无法从 API 解码 JSON 数据
我正在尝试使用从 API 获取的数据更新标签以打印应用程序中的比特币价格和百分比变化,但我不知道如何正确解码 JSON.
I am trying to update labels with data fetched from an API to print Bitcoin price and percentage variation in an app but I can't figure out how to properly decode the JSON.
BitcoinInfo.swift:
BitcoinInfo.swift:
import Foundation
import UIKit
struct Bitcoin: Codable {
let percentChange1h: String
let priceEUR: String
private enum CodingKeys: String, CodingKey {
case percentChange1h = "percent_change_1h", priceEUR = "price_eur"
}
}
extension Bitcoin {
var priceEURdecimal: Decimal {
return Decimal(string: priceEUR) ?? 0
}
var priceEURcurrency: String {
Formatter.currency.locale = Locale(identifier: "fr_FR")
return Formatter.currency.string(for: priceEURdecimal) ?? ""
}
}
ViewController.swift:
ViewController.swift:
import Foundation
import UIKit
class ViewController: UIViewController {
let bitcoinInfoController = BitcoinInfoController()
@IBOutlet weak var bitcoinPriceLabel: UILabel!
@IBOutlet weak var bitcoinPercentageChangeLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
bitcoinPriceLabel.text = ""
bitcoinPercentageChangeLabel.text = ""
fetchBitcoinInfo { bitcoin, error in
guard let bitcoin = bitcoin else {
print(error!);
return
}
self.updateUI(with: bitcoin)
}
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
func updateUI(with bitcoinInfo: Bitcoin) {
DispatchQueue.main.async {
self.bitcoinPriceLabel.text = bitcoinInfo.priceEURcurrency
self.bitcoinPercentageChangeLabel.text = String(format: "%.2f%%", Double(bitcoinInfo.percentChange1h) ?? 0)
}
}
func fetchBitcoinInfo(completion: @escaping (Bitcoin?, Error?) -> Void) {
let baseURL = URL(string: "https://api.coinmarketcap.com/v1/ticker/bitcoin/?convert=EUR")!
let url = baseURL
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else { return }
do {
if let bitcoinEUR = try JSONDecoder().decode([Bitcoin].self, from: data).first {
print(bitcoinEUR)
print(bitcoinEUR.priceEUR)
print(bitcoinEUR.priceEURdecimal)
print(bitcoinEUR.priceEURcurrency)
print(bitcoinEUR.percentChange1h)
completion(bitcoinEUR, nil)
}
} catch {
print(error)
}
}
task.resume()
}
}
控制台打印没有数据返回或数据未正确解码."
The console is printing "Either no data was returned or data was not properly decoded."
这是代码的最新版本.代码现在 100% 可用!:)
This is the latest version of the code. The code is now 100% functional! :)
主要问题是价格和百分比是 Strings 而不是 Doubles.顺便说一句,它返回一个数组,因此您需要在解码时使用 [Bitcoin].self
类型:
The main problem is the price and percentage are Strings not Doubles. Btw it returns an array so you need to use [Bitcoin].self
type when decoding it:
这是您的可编码结构的外观:
This is how your codable struct should look like:
struct Bitcoin: Codable {
let id: String
let name: String
let symbol: String
let rank: String
let priceUSD: String
let priceBTC: String
let volume24hUSD: String
let marketCapUSD: String
let availableSupply: String
let totalSupply: String
let maxSupply: String
let percentChange1h: String
let percentChange24h: String
let percentChange7d: String
let lastUpdated: String
let priceEUR: String
let volume24hEUR: String
let marketCapEUR: String
private enum CodingKeys: String, CodingKey {
case id, name, symbol, rank,
priceUSD = "price_usd",
priceBTC = "price_btc",
volume24hUSD = "24h_volume_usd",
marketCapUSD = "market_cap_usd",
availableSupply = "available_supply",
totalSupply = "total_supply",
maxSupply = "max_supply",
percentChange1h = "percent_change_1h",
percentChange24h = "percent_change_24h",
percentChange7d = "percent_change_7d",
lastUpdated = "last_updated",
priceEUR = "price_eur",
volume24hEUR = "24h_volume_eur",
marketCapEUR = "market_cap_eur"
}
}
这就是你应该如何解码 API 返回的 json 数组并获取它的第一个元素:
And this is how you should decode the json array returned by the API and get its first element:
do {
if let bitcoinEUR = try JSONDecoder().decode([Bitcoin].self, from: data).first {
print(bitcoinEUR)
print(bitcoinEUR.priceEUR)
print(bitcoinEUR.percentChange1h)
}
} catch {
print(error)
}
如果你只对这两个属性感兴趣,你可以像这样设置你的比特币结构:
If you are only interested in those two properties you can set your bitcoin structure like this:
struct Bitcoin: Codable {
let percentChange1h: String
let priceEUR: String
private enum CodingKeys: String, CodingKey {
case percentChange1h = "percent_change_1h", priceEUR = "price_eur"
}
}
编辑/更新:
注意:您正在使用美元货币符号显示欧元价格.如果您需要用 2 个小数位格式化您的欧元价格,您需要首先使用 API 返回的字符串初始化一个新的浮点对象.
Note: You are displaying euro price using the dollar currency symbol. If you need to format your euro price with 2 fraction digits you will need to initialize first a new Floating point object with the string returned by the API.
因此您可以使用两个计算属性扩展比特币 API,一个将欧元价格字符串转换为十进制,另一个将十进制值格式化为货币:
So you can extend the Bitcoin API with two computed properties, one to convert the euro price string to Decimal and the other to format the decimal value into currency:
extension Bitcoin {
var priceEURdecimal: Decimal {
return Decimal(string: priceEUR) ?? 0
}
var priceEURcurrency: String {
Formatter.currency.locale = Locale(identifier: "fr_FR")
return Formatter.currency.string(for: priceEURdecimal) ?? ""
}
}
您还需要将这些扩展添加到项目中的新 Swift 文件中,以帮助您格式化货币:
You will need also to add those extensions to a new Swift file in your project to help you format the currency:
extension NumberFormatter {
convenience init(numberStyle: Style) {
self.init()
self.numberStyle = numberStyle
}
}
extension Formatter {
static let currency = NumberFormatter(numberStyle: .currency)
}
用法:
do {
if let bitcoinEUR = try JSONDecoder().decode([Bitcoin].self, from: data).first {
print(bitcoinEUR.priceEURdecimal) // "13823.952495\n"
print(bitcoinEUR.priceEURcurrency) // "13 823,95 €\
}
} catch {
print(error)
}