iOS: How to properly display prices and format currencies

Let's say you want to display to user that something cost 50 dollars. You might want to do something like this:

let price = 50
print("\(price) $")

Please, never ever do stuff like this 🛑

This is very naive solution that will easily confuse users and does not scale well. Because in some countries dollar sign or other currency signs are put in front of the price. Sometimes there might not be a space. With bigger sums or fractions some locales may use . while others use , or even combination of the two.

The solution is also not to remember all these rules or give up. The solution is called NumberFormatter class.

All you have to do is to use it and be mindful of small number of configuration options. Everything else is taken care of by the system.

Basic usage

The very basic usage looks like this:

let formatter = NumberFormatter()
formatter.numberStyle = .currency

You create instance of the formatter and set its style to .currency.
And then use string method to get formatted string as a currency. The drawback here is that you have to use NSNumber which can be created from Int or Double and the return type is optional string.

In practice I don't think the string will ever by nil when this method is called with valid NSNumber instance but to be sure I am often using it like this:

print(formatter.string(from: NSNumber(value: 548.5)) ?? "n/a")

Better way would be to create centralized util class to handle formatting and internally check that result of the string(from: NSNumber) is not nil and if for some reason is nil crash you app with assert during debug to get a chance to investigate the issue further.

Customizing currency

The above formatter will use user's current Locale to select currency symbol and style for the price. This may be what you want but if your app is designed to work in multiple countries and is getting data from a server, then you should set the currency manually for formatter to be sure that if your server sends price of 20 Eur for example the user will see 20 € and not something like 20 zł because they are from Poland..

You can set currency like this:

formatter.currencyCode = "EUR"
formatter.currencyCode = "USD"
// and so on..

NumberFormatter also allows you to specify locale which can be useful during testing to preview how the numbers are going to look like for people on other countries. In practice you shouldn't set this unless you have very important reason for doing so.

formatter.locale = Locale(identifier: "de-DE") // lets check how will prices look for people from Germany

Configuring fractions

If you don't want to show prices with fractional part. Meaning you want to show 10 and not 10,12. You can set the property maximumFractionDigits to specify the maximum number of fraction digits. Set it to 0 to show none 🙂

Thanks for reading!