在 Swift 中创建货币转换器

Question

我正在尝试用 Swift 制作货币转换器。我看到了这篇文章：需要API进行货币转换以及如何在Swift中发出HTTP请求？。

因此，当我将它们组合在一起时：

let url = NSURL(string: "http://download.finance.yahoo.com/d/quotes.csv?s=USDEUR=X&f=nl1d1t1");
let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
     println(NSString(data: data, encoding: NSUTF8StringEncoding))
}
task.resume()

它向我返回一个输出，如下所示：

Optional("USD to EUR",0.7987,"11/20/2014","3:45am")

但我想访问货币汇率。我该怎么做？我不知道该怎么做？

Answer 1

我在 Swift 5 中做了一个更简单的货币转换器。如果您有兴趣，请在我的GitHub上查看：https://github.com/ThiagoAM/CurrencyConverter

用法非常简单：

class ViewController: UIViewController {
// Creates the Currency Converter instance:
let currencyConverter = CurrencyConverter()
override func viewDidLoad() {
    super.viewDidLoad()
    // Updates the exchange rates:
    currencyConverter.updateExchangeRates(completion: {
        // The code inside here runs after all the data is fetched.
        // Now you can convert any currency:
        // • Example_1 (USD to EUR):
        let doubleResult = self.currencyConverter.convert(10, valueCurrency: .USD, outputCurrency: .EUR)
        print("••• 10 USD = (doubleResult!) EUR •••")
        // • Example_2 (EUR to GBP) - Returning a formatted String:
        let formattedResult = self.currencyConverter.convertAndFormat(10, valueCurrency: .EUR, outputCurrency: .GBP, numberStyle: .decimal, decimalPlaces: 4)
        print("••• Formatted Result (10 EUR to GBP): (formattedResult!) •••")
    })
}

}

如果你想学习如何制作它，你可以在这里学习 Swift 代码：https://github.com/ThiagoAM/CurrencyConverter/blob/master/CurrencyConverter.swift
它基本上是一个XML解析器，从以下源获取数据：https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml

Answer 2

if let string = NSString(data: data, encoding: NSUTF8StringEncoding) {
    let exchangeRate = string.componentsSeparatedByString(",")[1].doubleValue
}

Answer 3

返回的数据是一个字符串，其中值用逗号分隔，所以这是我的方法：

var dataString = NSString(data: data, encoding: NSUTF8StringEncoding)
let values = dataString.componentsSeparatedByString(",")
let exchangeRate = values[1].doubleValue

Answer 4

Swift 3 版本：我无法获得在 Swift 3 中编译的已接受答案。 以下是我在 swift 3 中能够开始的工作：

    guard let url = URL(string: "https://download.finance.yahoo.com/d/quotes.csv?s=USDEUR=X&f=nl1d1t1") else {
        print("Error: cannot create translation URL")
        return
    }
    let loadRequest = URLRequest(url:url)
    URLSession.shared.dataTask(with: loadRequest, completionHandler: { (data, response, error) in
        if let error = error {
            #if DEBUG
                print("Error: data task error for translation (error)")
            #endif
            return
        }
        guard let data = data else {
            #if DEBUG
                print("Error: data null for translation")
            #endif
            return
        }
        if let translationString = String(data: data, encoding: String.Encoding(rawValue: String.Encoding.utf8.rawValue)) {
            #if DEBUG
                print(translationString)
            #endif
            let exchangeRateArray = translationString.components(separatedBy: ",")
            let exchangeRate: Double = Double(exchangeRateArray[1])!
            print(exchangeRate)
        }
        else {
            #if DEBUG
                print("Error generating string from data in translation")
            #endif
            return
        }
    }).resume()