How to round an NSDecimalNumber in swift?

问题

I can't find any resources on this, and I've been trying all sorts of stuff, but nothing works.

According to Apple's documentation, you round an NSDecimalNumber like this:

NSDecimalNumber.decimalNumberByRoundingAccordingToBehavior(<#behavior: NSDecimalNumberBehaviors?#>)

It takes in an NSDecimalNumberBehavior, which I'm unsure how to manipulate since it (1) cannot be initiated into a variable and have it's properties changed, and (2) the roundingMode() method according to the documentation doesn't take any parameters, but Xcode fills in a parameter space for "self".

I'm totally lost on this. Back to the basic question; How can I round an NSDecimalNumber in swift?

Thanks in advance

回答1:

you can do it like that

let x = 5
let y = 2
let total = x.decimalNumberByDividingBy(y).decimalNumberByRoundingAccordingToBehavior( NSDecimalNumberHandler(roundingMode: NSRoundingMode.RoundUp, scale: 0, raiseOnExactness: false, raiseOnOverflow: false, raiseOnUnderflow: false, raiseOnDivideByZero: false))   

回答2:

NSDecimalNumberBehaviors is a protocol and thus cannot be instantiated. You need an object of a class conforming to the protocol. Apple provides the class NSDecimalNumberHandler for this purpose, e.g.:

let handler = NSDecimalNumberHandler(roundingMode: NSRoundingMode.RoundBankers, scale: 0, raiseOnExactness: false, raiseOnOverflow: false, raiseOnUnderflow: false, raiseOnDivideByZero: false)
let rounded = dec.decimalNumberByRoundingAccordingToBehavior(handler)

The scale argument is the number of decimals you want, i.e., 0 rounds to an integer.

回答3:

// get a decimal num from a string

let num = NSDecimalNumber.init(string: numStr)

// create an NSDecimalNumberHandler instance 

let behaviour = NSDecimalNumberHandler(roundingMode:.RoundUp, 
scale: 1, raiseOnExactness: false, 
raiseOnOverflow: false, raiseOnUnderflow: 
false, raiseOnDivideByZero: false)

// pass the handler to the method decimalNumberByRoundingAccordingToBehaviour.

// This is an instance method on NSDecimalNumber that takes an object that
// conforms to the protocol NSDecimalNumberBehaviors, which NSDecimalNumberHandler does!

let numRounded = num.decimalNumberByRoundingAccordingToBehavior(behaviour)

来源：https://stackoverflow.com/questions/31070831/how-to-round-an-nsdecimalnumber-in-swift