计算双回科学表示法

Question

我是用两个双倍来计算价格的，但是当我输出时，它似乎以科学符号的形式返回给1.785e-05。然而，这不是有意的，我如何确保这个输出用8个小数，而不是科学符号？

码

let price = tickerObj.price ?? 0
let quantity = Double(self.activeTextField.text ?? "0") ?? 0
let value = quantity / price

topValueField.text = "\(value.rounded(toPlaces: 8))"

圆扩展

extension Double {
    /// Rounds the double to decimal places value
    func rounded(toPlaces places:Int) -> Double {
        let divisor = pow(10.0, Double(places))
        return (self * divisor).rounded() / divisor
    }
}

Answer 1

这个数字本身作为科学符号是正确的。如果要向用户显示格式化的数字，则应该是字符串。下面是使用NumberFormatter的工作代码：

extension Double {
    /// Rounds the double to decimal places value
    func rounded(toPlaces places:Int) -> String? {
        let fmt = NumberFormatter()
        fmt.numberStyle = .decimal
        fmt.maximumFractionDigits = places
        return fmt.string(from: self as NSNumber)
    }
}

let price = tickerObj.price ?? 0
let quantity = Double(self.activeTextField.text ?? "0") ?? 0
let value = quantity / price

topValueField.text = "\(value.rounded(toPlaces: 8) ?? "Unknown")"