我想使用不带可选扩展名的String值。我使用以下代码从firebase解析此数据：

Database.database().reference(withPath:
    "Locations").child("Cities").observe(.value, with: { (snapShot) in
        if snapShot.exists() {
            let array:NSArray = snapShot.children.allObjects as NSArray

            for child in array {
                let snap = child as! DataSnapshot

                let cityName = snap.key
                let cityNameString = "\(cityName)"
                if snap.value is NSDictionary {
                    let data:NSDictionary = snap.value as! NSDictionary
                    let lat = data.value(forKey: "lat")
                    let lng = data.value(forKey: "lng")
                    let radius = data.value(forKey: "radius")
                    let latstring = "\(lat)"
                    let lngstring = "\(lng)" 
                    let radiusstring = "\(radius)"

                    let city = CityObject(name: cityNameString , lat: latstring , lng: lngstring, radius: radiusstring)
                    print("Value is", laststring)  
                    self.selectCity(cityObject: city)
                }

            }
        }
    })

解析此数据后，我尝试打印例如latstring并得到以下结果：

值是可选的（52.523553）

我的CityObject如下所示：

class CityObject{
var name: String?
var lat: String?
var lng: String?
var radius: String?

init(name: String?, lat: String?, lng: String?, radius: String?){
    self.name = name
    self.lat = lat
    self.lng = lng
    self.radius = radius
}