如何在.observeSingleEvent调用之外访问变量？

Question

我正在尝试访问Firebase中“本机”子级下的数据。我可以访问信息，但不能在分配信息的地方使用本机变量。换句话说，如何在下一个公共函数中访问变量“ native”？

这是我获取信息的代码：

public func fetchNative() {
        
        let userEmail = Auth.auth().currentUser?.email
        
        var safeUserEmail: String? {
            var safeEmail = userEmail?.replacingOccurrences(of: ".", with: "-")
            safeEmail = safeEmail?.replacingOccurrences(of: "@", with: "-")
            safeEmail = safeEmail?.replacingOccurrences(of: " ", with: "")
            return safeUserEmail
        }
        
        ref.child(safeUserEmail ?? "fail-fail-com").observeSingleEvent(of: .value, with: { (snapshot) in
            // Get user value
            let value = snapshot.value as? NSDictionary
            var native = value?["Native"] as? String ?? ""
            // ...
            }) { (error) in
                print(error.localizedDescription)
            }
        }

我想在获取后访问函数中的本机变量。任何帮助将不胜感激。