Question

我正在尝试使用适用于iOS的Alpha Vantage API构建显示货币汇率的应用。我已经构建了函数，但无法弄清楚如何访问确切的json值，即“ 5. Exchange Rate”。

以下是一些代码和json数据，可以帮助您更好地进行解释：

内置的URL：

workdir: config['workdir']

视图控制器中的行情

func USDtoEUR(_ completionHandler: @escaping (_ success: Bool, _ quotes: [String:AnyObject]?, _ error: String?) -> Void) {

    let urlString = "https://www.alphavantage.co/query?function=CURRENCY_EXCHANGE_RATE&from_currency=USD&to_currency=EUR&apikey=NP3M8LL62YJDO0YX"
        let session = URLSession.shared
        let url = URL(string: urlString)!

        let request = URLRequest(url: url)
        let task = session.dataTask(with: request, completionHandler: { data, response, error in
            if error != nil {
                completionHandler(false, nil, error!.localizedDescription)
            }
            else {
                do {
                    let result = try JSONSerialization.jsonObject(with: data!, options: JSONSerialization.ReadingOptions.allowFragments) as! NSDictionary
                    if let dictionary = result["Realtime Currency Exchange Rate"] as? [String:AnyObject]! {
                        completionHandler(true, dictionary, nil)
                    }
                    else {
                        completionHandler(false, nil, nil)
                    }
                } catch {
                    completionHandler(false, nil, "Unable to process retrieved data.")
                }
            }

        })
        task.resume()

    }

//触摸“ USD”按钮后显示的报价：

func usdQUotesRequest() {

  USDClient().USDtoEUR() { success, newQuote, error in

    if success {
        self.usdtoeurquote = newQuote
        DispatchQueue.main.async {
            self.stopActivityIndicator()
            self.Refresh.isEnabled = true
        }

    } else {
        DispatchQueue.main.async {
            self.displayAlert("Unable to Retrieve Latest Conversion Rates", message: "\(error!)")
            self.stopActivityIndicator()
            self.Refresh.isEnabled = true

        }
    }
}

原始JSON数据：The json data on the webpage

Answer 1

主要错误是键5. Exchange Rate的值为String而不是Float，并且在强行打开包装时，代码可靠地崩溃了。

在Swift 4中，Decodable协议比字典方便得多。

创建两个结构。 ExchangeRate结构包含一个计算属性floatRate以返回Float值

struct Root : Decodable {
    let exchangeRate : ExchangeRate
    private enum  CodingKeys: String, CodingKey { case exchangeRate = "Realtime Currency Exchange Rate" }
}

struct ExchangeRate : Decodable {

    let fromCode, fromName, toCode, toName, rate : String
    let lastRefreshed, timeZone : String

    private enum  CodingKeys: String, CodingKey {
        case fromCode = "1. From_Currency Code"
        case fromName = "2. From_Currency Name"
        case toCode = "3. To_Currency Code"
        case toName = "4. To_Currency Name"
        case rate = "5. Exchange Rate"
        case lastRefreshed = "6. Last Refreshed"
        case timeZone = "7. Time Zone"
    }

    var floatRate : Float {
        return Float(rate) ?? 0.0
    }
}

然后通过将 from 和传递给货币作为参数，使下载功能更加通用。此版本使用JSONDecoder并返回ExchangeRate实例或Error

func downloadRate(from: String, to: String, completionHandler: @escaping (ExchangeRate?, Error?) -> Void) {

    let urlString = "https://www.alphavantage.co/query?function=CURRENCY_EXCHANGE_RATE&from_currency=\(from)&to_currency=\(to)&apikey=NP3M8LL62YJDO0YX"
    let task = URLSession.shared.dataTask(with: URL(string: urlString)!, completionHandler: { data, response, error in
        if error != nil {
            completionHandler(nil, error!)
        } else {
            do {
                let result = try JSONDecoder().decode(Root.self, from: data!)
                completionHandler(result.exchangeRate, nil)
            } catch {
                completionHandler(nil, error)
            }
        }
    })
    task.resume()
}

并使用它

func usdQUotesRequest() {

  USDClient().downloadRate(from:"USD", to: "EUR") { exchangeRate, error in

    if let exchangeRate = exchangeRate {
        self.usdtoeurquote = exchangeRate.floatRate
        DispatchQueue.main.async {
            self.stopActivityIndicator()
            self.Refresh.isEnabled = true
        }
    } else {
        DispatchQueue.main.async {
            self.displayAlert("Unable to Retrieve Latest Conversion Rates", message: "\(error!)")
            self.stopActivityIndicator()
            self.Refresh.isEnabled = true
        }
    }
}

想要查看JSON元数据

1 个答案: