    self.locationManager.desiredAccuracy = kCLLocationAccuracyBest
    self.locationManager.distanceFilter = kCLDistanceFilterNone
    self.locationManager.requestWhenInUseAuthorization()
    self.locationManager.startUpdatingLocation()
    
}

func geoCode(with location: CLLocation) {
    geoCoder.reverseGeocodeLocation(location) { (placemark, error) in
        if error != nil {
            print(error!.localizedDescription)
        } else {
            self.placemark = placemark?.first
        }
    }
}

func startUpdating() {
    self.locationManager.delegate = self
    self.locationManager.requestWhenInUseAuthorization()
    self.locationManager.startUpdatingLocation()
    }
}

extension LocationManager: CLLocationManagerDelegate {

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

ExploreView（启动时显示的第一个视图）

import SwiftUI
import CoreLocation
import Foundation


struct ExploreView: View {
    @ObservedObject  var location = LocationManager()
    @ObservedObject var fetcher: RestaurantFetcher


init() {
    let location = LocationManager()
    self.location = location
    self.fetcher = RestaurantFetcher(locationManager: location)
    self.location.startUpdating()
}

var body: some View {
        ScrollView (.vertical) {
            VStack {
                HStack {
                    Text("Discover ")
                        .font(.system(size: 28))
                        .fontWeight(.bold)
                  +  Text(" \(location.placemark?.locality ?? "")")
                        .font(.system(size: 28))
                        .fontWeight(.bold)
                    Spacer()                       
                }
                HStack {
                    SearchBar(text: .constant(""))
                }.padding(.top, 16)                
                HStack {
                    Text("Featured Restaurants")
                        .font(.system(size: 24))
                        .fontWeight(.bold)
                    Spacer()                       
                    NavigationLink(
                        destination: FeaturedView(),
                        label: {
                            Text("View All")
                        })                        
                }.padding(.vertical, 30)                 
                HStack {
                    Text("All Cuisines")
                        .font(.system(size: 24))
                        .fontWeight(.bold)
                    Spacer()
                }                
                Spacer()
            }.padding()
        }      
    }
}

public class RestaurantFetcher: ObservableObject {
    @Published var businesses = [RestaurantResponse]()
    @ObservedObject var locationManager: LocationManager
    let location = LocationManager()

var lat: String {
    return "\(location.location?.coordinate.latitude ?? 0.0)"
}

var long: String {
    return "\(location.location?.coordinate.longitude ?? 0.0)"
}

init(locationManager: LocationManager) {
    let location = LocationManager()
    self.locationManager = location
    self.location.startUpdating()
    
    load()
}

func load() {
    print("\(location.location?.coordinate.latitude ?? 0.0)")
    print("user latitude top of function")
    //Returns default values of 0.0
    let apikey = "APIKEY Here"
    let url = URL(string: "https://api.yelp.com/v3/businesses/search?latitude=\(lat)&longitude=\(long)&radius=40000")!
    var request = URLRequest(url: url)
    request.setValue("Bearer \(apikey)", forHTTPHeaderField: "Authorization")
    request.httpMethod = "GET"
    
    URLSession.shared.dataTask(with: request) { (data, response, error) in
        do {
            if let d = data {
                print("\(self.location.location?.coordinate.longitude ?? 0.0)")
                let decodedLists = try JSONDecoder().decode(BusinessesResponse.self, from: d)
               
                // Returns actual location coordinates
                DispatchQueue.main.async {
                    self.businesses = decodedLists.restaurants
                }
            } else {
                print("No Data")
            }
        } catch {
            print ("Caught")
        }
    }.resume()
    }
}

Answer 1

尝试以下修改后的代码（我需要进行一些复制，因此请注意 - 可能会出现拼写错误）。

主要思想是订阅 LocationManager 更新的位置发布者以侦听位置的显式变化并仅在位置真正更新而不是 nil 后执行下一个 API 加载。

struct ExploreView: View {
    @ObservedObject  var location: LocationManager
    @ObservedObject var fetcher: RestaurantFetcher
    
    init() {
        let location = LocationManager()  // << use only one instance
        self.location = location
        self.fetcher = RestaurantFetcher(locationManager: location)
        
        self.location.startUpdating()   // << do this only once
    }
    
    var body: some View {
        ScrollView (.vertical) {
            VStack {
                HStack {
                    Text("Discover ")
                        .font(.system(size: 28))
                        .fontWeight(.bold)
                        +  Text(" \(location.placemark?.locality ?? "")")
                        .font(.system(size: 28))
                        .fontWeight(.bold)
                    Spacer()
                }
                HStack {
                    SearchBar(text: .constant(""))
                }.padding(.top, 16)
                HStack {
                    Text("Featured Restaurants")
                        .font(.system(size: 24))
                        .fontWeight(.bold)
                    Spacer()
                    NavigationLink(
                        destination: FeaturedView(),
                        label: {
                            Text("View All")
                        })
                }.padding(.vertical, 30)
                HStack {
                    Text("All Cuisines")
                        .font(.system(size: 24))
                        .fontWeight(.bold)
                    Spacer()
                }
                Spacer()
            }.padding()
        }
    }
}

import Combine

public class RestaurantFetcher: ObservableObject {
    @Published var businesses = [RestaurantResponse]()
    private var locationManager: LocationManager
    
    var lat: String {
        return "\(locationManager.location?.coordinate.latitude ?? 0.0)"
    }
    
    var long: String {
        return "\(locationManager.location?.coordinate.longitude ?? 0.0)"
    }
    
    private var subscriber: AnyCancellable?
    init(locationManager: LocationManager) {
        self.locationManager = locationManager
        
        // listen for available location explicitly
        subscriber = locationManager.$location
            .debounce(for: 5, scheduler: DispatchQueue.main) // wait for 5 sec to avoid often reload
            .receive(on: DispatchQueue.main)
            .sink { [weak self] location in
                guard location != nil else { return }
                self?.load()
            }
    }
    
    func load() {
        print("\(locationManager.location?.coordinate.latitude ?? 0.0)")
        print("user latitude top of function")
        //Returns default values of 0.0
        let apikey = "APIKEY Here"
        let url = URL(string: "https://api.yelp.com/v3/businesses/search?latitude=\(lat)&longitude=\(long)&radius=40000")!
        var request = URLRequest(url: url)
        request.setValue("Bearer \(apikey)", forHTTPHeaderField: "Authorization")
        request.httpMethod = "GET"
        
        URLSession.shared.dataTask(with: request) { (data, response, error) in
            do {
                if let d = data {
                    print("\(self.locationManager.location?.coordinate.longitude ?? 0.0)")
                    let decodedLists = try JSONDecoder().decode(BusinessesResponse.self, from: d)
                    
                    // Returns actual location coordinates
                    DispatchQueue.main.async {
                        self.businesses = decodedLists.restaurants
                    }
                } else {
                    print("No Data")
                }
            } catch {
                print ("Caught")
            }
        }.resume()
    }
}

SwiftUI - 获取用户坐标以传入 API 调用

SwiftUI - Get User's coordinates to pass in API call

core-location

swift

clplacemark

combine