如何将 Double 格式化为货币 - Swift 3

我是 Swift 编程新手，我一直在 Xcode 8.2 中创建一个简单的小费计算器应用程序，我在我的 Xcode 中设置了计算IBAction以下。但当我实际运行我的应用程序并输入要计算的金额（例如 23.45）时，它会显示超过 2 位小数。我如何将其格式化为.currency在这种情况下？

@IBAction func calculateButtonTapped(_ sender: Any) {

    var tipPercentage: Double {

        if tipAmountSegmentedControl.selectedSegmentIndex == 0 {
            return 0.05
        } else if tipAmountSegmentedControl.selectedSegmentIndex == 1 {
            return 0.10
        } else {
            return 0.2
        }
    }

    let billAmount: Double? = Double(userInputTextField.text!)

    if let billAmount = billAmount {
        let tipAmount = billAmount * tipPercentage
        let totalBillAmount = billAmount + tipAmount

        tipAmountLabel.text = "Tip Amount: $\(tipAmount)"
        totalBillAmountLabel.text = "Total Bill Amount: $\(totalBillAmount)"
    }
}

如果您想强制货币为 $，您可以使用此字符串初始值设定项：

String(format: "Tip Amount: $%.02f", tipAmount)

如果您希望它完全依赖于设备的区域设置，您应该使用NumberFormatter。这将考虑货币的小数位数以及正确定位货币符号。例如。对于 es_ES 语言环境，双精度值 2.4 将返回“2,40 €”；对于 jp_JP 语言环境，双精度值 2.4 将返回“¥ 2”。

let formatter = NumberFormatter()
formatter.locale = Locale.current // Change this to another locale if you want to force a specific locale, otherwise this is redundant as the current locale is the default already
formatter.numberStyle = .currency
if let formattedTipAmount = formatter.string(from: tipAmount as NSNumber) {
    tipAmountLabel.text = "Tip Amount: \(formattedTipAmount)"
}