在swift中无法将两个字符串值相乘

Question

我从JSON中获得字符串格式的浮点值，如下

JSON:

{
"result": {
"conversion_factor": {
"conv_factor": "0.820000"
}
"search_result": [
{
"service_details": [
{
"standard_rate_in_usd": "10.00",

现在我需要乘以conv_factor * standard_rate_in_usd

代码:这段代码只有第一个值是正确的，剩下的显示错误，为什么?

let indexData = searchResult?.result?.search_result?[indexPath.row]
if let servDetls = indexData?.service_details{
for oneSerdet in servDetls{

var stringPrice: String?

if var priceVal = Float(oneSerdet.standard_rate_in_usd!), var convVal = Float((searchResult?.result?.conversion_factor?.conv_factor)!) {
stringPrice = String(priceVal * convVal)
}
else{
stringPrice = ""
}
cell.priceLbl.text = "£ (stringPrice ?? "") (currData)"
}
}

Answer 1

需要转换为浮点数:

let convResult = Float(oneSerdet.standard_rate_in_usd) * 
Float(searchResult?.result?.conversion_factor?.conv_factor)

Answer 2

尝试一下，希望这将解决您的问题

if let conv_factor = oneSerdet.conv_factor,
let factor = Double(conv_factor),
let standard_rate_in_usd = oneSerdet.standard_rate_in_usd,
let usd = Double(standard_rate_in_usd) {
print(factor*usd)
cell.priceLbl.text = "(factor*usd)"
}else{
cell.priceLbl.text = ""
print("Unreachable")
}

Answer 3

你有很多问题:

1. 您的结构searchResult?.result?.conversion_factor?.conv_factor计算为可选字符串:String?.

2. 字符串不能相乘。字符串不是数字。您需要将字符串转换为Double类型。但是接受字符串的Double初始化式也返回一个Optional类型(因为"Apple"不能转换为Double类型)。

下面是一些示例代码，将接受2个可选字符串，尝试将它们转换为double，并将它们相乘。

let xString: String? = "123.456"
let yString: String? = "2.0"
let x = xString.map { Double($0) ?? 0 } ?? 0.0
let y = yString.map { Double($0) ?? 0 } ?? 0.0
let result: Double = x * y
print(result)

输出

246.912