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)

//find the distance between two points
let coordinateSource = CLLocation(latitude: 30.7717625, longitude:76.5741449 )
let coordinateDestination = CLLocation(latitude: 29.9810859, longitude: 76.5663599)
let distanceInMeters = coordinateSource.distance(from: coordinateDestination)
let valueInKms = distanceInMeters/1000
let preciseValueUptoThreeDigit = Double(round(1000*valueInKms)/1000)
self.lblTotalDistance.text = "Distance is : \(preciseValueUptoThreeDigit) kms"

二重值舍入到小数的x位 不。小数点后的数

var x = 1.5657676754
var y = (x*10000).rounded()/10000
print(y)  // 1.5658 

var x = 1.5657676754 
var y = (x*100).rounded()/100
print(y)  // 1.57 

var x = 1.5657676754
var y = (x*10).rounded()/10
print(y)  // 1.6

这个解决方案对我很有效。XCode 13.3.1 & Swift 5

extension Double {
    
    func rounded(decimalPoint: Int) -> Double {
        let power = pow(10, Double(decimalPoint))
       return (self * power).rounded() / power
    }
}

测试:

print(-87.7183123123.rounded(decimalPoint: 3))
print(-87.7188123123.rounded(decimalPoint: 3))
print(-87.7128123123.rounded(decimalPoint: 3))

结果:

-87.718
-87.719
-87.713

我会用

print(String(format: "%.3f", totalWorkTimeInHours))

然后把。3f改成任何你需要的十进制数

这是一个完整的代码

Swift 3.0/4.0/5.0, Xcode 9.0 GM/9.2及以上

let doubleValue : Double = 123.32565254455
self.lblValue.text = String(format:"%.f", doubleValue)
print(self.lblValue.text)

输出- 123

let doubleValue : Double = 123.32565254455
self.lblValue_1.text = String(format:"%.1f", doubleValue)
print(self.lblValue_1.text)

输出- 123.3

let doubleValue : Double = 123.32565254455
self.lblValue_2.text = String(format:"%.2f", doubleValue)
print(self.lblValue_2.text)

输出- 123.33

let doubleValue : Double = 123.32565254455
self.lblValue_3.text = String(format:"%.3f", doubleValue)
print(self.lblValue_3.text)

输出- 123.326