SWIFT - LocationManager looping through multiple times?

问题

I have a locationManager function to grab the users current location and posting the name of the city and state. I have a print statement so I can check in my console if everything is working properly...and it is. However, it prints the city location 3 times. This actually causes an issue in my actual app but thats beyond the point of this question.

My function is as follows:

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()
        }
    }
}

So in my print(self.usersLocation) it will print in my console three times. Is this normal?

UPDATE TO SHOW 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
}

回答1:

I'd first suggest a few things:

Call stopUpdatingLocation before you perform reverseGeocodeLocation.

You are calling stopUpdatingLocation inside the reverseGeocodeLocation completion handler closure. The problem is that this runs asynchronously, and thus didUpdateLocations may receive additional location updates in the intervening period. And often, when you first start location services, you'll get a number of updates, often with increasing accuracy (e.g. horizontalAccuracy values that are smaller and smaller). If you turn off location services before initiating asynchronous geocode request, you'll minimize this issue.
You can also add add a distanceFilter in viewDidLoad, which will minimize redundant calls to the delegate method:
```
locationManager.distanceFilter = 1000
```

You can use your own state variable that checks to see if the reverse geocode process has been initiated. For example:

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()
    }
}

回答2:

I had the same problem and Rob's answer didn't do it for me.

When the location service first starts, the location is updated multiple times regardless of the distanceFilter.

You might still want the location to be updated and you don't want to lose the location accuracy(which is the whole point of updating location multiple times on start-up), so calling stopUpdatingLocation(or using a local variable) after the first geolocating call isn't the way to go either.

The most intuitive way is to wrap your geocode call in an @objc function and call the the function with a delay:

NSObject.cancelPreviousPerformRequests(withTarget: self)
perform(#selector(myGeocodeFunction(_:)), with: location, afterDelay: 0.5)

来源：https://stackoverflow.com/questions/34033506/swift-locationmanager-looping-through-multiple-times

标签

ios

swift

locationmanager

reversegeocodelocation