Swift Firestore防止检查字典密钥是否存在

我有一段代码，它返回Firestore查询的结果。因为我想确保这些值存在，所以我要检查它们中的每一个，比如

if let driverLat=packageDetails[“driverLat”]as？双重的etc

，也可以铸造它们。这真的很烦人，我想知道是否有更好的解决办法

db.collection("packages").document(documentID).getDocument() { (document, error) in
    if let document = document, document.exists {
        if let packageDetails = document.data() as [String: AnyObject]? {
            if let driverLat = packageDetails["driverLat"] as? Double, let driverLon = packageDetails["driverLon"] as? Double {
                if let destinationLat = packageDetails["destinationLat"] as? Double, let destinationLon = packageDetails["destinationLon"] as? Double {
                    // more code
                }
            }
        }
    }
}

---

我认为您应该使用多个

guard let

语句。这可以防止金字塔形代码降低可读性

看起来是这样的：

typealias Json = [String: AnyObject]

db.collection("packages").document(documentID).getDocument() { (document, error) in
    guard let document       = document, document.exists else { return }
    guard let packageDetails = document.data() as Json? else { return }

    guard let driverLat      = packageDetails["driverLat"] as? Double else { return }
    guard let driverLon      = packageDetails["driverLon"] as? Double else { return }

    guard let destinationLat = packageDetails["destinationLat"] as? Double else { return }
    guard let destinationLon = packageDetails["destinationLon"] as? Double else { return }

    // more code
}