Currency conversion in Objective-C

How can I convert between currencies in Objective-C, using either the Cocoa or Coc开发者_JS百科oa Touch frameworks?

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.

Actually I've choose:

https://github.com/davedelong/DDUnitConverter

Rates are pulled from the IMF but during the conversion , there are problems using NSDecimalNumber functions ( decimalNumberByMultiplyingBy and decimalNumberByDividingBy: they dont give the correct results if you dont use NSDecimalNumber var's created by strings), so I've correct the conversion method like this and now it work:

DDUnitConverter.m

- (NSNumber *)convertNumber:(NSNumber *)number fromUnit:(DDUnit)fromUnit toUnit:(DDUnit)toUnit {
    if (fromUnit == toUnit) { return number; }

    //make sure it's an NSDecimalNumber
    NSDecimalNumber *source = [NSDecimalNumber decimalNumberWithDecimal:[number decimalValue]];

    NSDecimalNumber *convertToBaseUnit = [[self class] multiplierForUnit:fromUnit];

    NSDecimalNumber * n1 = [NSDecimalNumber decimalNumberWithString:[source stringValue]];
    NSDecimalNumber * n2 = [NSDecimalNumber decimalNumberWithString:[convertToBaseUnit stringValue]];

    NSDecimalNumber *valueInBaseUnit = [n1 decimalNumberByMultiplyingBy:n2];

    NSDecimalNumber *convertFromBaseUnit = [[self class] multiplierForUnit:toUnit];
    if ([convertFromBaseUnit isEqual:[NSDecimalNumber zero]]) {
        convertFromBaseUnit = [NSDecimalNumber one];
    }
    NSDecimalNumber * n3 = [NSDecimalNumber decimalNumberWithString:[valueInBaseUnit stringValue]];
    NSDecimalNumber * n4 = [NSDecimalNumber decimalNumberWithString:[convertFromBaseUnit stringValue]];

    NSDecimalNumber *valueInTargetUnit = [n3 decimalNumberByDividingBy:n4];

    return valueInTargetUnit;
}

One alternative, is to use the YQL (Yahoo Query Language) to retrieve the latest rates. Yahoo's dev site makes it pretty easy to get started in Objective-C and there are plenty of SO examples on YQL. http://developer.yahoo.com/social/sdk/objectivec/

You may find Yahoo is very nice and liberal with their terms & conditions for many of their data APIs. It's also a lot less fragile than a non dedicated API like Dave is using. Dave writes great code, but the IMF TSV file is not nearly as guaranteed to be available as the YQL services.