Coinbase API现货，买入和卖出不同货币的价格

Question

我正在使用Coinbase API来获取比特币的现货，买卖价格。我添加了一个包含所有支持货币的选择器视图，当我更改货币时，现货价格会发生变化，但买入和卖出的价格却没有变化。这是我的代码，不知道为什么不工作......

@IBOutlet weak var btcSpotPrice: UILabel!
@IBOutlet weak var btcBuyPrice: UILabel!
@IBOutlet weak var btcSellPrice: UILabel!
@IBOutlet weak var selectedCurrency: UIButton!
@IBOutlet weak var currencyPicker: UIPickerView!
var currencies: [CoinbaseCurrency]?

func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int)
{
    self.selectedCurrency.setTitle(currencies?[row].iso, for: .normal)
    getSpotPrice()
    getBuyPrice()
    getSellPrice()
}

func getSpotPrice()
{
    Coinbase().getSpotRate(withCurrency: self.selectedCurrency.currentTitle) { (spotPrice: CoinbaseBalance?, error: Error?) in
        if let error = error
        {
            let alert = UIAlertController(title: "Error", message: error.localizedDescription, preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
            alert.present(alert, animated: true, completion: nil)
        }
        else
        {
            self.btcSpotPrice.text = spotPrice!.amount! + " " + spotPrice!.currency!
        }
    }
}

func getBuyPrice()
{
    Coinbase().getBuyPrice(withQuantity: "1", currency: "GBP") { (btc: CoinbaseBalance?, fees: [Any]?, subtotal: CoinbaseBalance?, total: CoinbaseBalance?, error: Error?) in

        if let error = error
        {
            let alert = UIAlertController(title: "Error", message: error.localizedDescription, preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
            alert.present(alert, animated: true, completion: nil)
        }
        else
        {
            self.btcBuyPrice.text = total!.currency!
        }
    }
}

func getSellPrice()
{
    Coinbase().getSellPrice(withQuantity: "1", currency: self.selectedCurrency.currentTitle) { (btc: CoinbaseBalance?, fees: [Any]?, subtotal: CoinbaseBalance?, total: CoinbaseBalance?, error: Error?) in

        if let error = error
        {
            let alert = UIAlertController(title: "Error", message: error.localizedDescription, preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
            alert.present(alert, animated: true, completion: nil)
        }
        else
        {
            self.btcSellPrice.text = total!.amount!
        }
    }
}

在我的getBuyPrice方法中，即使将货币硬编码为“GBP”英镑，btcBuyPrice标签仍显示美元。它适用于spotPrice方法，但不适用于买卖价格。