Swift - Negative string to integer conversion not being parsed correctly

Use NumberFormatter:

let numberFormatter = NumberFormatter()
numberFormatter.numberStyle = .percent
numberFormatter.multiplier = 1
numberFormatter.maximumFractionDigits = 2
numberFormatter.positivePrefix = "+"

---

let percentageChange = Double(self.percentageChange) ?? 0
let color = percentageChange < 0 ? Color.red : Color.green

Text(numberFormatter.string(for: percentageChange)).foregroundColor(color)

Note that this will make your number formatted correctly and properly localized.

Isn't it easier to check the string for the leading minus sign

if self.percentageChange.hasPrefix("-") {
   Text(self.percentageChange + "%").foregroundColor(Color.red)
} else {
   Text("+ " + self.percentageChange + "%").foregroundColor(Color.green)
}

You just need to use the Float initializer to convert floating-point string to float and then compare.

Replace:

if((Int(self.percentageChange) ?? 0) >= 0) {

With:

if((Float(percentageChange) ?? 0) >= 0) {

The better alternative is to do this:

if !self.percentageChange.hasPrefix("-") {