使用 Swift 将 JSON 字符串转换为数字时出错

Question

我有一个基本问题是在 Swift 中将字符串转换为数字。我发现了一个很好的堆栈溢出 question，它可以帮助我将 JSON 字符串转换为数字，但是 当我尝试添加或减去这些值时出现错误。

我确定我遗漏了一些明显的东西！

菲尔

错误：在“BinaryInteger”上引用运算符函数“-”要求“NSNumber”符合“BinaryInteger”

func red2G()->String {
        let numberFormatter = NumberFormatter()
        
        // Prev Close
        let number1  = numberFormatter.number(from: pricesAlpha?.globalQuote.prevClose ?? "0.000")
        if let final1 = number1?.floatValue {
        print("Returned number is " + String(format: "%.2f", final1))
        }
        
        // Open
        let number2  = numberFormatter.number(from: pricesAlpha?.globalQuote.open ?? "0.000")
        if let final2 = number2?.floatValue {
        print("Returned number is " + String(format: "%.2f", final2))
        }
        
        // Price
        let number3  = numberFormatter.number(from: pricesAlpha?.globalQuote.price ?? "0.000")
        if let final3 = number3?.floatValue {
        print("Returned number is " + String(format: "%.2f", final3))
        }
        
        return String(number3-number2)
     }

我根据建议的答案简化了函数：

    func load(symbolName:String) {
        self.symbolName = symbolName
    }
    
    func red2G()->String {
        let numberFormatter = NumberFormatter()
        
        // Prev Close
        let prevClose  = numberFormatter.number(from: pricesAlpha?.globalQuote.prevClose ?? "0.000")?.floatValue
        
        // Open
        let openPrice  = numberFormatter.number(from: pricesAlpha?.globalQuote.open ?? "0.000")?.floatValue
        
        // Price
        let currentPrice  = numberFormatter.number(from: pricesAlpha?.globalQuote.price ?? "0.000")?.floatValue
        
        return String((openPrice ?? 0.00) - (prevClose ?? 0.00) - (currentPrice ?? 0.00))
}

值基于此 JSON 字典

struct GlobalQuote: Codable {
    let globalQuote: PriceAlpha
    
    enum CodingKeys : String, CodingKey {
        case globalQuote = "Global Quote"
    }
}

struct PriceAlpha: Codable {
    let symbol: String
    let open: String
    let high: String
    let low: String
    let price: String
    let volume: String
    let tradingDay: String
    let prevClose: String
    let change: String
    let pctChange: String
    
    enum CodingKeys : String, CodingKey {
        case symbol = "01. symbol"
        case open = "02. open"
        case high = "03. high"
        case low = "04. low"
        case price = "05. price"
        case volume = "06. volume"
        case tradingDay = "07. latest trading day"
        case prevClose = "08. previous close"
        case change = "09. change"
        case pctChange = "10. change percent"
    }
}

Answer 1

NSNumber 是一个围绕实际整数或浮点数等的对象包装器。您在代码中看到您调用floatValue 的位置？这得到了一个实际的数字，你可以用它来做数学运算。将final3 和final2 保留在他们的if 语句之外，然后计算一下。

也就是说，您几乎肯定应该在PriceAlpha 中实现自定义解码和编码，以便结构已经包含正确语义类型的值（例如Float）而不是String。但是对于财务信息，您实际上需要Decimal，而不是Float。