Question

How can I convert between currencies in Objective-C, using either the Cocoa or Cocoa Touch frameworks?

Answer 1

Well, aren’t you a lucky fellow:

https://github.com/davedelong/DDUnitConverter

Simply copy the entire “DDUnitConverter” subfolder into your project, then do:

#import "DDUnitConverter.h"
#import "DDCurrencyUnitConverter.h"

- (void) convertCurrency {
  DDUnitConverter *converter = [DDUnitConverter currencyUnitConverter];
  NSNumber *from = [NSNumber numberWithInt:42];
  NSNumber *to = [converter convertNumber:from fromUnit:DDCurrencyUnitUKPoundSterling toUnit:DDCurrencyUnitUSDollar];
  NSLog(@"new value: %@", to);
}

That will convert £42 to USD$.

Rates are pulled from the IMF automatically, but if you really need to, you can invoke -refreshExchangeRates on your unit converter instance.

The -convertNumber:fromUnit:toUnit: call will block until the rates can be downloaded and parsed. Subsequent calls will just use the already-downloaded exchange rates.