swift - 从 Firebase 读取数据时发生类型转换错误

Question

我正在使用mapkit制作一个应用程序，当我尝试从firebase获取用户位置时，它会导致这三行出现错误

let dict = recipeSnap.value as! [String:Double?]

let latitude = dict["latitude"] as? Double?

let longitude = dict["longitude"] as? Double?.

我尝试用字符串替换 double ，但发生了新错误，然后我尝试用 AnyObject 替换它，它有效，但数据类似于可选(37.785834)。当我使用 AnyObject 数据做其他事情时，它总是会导致错误。

这是我的代码

@objc func updateTimer(){

    print("Update location")
    let location = locman.location!.coordinate
    lat = String(location.latitude)
    long = String(location.longitude)
    print(lat)
    print(long)
    let ref = Database.database().reference()
    ref.child("location/User1/longitude").setValue(long)
    ref.child("location/User1/latitude").setValue(lat)
    ref.child("location").observeSingleEvent(of: .value) { (snapshot) in
          self.usern = snapshot.childrenCount
          for snap in snapshot.children{
              let aSnap = snap as! DataSnapshot  
              let dict = aSnap.value as! [String:Double?]
              let latitude = dict["latitude"] as? Double?
              let longitude = dict["longitude"] as? Double?
              print(dict)
              print(latitude)
              print(longitude)

              let point = MKPointAnnotation()
              point.title = "user"
            //point.coordinate = CLLocationCoordinate2D(latitude: CLLocationDegrees(latitude), longitude: CLLocationDegrees(longitude))
              self.mapView.addAnnotation(point)
        }
    }
}

这是我的错误

Could not cast value of type 'Swift._NSContiguousString' (0x1032681f8) to 'NSNumber' (0x1b7a1abf0). 2019-10-10 20:24:05. mapkitMap[1468:709956] Could not cast value of type 'Swift._NSContiguousString' (0x1032681f8) to 'NSNumber' (0x1b7a1abf0). Optional(37.785834)

当我尝试用字符串替换 Double 时，出现新错误

Could not cast value of type '__NSCFNumber' (0x1b7a0e0e0) to 'NSString' (0x1b7a1aad8). 2019-10-10 20:20:32.1 mapkitMap[1465:708355] Could not cast value of type '__NSCFNumber' (0x1b7a0e0e0) to 'NSString' (0x1b7a1aad8).

Answer 1

您似乎将一些纬度和经度存储为字符串值，

lat = String(location.latitude)
long = String(location.longitude)

因此您不能简单地从数据库中将它们作为数字检索。您需要从数据库中将它们作为字符串读取，然后解析它们的数值。

类似于:

  let aSnap = snap as! DataSnapshot  
  let latitude = Double(snap.childSnapshot(forPath: "latitude").value)
  let longitude =  Double(snap.childSnapshot(forPath: "longitude").value)