SWIFT 4.1 无法使用类型为“（字符串？）”的参数列表调用类型“Double”的初始化程序

Question

我正在检索发布在 Firebase 中的 mapView 注释以在地图上显示它们，但是在转换纬度和经度的字符串值以将它们重新组合成 CLLocationCoordinates2D 时出现错误。我不明白为什么，因为在另一个函数中我使用相同的方法但从数组中获取值但我没有得到错误。同样在检索数据时，我还想使用来自 firebase 的键值作为我的注释的初始化程序。但是我又收到两个错误 Use of unresolved identifier 'firebaseKey' 和 Use of unresolved identifier 'recombinedCoordinate' for initialisers。函数如下：

func displayAlerts() {
        // FIREBASE: Reference
        ref = Database.database().reference()

        // FIREBASE:Retrieve posts and listen for changes
        databaseHandle = ref?.child("Community").child("Alert Notifications").observe(.childAdded, with: { (snapshot) in

            let data = snapshot.value as? [String:String]
            if let actualData = data {
                let dataLatitude = data!["Latitude"]
                let dataLongitude = data!["Longitude"]
                self.alertIconToDisplay = data!["Description"]

                let doubledLatitude = Double(dataLatitude)
                let doubledLongitude = Double(dataLongitude)
                var recombinedCoordinate = CLLocationCoordinate2D(latitude: doubledLatitude!, longitude: doubledLongitude!)
                print("Firebase post retrieved !")
                self.dummyFunctionToFoolFirebaseObservers()
            }
            let dataKey = snapshot.key as? String
            if let firebaseKey = dataKey {
                print("Longitude DataKey is \(String(describing: dataKey))")
                print("Longitude Actual DataKey is \(String(describing: firebaseKey))")

                self.dummyFunctionToFoolFirebaseObservers()
            }

            print("fir long \((snapshot.value!, snapshot.key))")
            userAlertAnnotation = UserAlert(type: self.alertIconToDisplay, coordinate: recombinedCoordinate, firebaseKey: firebaseKey)
            self.mapView.addAnnotation(self.userAlertAnnotation)  
        })
    } 

这是注释模型：

class UserAlert: NSObject , MKAnnotation {
    var type: String?
    var firebaseKey: String?
    var coordinate:CLLocationCoordinate2D

    init(type:String, coordinate:CLLocationCoordinate2D, firebaseKey: String) {
        self.type = type
        self.firebaseKey = firebaseKey
        self.coordinate = coordinate
    }
}

我在这里做错了什么？我知道初始化器上的错误是因为初始化发生在键闭包中，但是我如何将所有数据合并到初始化器中？

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {

        let annotationView = MKAnnotationView(annotation: userAlertAnnotation, reuseIdentifier: "")    //  CHANGE FOR NEW ANNOTATION : FULL DATA

        //added if statement for displaying user location blue dot
        if annotation is MKUserLocation{
            return nil
        } else {


            annotationView.image = UIImage(named: alertIconToDisplay!)                        //    choose the image to load

            let transform = CGAffineTransform(scaleX: 0.27, y: 0.27)
            annotationView.transform = transform
            return annotationView
        }
    }



 func postAlertNotification() {

        // to set next notification id as the position it will have in array ( because first position is 0 ) we use the array.count as value


        let latitude = alertNotificationLatitude
        let longitude = alertNotificationLongitude
        let alertType = alertNotificationType

        let post: [String:String] = [//"Date" : date as! String,
                                     //"Time" : time as! String,
                                     "Latitude" : latitude as! String,
                                     "Longitude" : longitude as! String,
                                     "Description" : alertType as! String]

        var ref: DatabaseReference!
        ref = Database.database().reference()
        ref.child("Community").child("Alert Notifications").childByAutoId().setValue(post)
  }

Answer 1

主题中的错误表明您无法从可选字符串创建 Double，这是真的。
要解决它，请强制解开 Latitude 和 Longitude 的值。

但主要问题是范围问题，初始化程序中使用的所有变量都必须在相同范围内。您可以使用guard 语句展平范围：

...
databaseHandle = ref?.child("Community").child("Alert Notifications").observe(.childAdded, with: { (snapshot) in

        defer { self.dummyFunctionToFoolFirebaseObservers() }
        guard let data = snapshot.value as? [String:String] else { return }
        guard let firebaseKey = snapshot.key as? String else { return }

        //                let date = data!["Date"]
        //                let time = data!["Time"]
        let dataLatitude = data["Latitude"]!
        let dataLongitude = data["Longitude"]!
        self.alertIconToDisplay = data["Description"]!

        let doubledLatitude = Double(dataLatitude)
        let doubledLongitude = Double(dataLongitude)
        let recombinedCoordinate = CLLocationCoordinate2D(latitude: doubledLatitude!, longitude: doubledLongitude!)

        print("Firebase post retrieved !")

        //                self .keyaLon = dataKey
        //                self.keyaLonArray.append(firebaseKey)

        print("Longitude Actual DataKey is \(String(describing: firebaseKey))")

        print("fir long \((snapshot.value!, snapshot.key))")
        self.userAlertAnnotation = UserAlert(type: self.alertIconToDisplay, coordinate: recombinedCoordinate, firebaseKey: firebaseKey)
        self.mapView.addAnnotation(self.userAlertAnnotation)


    })