委托在类中调用后返回 nil

Question

我正在使用此类获取位置并将其与委托一起发送到另一个视图控制器，但委托在调用时返回 nil。 我的班级：

protocol LocationUpdateProtocol {
    func locationDidUpdateToLocation(location : CLLocation)
}
/// Notification on update of location. UserInfo contains CLLocation for key "location"
let kLocationDidChangeNotification = "LocationDidChangeNotification"
class LocationServiceHelper:NSObject,CLLocationManagerDelegate {

    static let sharedManager = LocationServiceHelper()
    private let locationManager = CLLocationManager()
    var currentLocation:CLLocation?
    weak var delegate :LocationUpdateProtocol?
    private override init() {
        super.init()
        self.locationManager.delegate = self
        locationManager.desiredAccuracy = kCLLocationAccuracyBest
        locationManager.distanceFilter = kCLLocationAccuracyHundredMeters
        locationManager.requestAlwaysAuthorization()
        locationManager.startUpdatingLocation()
    }

    // MARK: CLLocationManagerDelegate

    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard let delegate = self.delegate else {
            return
        }
        currentLocation = locations.first
        let userInfo:NSDictionary = ["location":currentLocation!]
        delegate.locationDidUpdateToLocation(location: currentLocation!)
        NotificationCenter.default.post(name: NSNotification.Name(rawValue: kLocationDidChangeNotification), object: self, userInfo: userInfo as? [AnyHashable : Any])
    }
}

我在下面的另一个类中调用了委托：

var locationServiceReference = LocationServiceHelper.sharedManager
    override func viewDidLoad() {
        super.viewDidLoad()
        fillFields()
      locationServiceReference.delegate = self
        self.mapView.showsUserLocation = true
    }

func locationDidUpdateToLocation(location: CLLocation) {
       // print(location)
        // let myLocation = CLLocationCoordinate2D(latitude: location.coordinate.latitude, longitude: location.coordinate.longitude)
        let myLocationForTesting = CLLocationCoordinate2D(latitude: 33.410165, longitude: 35.480060)
        myLocation = location
            let region = MKCoordinateRegion(center: myLocationForTesting, span: MKCoordinateSpan(latitudeDelta: 0.01, longitudeDelta: 0.01))
        self.mapView.setRegion(region, animated: true)

    }

在更新位置中，委托返回 nil，知道发生了什么吗？该函数未被调用，因为委托返回 nil。

Answer 1

1. 确保您的控制器仍在内存中
2. 您不需要使用防护。可选链在这种情况下效果更好：

func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
    currentLocation = locations.first
    let userInfo:NSDictionary = ["location":currentLocation!]
    delegate?.locationDidUpdateToLocation(location: currentLocation!)
    NotificationCenter.default.post(name: NSNotification.Name(rawValue: kLocationDidChangeNotification), object: self, userInfo: userInfo as? [AnyHashable : Any])
}

1. 确保在委托设置后调用func locationManager(_:didUpdateLocations)。
2. 对于将来，您希望在委托更改为时传递最后一个位置：

weak var delegate :LocationUpdateProtocol? {
    didSet { 
        guard let last = currentLocation else { return }
        delegate?.locationDidUpdateToLocation(location: last)
    }
}

5. 由于它是只有 1 个委托的单例，因此请确保您没有将委托设置为 nil 或其他地方的其他短期对象

Answer 2

这段代码 -

var locationServiceReference = LocationServiceHelper.sharedManager

在您的delegate 设置之前执行，这就是为什么delegate 总是返回nil。

替换

var locationServiceReference = LocationServiceHelper.sharedManager

有

var locationServiceReference : LocationServiceHelper!

并在viewDidLoad() 被调用后初始化。

override func viewDidLoad() {
    super.viewDidLoad()

    locationServiceReference = LocationServiceHelper.sharedManager
    locationServiceReference.delegate = self

}

希望它能帮助你。如果您仍有任何问题，请告诉我。