swift - 使用 swift 按位置从 firebase 获取帖子

Question

我正在尝试获取帖子并在用户进入帖子的某种半径时将它们打印到控制台。我怎样才能 swift 做到这一点。

Answer 1

这是我在 Swift 中编写的一个小结构，让您使用 Haversine formula 计算两个坐标之间的距离(以公里为单位) .

例子

let london = Coordinate(long: -0.118092, lat: 51.509865)
let paris = Coordinate(long: 2.3522219, lat: 48.856614)

print(london.distance(to: paris)) // ~343.43km
print(london == paris) // false
print(london) // 51.509865,-0.118092
print(paris) // 48.856614,2.3522219

代码

import Foundation

public struct Coordinate: CustomStringConvertible, Equatable {
  // Earth radius in km
  private static let radiusEarth = 6371.0

  public typealias Distance = Double

  public let lon: Double
  public let lat: Double

  public init(long: Double, lat: Double) {
    self.lon = long
    self.lat = lat
  }

  public static func == (lhs: Coordinate, rhs: Coordinate) -> Bool {
    return lhs.lon == rhs.lon && lhs.lat == rhs.lat
  }

  public var description: String {
    return "\(lat),\(lon)"
  }

  // Haversine formula
  public func distance(to other: Coordinate) -> Distance {
    let dLat = deg2rad(other.lat - lat)
    let dLon = deg2rad(other.lon - lon)
    let a =
      sin(dLat / 2) * sin(dLat / 2) +
      cos(deg2rad(lat)) * cos(deg2rad(other.lat)) *
      sin(dLon / 2) * sin(dLon / 2)
    let c = 2 * atan2(sqrt(a), sqrt(1 - a))
    return Coordinate.radiusEarth * c
  }

  private func deg2rad(_ deg: Double) -> Double {
    return deg * (.pi / 180.0)
  }
}