Swift:正确解码不精确的小数

本文介绍了Swift:正确解码不精确的小数的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我需要从这个问题我知道如何正确处理Decimal实例，但是在解码时该如何做呢?

I need to decode (Decodable protocol) an imprecise decimal value correctly, from this question I understand how to properly handle the Decimal instantiation, but how can I do this when decoding?

如果尝试将任何数字初始化为字符串

If trying to init any number as a String

if let value = try! container.decode(String.self, forKey: .d) { self.taxAmount = Decimal(string: value) }

我得到Fatal Error: "Expected to decode String but found a number instead."

如果尝试将130.43初始化为小数

And if try to init 130.43 as a Decimal

if let value = try! container.decode(Decimal.self, forKey: .d) { //value.description is 130.43000000000002048 self.d = Decimal(string: value.description) //making subtotal to be also 130.43000000000002048 and not 130.43 }

解码时有什么方法可以使用其中一个构造函数吗?

Is there any way to use either of this constructors when decoding?

• NSDecimalNumber(string: "1.66")
• NSDecimalNumber(value: 166).dividing(by: 100)
• Decimal(166)/Decimal(100)
• Decimal(sign: .plus, exponent: -2, significand: 166)

• NSDecimalNumber(string: "1.66")
• NSDecimalNumber(value: 166).dividing(by: 100)
• Decimal(166)/Decimal(100)
• Decimal(sign: .plus, exponent: -2, significand: 166)

这是我从外部服务收到的JSON的简化版本:

Here is a simplified version of the JSON I receive from the external service:

{ "priceAfterTax": 150.00, "priceBeforeTax": 130.43, "tax": 15.00, "taxAmount": 19.57 }

注意:我无法更改接收到的要解码的内容，我只能使用十进制数字.

Note: I can't change what is being received to be decoded, I'm stuck working with decimal numbers.

推荐答案

您可以实现自己的解码方法，并以最多两个小数位数的形式设置double格式，然后使用该字符串初始化您的十进制属性:

You can implement your own decoding method and format your double with maximum two fraction digits and use the string to initialize your decimal properties:

struct Root: Codable { let priceAfterTax, priceBeforeTax, tax, taxAmount: Decimal }

extension Root { public init(from decoder: Decoder) throws { var container = try decoder.container(keyedBy: CodingKeys.self) let priceAfterTaxDouble = try container.decode(Double.self, forKey: .priceAfterTax) priceAfterTax = Decimal(string: Formatter.decimal.string(for: priceAfterTaxDouble)!) ?? 0 let priceBeforeTaxDouble = try container.decode(Double.self, forKey: .priceBeforeTax) priceBeforeTax = Decimal(string: Formatter.decimal.string(for: priceBeforeTaxDouble)!) ?? 0 let taxDouble = try container.decode(Double.self, forKey: .tax) tax = Decimal(string: Formatter.decimal.string(for: taxDouble)!) ?? 0 let taxAmountDouble = try container.decode(Double.self, forKey: .taxAmount) taxAmount = Decimal(string: Formatter.decimal.string(for: taxAmountDouble)!) ?? 0 } }

extension Formatter { static let decimal: NumberFormatter = { let formatter = NumberFormatter() formatter.numberStyle = .decimal formatter.decimalSeparator = "." formatter.maximumFractionDigits = 2 return formatter }() }

let data = Data(""" { "priceAfterTax": 150.00, "priceBeforeTax": 130.43, "tax": 15.00, "taxAmount": 19.57 } """.utf8) let decodedObj = try! JSONDecoder().decode(Root.self, from: data) decodedObj.priceAfterTax // 150.00 decodedObj.priceBeforeTax // 130.43 decodedObj.tax // 15.00 decodedObj.taxAmount // 19.57