ios - 解码 API 数据

Question

我正在尝试从 API 获取数据，但无法正确获取，我不知道这里的问题:

struct BTCData : Codable {
    let close : Double
    let high : Double
    let low : Double

    private enum CodingKeys : Int, CodingKey {
        case close = 3
        case high = 4
        case low = 5
    }
}

func fetchBitcoinData(completion: @escaping (BTCData?, Error?) -> Void) {
    let url = URL(string: "https://api.bitfinex.com/v2/candles/trade:30m:tBTCUSD/hist")!

    let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
        guard let data = data else { return }
        do {
            if let bitcoin = try JSONDecoder().decode([BTCData].self, from: data).first {
                print(bitcoin)
                completion(bitcoin, nil)
            }
        } catch {
            print(error)
        }
    }
    task.resume()
}

我希望能够在每个 dict 中访问 close 并像这样迭代:

var items : BTCData!

for idx in 0..<15 {
    let diff = items[idx + 1].close - items[idx].close
    upwardMovements.append(max(diff, 0))
    downwardMovements.append(max(-diff, 0))
}

我得到 nil。我不明白如何解码这种 API，我需要迭代不在另一个 dict 中的东西。

编辑:以上问题已解决，我现在正努力在另一个函数中使用 [BTCData]。

我在这里尝试使用它:

func fetchBitcoinData(completion: @escaping ([BTCData]?, Error?) -> Void) {

    let url = URL(string: "https://api.bitfinex.com/v2/candles/trade:30m:tBTCUSD/hist")!

    let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
        guard let data = data else {
            completion(nil, error ?? FetchError.unknownNetworkError)
            return
        }
        do {
            let bitcoin = try JSONDecoder().decode([BTCData].self, from: data); completion(bitcoin, nil)
            //let close52 = bitcoin[51].close
            //print(bitcoin)
            //print(close52)
        } catch let parseError {
            completion(nil, parseError)
        }
    }
    task.resume()
}
class FindArray {

    var items = [BTCData]()

    func findArray() {
        let close2 = items[1].close
        print(close2)
    }
}

fetchBitcoinData() { items, error in
    guard let items = items,
        error == nil else {
            print(error ?? "Unknown error")
            return
    }
    let call = FindArray()
    call.items = items
    call.findArray()
}

编辑 2:使用 [BTCData]() 解决。 var items : [BTCData] = [] 也有效

Answer 1

要使用 Decodable 将数组数组解码为结构，您必须使用 unkeyedContainer。由于没有字典，CodingKeys 没有用。

struct BTCData : Decodable {
    let timestamp : Int 
    let open, close, high, low, volume : Double

    init(from decoder: Decoder) throws {
        var container = try decoder.unkeyedContainer()
        timestamp = try container.decode(Int.self)
        open = try container.decode(Double.self)
        close = try container.decode(Double.self)
        high = try container.decode(Double.self)
        low = try container.decode(Double.self)
        volume = try container.decode(Double.self)
    }
}

您不必更改 JSONDecoder() 行。

...
if let bitcoin = try JSONDecoder().decode([BTCData].self, from: data).first {
   print(bitcoin)
   completion(bitcoin, nil)
}

---

只需添加两行，甚至可以将时间戳解码为Date 值

struct BTCData : Decodable {
    let timestamp : Date
    let open, close, high, low, volume : Double

    init(from decoder: Decoder) throws {
        var container = try decoder.unkeyedContainer()
        timestamp = try container.decode(Date.self)
...

---

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .millisecondsSince1970
if let bitcoin = try decoder.decode([BTCData].self, from: data).first {
    print(bitcoin)
    completion(bitcoin, nil)
}

---

解码数组并获取特定索引处的值

do {
    let bitcoins = try JSONDecoder().decode([BTCData].self, from: data)
    let close52 = bitcoins[51].close
    print(close52)
...