反向地理编码解释

Question

我在 Swift 4 中找到了一段很棒的反向地理编码代码：Reverse geocoding in Swift 4

我不明白这里发生了什么：

func geocode(latitude: Double, longitude: Double, completion: @escaping (CLPlacemark?, Error?) -> ())  {
CLGeocoder().reverseGeocodeLocation(CLLocation(latitude: latitude, longitude: longitude)) { completion($0?.first, $1) }
}

从这里调用它之后：

geocode(latitude: -22.963451, longitude: -43.198242) { placemark, error in
 guard let placemark = placemark, error == nil else { return }
// you should always update your UI in the main thread
DispatchQueue.main.async {
    //  update UI here
    print("address1:", placemark.thoroughfare ?? "")
    print("address2:", placemark.subThoroughfare ?? "")
    print("city:",     placemark.locality ?? "")
    print("state:",    placemark.administrativeArea ?? "")
    print("zip code:", placemark.postalCode ?? "")
    print("country:",  placemark.country ?? "")       
 }
}

谁能解释一下。

Answer 1

# Gets latitude, longitude and a completion block
func geocode(latitude: Double, longitude: Double, completion: @escaping (CLPlacemark?, Error?) -> ()) 
{
    # Calls system function to resolve the coordinates
    CLGeocoder().reverseGeocodeLocation(CLLocation(latitude: latitude, longitude: longitude))
    {
        # $0 is the placemarks array so this returns the first value of the placemarks array
        # $1 is the error 
        completion($0?.first, $1)

    }
}

Geocode 函数获取纬度和经度以及完成块。它将坐标传递给 CLGeocoder().reverseGeocodeLocation 函数并返回带有完成块的第一个地标。

reverseGeocodeLocation 的方法签名是

func reverseGeocodeLocation(_ location: CLLocation, completionHandler: @escaping CLGeocodeCompletionHandler)

而完成处理程序被定义为

typealias CLGeocodeCompletionHandler = ([CLPlacemark]?, Error?) -> Void

如您所见 [CLPlacemark]？是 CLPlacemarks 的可选数组。