从 Firebase 检索用户纬度和经度后添加注释

Question

在从 Firebase 检索到所有在线用户的纬度和经度后，我正在尝试添加所有在线用户的 mapView 注释。我可以将其打印为可选或 CLLocationDegrees aka Double，但是当我尝试将其添加到我的 user.userAnnotation 属性中时，我得到了一个致命错误。这就是我要打印的内容：

this is the users lat Optional(19.435477800000001) 
this is the user latitude in CLLocationDegrees 19.4354778 
fatal error: unexpectedly found nil while unwrapping an Optional value

这是我的功能：

func fetchOnlineUsers() {
    ref = FIRDatabase.database().reference()

    FIRDatabase.database().reference().child("users").observe(.childAdded, with: { (snapshot) in

        if let dictionary = snapshot.value as? [String: AnyObject] {
            let user = AppUser()
            user.userEmail = (snapshot.value as? NSDictionary)?["name"] as? String
            user.latitude = (snapshot.value as? NSDictionary)?["latitude"] as? Double
            user.longitude = (snapshot.value as? NSDictionary)?["longitude"] as? Double
            user.online = ((snapshot.value as? NSDictionary)?["online"] as? Bool)!
            print("this is the user latitude \(user.latitude)")
            let userLat = CLLocationDegrees(user.latitude!)
            let userLon = CLLocationDegrees(user.longitude!)  

            if user.online == true {
                user.userAnnotation.coordinate = CLLocationCoordinate2D(latitude: userLat, longitude: userLon)

                self.users.append(user)
            }
            print("this are the users \(self.users)")
            print("this is the dictionary \(dictionary)")

            self.mainMapView.addAnnotations([user.userAnnotation])
        }
    }, withCancel: nil)
}

Answer 1

嗯，你得到的一些价值是nil。试试这个：

guard let dictionary = snapshot.value as? [String: AnyObject],
let email = (snapshot.value as? NSDictionary)?["name"] as? String,
let latitude = (snapshot.value as? NSDictionary)?["latitude"] as? Double,
let longitude = (snapshot.value as? NSDictionary)?["longitude"] as? Double,
let online = ((snapshot.value as? NSDictionary)?["online"] as? Bool)! else { // Some error }

如果成功，您可以开始使用在 guard let 中创建的变量，它们将 1：有值，2：不是可选的。