SWIFT - LocationManager循环多次？

Question

我有一个locationManager函数来获取用户当前位置并发布城市和州的名称.我有一个打印声明,所以我可以在我的控制台检查一切是否正常工作......就是这样.但是,它打印城市位置3次.这实际上在我的实际应用程序中引起了一个问题,但这超出了这个问题的范围.

我的功能如下:

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()
        }
    }
}

因此,在我的print(self.usersLocation)中,它将在我的控制台中打印三次.这是正常的吗？

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更新显示视图

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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

我首先建议一些事情:

1. stopUpdatingLocation在表演之前打电话reverseGeocodeLocation.

   您正在完成处理程序关闭stopUpdatingLocation内部调用reverseGeocodeLocation.问题在于它以异步方式运行,因此didUpdateLocations可能在中间期间接收额外的位置更新.通常,当您第一次启动位置服务时,您将获得许多更新,通常会提高准确性(例如,horizontalAccuracy值越来越小).如果在启动异步地理编码请求之前关闭位置服务,则可以最大限度地减少此问题.

2. 您还可以添加添加distanceFilter中viewDidLoad,将尽量减少对委托方法重复的调用:

   locationManager.distanceFilter = 1000
   

3. 您可以使用自己的状态变量来检查是否已启动反向地理编码过程.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()
       }
   }