Swift Firestore 阻止检查字典键是否存在

Question

我有这段代码，它返回 Firestore 查询的结果。因为我想确保这些值存在，所以我正在检查其中的每一个值，例如 if let driverLat = packageDetails["driverLat"] as? Double.. 等 并转换它们。这真的很烦人，我想知道是否有更好的解决方案？

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
                }
            }
        }
    }
}

Answer 1

我想说您应该使用多个 guard-let 语句。这可以防止金字塔形代码降低可读性。

看起来像这样:

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
}