When starting a new app, it’s important to decide how it’s going to handle and display numbers. Once that has been decided, you can add some practic static NumberFormatters that encapsulate that decisions to reuse across the app.
Some examples include:
- Currency
- Decimal
- Percentage
Example code:
public extension NumberFormatter {
/// Number formatter for currencies.
/// - Parameter locale: The locale to use in the formatter. Default: `.current`.
/// - Parameter usesGroupingSeparator: Determines whether the receiver displays the group separator.
/// - Parameter minimumFractionDigits: The minimum number of fraction digits to be displayed by the number formatter. Default is `0`.
/// - Parameter maximumFractionDigits: The maximum number of fraction digits to be displayed by the number formatter. Default is `2`.
/// - Returns: The NumberFormatter with the applied properties.
static func currency(
locale: Locale = .current,
usesGroupingSeparator: Bool = true,
minimumFractionDigits: Int = 0,
maximumFractionDigits: Int = 2
) -> NumberFormatter {
let formatter = NumberFormatter()
formatter.numberStyle = .currency
formatter.locale = locale
formatter.usesGroupingSeparator = usesGroupingSeparator
formatter.minimumFractionDigits = minimumFractionDigits
formatter.maximumFractionDigits = maximumFractionDigits
return formatter
}
}
It’s important to add the Locale as one of the parameters, to be able to inject it from the outside, and therefore, making it testable for different locales:
Testing - en-US Locale
func test_currencyFormatter_en_us_locale() {
let usLocale: Locale = .init(identifier: "en-US")
let formatter: NumberFormatter = .currency(locale: usLocale)
let keyValuePairs: [Double: String] = [
0: "$0",
5.1: "$5.1",
10.10: "$10.1",
15: "$15",
1_000: "$1,000",
1_000.35: "$1,000.35",
1_000.351: "$1,000.35",
1_000.359: "$1,000.36"
]
keyValuePairs.forEach { element in
// When
let formatted = formatter.string(for: NSNumber(value: element.key))
// Then
XCTAssertEqual(formatted, element.value)
}
}
Testing - es-AR Locale
func test_currencyFormatter_es_ar_locale() {
let esLocale: Locale = .init(identifier: "es-AR")
let formatter: NumberFormatter = .currency(locale: esLocale)
let keyValuePairs: [Double: String] = [
0: "$ 0",
5.1: "$ 5,1",
10.10: "$ 10,1",
15: "$ 15",
1_000: "$ 1.000",
1_000.35: "$ 1.000,35",
1_000.351: "$ 1.000,35",
1_000.359: "$ 1.000,36"
]
keyValuePairs.forEach { element in
// When
let formatted = formatter.string(for: NSNumber(value: element.key))
// Then
XCTAssertEqual(formatted, element.value)
}
}
You can find the other formatters, plus additional tests in this repository.