从城市名称获取地理位置

Posted 2023-03-11

【中文标题】从城市名称获取地理位置

【英文标题】：Get geo location from city name

【发布时间】：2021-07-16 18:12:09

【问题描述】：

我编写了在文本字段中输入时显示城市名称的代码。我可以使用 For Each 循环显示搜索结果。我需要单击其中一个结果并获取城市名称的地理位置。现在我正在努力从该城市名称中获取地理位置（纬度，经度）。是否有解决方案可以将其实现到我的代码中？

class LocationService: NSObject, ObservableObject 

enum LocationStatus: Equatable 
    case idle
    case noResults
    case isSearching
    case error(String)
    case result


@Published var queryFragment: String = ""
@Published private(set) var status: LocationStatus = .idle
@Published private(set) var searchResults: [MKLocalSearchCompletion] = []

private var queryCancellable: AnyCancellable?
private let searchCompleter: MKLocalSearchCompleter!

init(searchCompleter: MKLocalSearchCompleter = MKLocalSearchCompleter()) 
    self.searchCompleter = searchCompleter
    super.init()
    self.searchCompleter.delegate = self

    queryCancellable = $queryFragment
        .receive(on: DispatchQueue.main)
        // we're debouncing the search, because the search completer is rate limited.
        // feel free to play with the proper value here
        .debounce(for: .milliseconds(250), scheduler: RunLoop.main, options: nil)
        .sink(receiveValue:  fragment in
            self.status = .isSearching
            if !fragment.isEmpty 
                self.searchCompleter.queryFragment = fragment
             else 
                self.status = .idle
                self.searchResults = []
            
    )



extension LocationService: MKLocalSearchCompleterDelegate 
func completerDidUpdateResults(_ completer: MKLocalSearchCompleter) 

    // out a lot of places and only shows cities and countries.
    self.searchResults = completer.results.filter( $0.subtitle == "" )
    self.status = completer.results.isEmpty ? .noResults : .result


func completer(_ completer: MKLocalSearchCompleter, didFailWithError error: Error) 
    self.status = .error(error.localizedDescription)

【参考方案1】：

CoreLocation 框架为您提供CLGeocoder，它可以尝试在坐标和地名之间双向转换。

您可以在 Playground 中尝试一下，看看它是如何工作的：

import Foundation
import CoreLocation

func getCoordinate( addressString : String,
                    completionHandler: @escaping(CLLocationCoordinate2D, NSError?) -> Void ) 
    let geocoder = CLGeocoder()
    geocoder.geocodeAddressString(addressString)  (placemarks, error) in
        if error == nil 
            if let placemark = placemarks?[0] 
                let location = placemark.location!

                completionHandler(location.coordinate, nil)
                return
            
        

        completionHandler(kCLLocationCoordinate2DInvalid, error as NSError?)
    


let valid = "New Orleans, Louisiana, USA"
let invalid = "The Moon"

getCoordinate(addressString: valid)  location, error in
    guard error == nil else print("Error:"); return

    print(location)


getCoordinate(addressString: invalid)  location, error in
    guard error == nil else print("Error:"); return

    print(location)

结果是异步返回的，因此您需要提供一个完成处理程序。

【讨论】：

谢谢！这对我有帮助。你知道如何在视图中实现 getCoordinate 吗？如果我尝试将 getCoordinate(...) 实现到我的视图中，使用 for each ist 会给我这个错误“包含控制流语句的闭包不能与结果生成器'CommandsBuilder'一起使用”

这是进入视图模型的那种东西。另外，请注意，您不能在短时间内对 API 进行多次调用，它会受到 Apple 的速率限制。