问为什么我的数组不存储从我的防火墙数据库中检索的值？

EN

func retrieveUsers() {
    let ref = FIRDatabase.database().reference()
    ref.child("users").queryOrderedByKey().observeSingleEvent(of: .value, with: { snapshot in

        let users = snapshot.value as! [String : AnyObject]
        self.allUsers.removeAll()
        for (_, value) in users {

            if let uid = value["uid"] as? String {
                if uid != FIRAuth.auth()!.currentUser!.uid {
                    if let name = value["name"] as? String, let age = value["birthdate"] as? String {
                        let calculatedAge = self.calcAge(birthdate: age)

                        let userToShow = User(name: name,age: calculatedAge)
                        print(userToShow.Name)
                        self.allUsers.append(userToShow)

                    }

                    }
                }
            }
        })
    print(allUsers.count)
    ref.removeAllObservers()


}