如果你想在逗号后面只有0表示圆，试试这个:

extension Double {
    func isInteger() -> Any {
        let check = floor(self) == self
        if check {
            return Int(self)
        } else {
            return self
        }
    }
}

let toInt: Double = 10.0
let stillDouble: Double = 9.12

print(toInt.isInteger) // 10
print(stillDouble.isInteger) // 9.12

斯威夫特5

使用字符串方法

var yourDouble = 3.12345
//to round this to 2 decimal spaces i could turn it into string
let roundingString = String(format: "%.2f", myDouble)
let roundedDouble = Double(roundingString) //and than back to double
// result is 3.12 

但是使用扩展更容易被接受

extension Double {
    func round(to decimalPlaces: Int) -> Double {
        let precisionNumber = pow(10,Double(decimalPlaces))
        var n = self // self is a current value of the Double that you will round
        n = n * precisionNumber
        n.round()
        n = n / precisionNumber
        return n
    }
}

然后你可以使用:

yourDouble.round(to:2)

在Swift 5.5和Xcode 13.2中:

let pi: Double = 3.14159265358979
String(format:"%.2f", pi)

例子:

附注:自Swift 2.0和Xcode 7.2以来一直如此

如果你想四舍五入Double值，你可能想要使用Swift Decimal，这样你就不会在尝试用这些四舍五入值计算时引入任何可能出现的错误。如果使用Decimal，则它可以准确地表示舍入浮点值的十进制值。

所以你可以这样做:

extension Double {
    /// Convert `Double` to `Decimal`, rounding it to `scale` decimal places.
    ///
    /// - Parameters:
    ///   - scale: How many decimal places to round to. Defaults to `0`.
    ///   - mode:  The preferred rounding mode. Defaults to `.plain`.
    /// - Returns: The rounded `Decimal` value.

    func roundedDecimal(to scale: Int = 0, mode: NSDecimalNumber.RoundingMode = .plain) -> Decimal {
        var decimalValue = Decimal(self)
        var result = Decimal()
        NSDecimalRound(&result, &decimalValue, scale, mode)
        return result
    }
}

然后，你可以像这样得到四舍五入的十进制值:

let foo = 427.3000000002
let value = foo.roundedDecimal(to: 2) // results in 427.30

如果你想用指定的小数位数来显示它(以及为用户的当前语言环境本地化字符串)，你可以使用NumberFormatter:

let formatter = NumberFormatter()
formatter.maximumFractionDigits = 2
formatter.minimumFractionDigits = 2

if let string = formatter.string(for: value) {
    print(string)
}

Lots of example are using maths, the problem is floats are approximations of real number, there is no way to express 0.1 (1/10) exactly as a float just as there is no exact way to express ⅓ exactly using decimal points, so you need to ask your self exactly what your are trying to achieve, if you just want to display them leave them as they are in code, trying to round them is going to justify give you less accurate result as you are throwing away precious, round ⅓ in decimal notation to 1 decimal place is not going to give you a number closer to ⅓, us NumberFormate to round it, if you have something like a viewModel class it can be used to return a string representation to your models numbers. NumberFormaters give you lots of control on how numbers are formatted and the number of decimal places you want.

Swift最佳方式

这就是我把四舍五入到小数点后两位的方法

let val = round(100 * scale) / 100