ios - SWIFT - LocationManager 循环多次？

Question

我有一个 locationManager 函数来获取用户的当前位置并发布城市和州的名称。我有一个打印语句，所以我可以检查我的控制台是否一切正常……确实如此。但是，它打印了 3 次城市位置。这实际上会导致我的实际应用程序出现问题，但这超出了这个问题的重点。

我的函数如下:

var usersLocation: String!

var locationManager: CLLocationManager!

func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {

    let userLocation: CLLocation = locations[0]


    CLGeocoder().reverseGeocodeLocation(userLocation) { (placemarks, error) -> Void in

        if error != nil {

            print(error)

        } else {

            let p = placemarks?.first // ".first" returns the first element in the collection, or nil if its empty
            // this code above will equal the first element in the placemarks array

            let city = p?.locality != nil ? p?.locality : ""
            let state = p?.administrativeArea != nil ? p?.administrativeArea : ""

            self.navigationBar.title = ("\(city!), \(state!)")
            self.usersLocation = ("\(city!), \(state!)")
            self.locationManager.stopUpdatingLocation()
            print(self.usersLocation)
            self.refreshPosts()
        }
    }
}

所以在我的 print(self.usersLocation) 中，它将在我的控制台中打印三次。这正常吗？

---

更新以显示 VIEWDIDLOAD

---

override func viewDidLoad() {
    super.viewDidLoad()

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

    self.tableView.rowHeight = UITableViewAutomaticDimension
    self.tableView.estimatedRowHeight = 250.0
}

Answer 1

我首先建议几件事:

1. 在执行 reverseGeocodeLocation 之前调用 stopUpdatingLocation。

   您正在 reverseGeocodeLocation 完成处理程序闭包内调用 stopUpdatingLocation。问题在于它是异步运行的，因此 didUpdateLocations 可能会在其间接收到额外的位置更新。通常，当您第一次启动位置服务时，您会获得许多更新，而且精度通常会越来越高(例如，horizo​​ntalAccuracy 值越来越小)。如果您在启动异步地理编码请求之前关闭位置服务，您将最大限度地减少此问题。

2. 您还可以在 viewDidLoad 中添加一个 distanceFilter，这将最大限度地减少对委托(delegate)方法的冗余调用:

   locationManager.distanceFilter = 1000
   

3. 您可以使用自己的状态变量来检查反向地理编码过程是否已启动。例如:

   private var didPerformGeocode = false
   
   func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
       // if we don't have a valid location, exit
   
       guard let location = locations.first where location.horizontalAccuracy >= 0 else { return }
   
       // or if we have already searched, return
   
       guard !didPerformGeocode else { return }
   
       // otherwise, update state variable, stop location services and start geocode
   
       didPerformGeocode = true
       locationManager.stopUpdatingLocation()
   
       CLGeocoder().reverseGeocodeLocation(location) { placemarks, error in
           let placemark = placemarks?.first
   
           // if there's an error or no placemark, then exit
   
           guard error == nil && placemark != nil else {
               print(error)
               return
           }
   
           let city = placemark?.locality ?? ""
           let state = placemark?.administrativeArea ?? ""
   
           self.navigationBar.title = ("\(city), \(state)")
           self.usersLocation = ("\(city), \(state)")
           print(self.usersLocation)
           self.refreshPosts()
       }
   }