Format currency in a UITextField

I did a little different. That way I have the number entered by the user formatted in UITextField (valueTextField.text) and I have a version of it with only numbers (storeValue) in case I need to do accounts and these things.

In @interface :

   NSMutableString *storeValue;
   NSNumberFormatter *numberFormatter; 

In viewDidLoad: :

    storeValue = [NSMutableString new];
    numberFormatter = [NSNumberFormatter new];
    [numberFormatter setNumberStyle:NSNumberFormatterCurrencyStyle];
    [super viewDidLoad];

And in shouldChangeCharactersInRange:

    if (textField == valueTextField) {
        if (string.length == 0) {
            int length = (storeValue.length - 1);
            if (length >= 0) {
                NSRange range = NSMakeRange(length, 1);
                [storeValue deleteCharactersInRange:range];
            };
        } else if ([textField.text length] <= 7) {
            [storeValue appendString:string];
        }

        NSString *newText = [numberFormatter stringFromNumber:[NSNumber numberWithFloat:([storeValue doubleValue] / 100)] ];
        [textField setText:[NSString stringWithFormat:@"%@",newText]];

        return NO;
    }

    return YES;

David, there are simpler ways to solve this problem. Try changing the style of the number to NSNumberFormatterCurrencyStyle and putting a location as a reference for the formatting.

NSNumberFormatter *n = [[NSNumberFormatter alloc] init];
[n setNumberStyle:NSNumberFormatterCurrencyStyle];
NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"pt_BR"];
[n setLocale:locale];
NSString *saída = [n stringFromNumber:[NSNumber numberWithFloat:125.98]];

The output will be $ 125.98.

I have something a little different in shouldChangeCharactersInRange in an application of mine working the way you want it.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    if ([textField tag] == 1) { // Só para identificar o campo de moeda
        NSString *replaced = [textField.text stringByReplacingCharactersInRange:range withString:string];
        NSDecimalNumber *amount = (NSDecimalNumber*) [self.formatter numberFromString:replaced];
        if (amount == nil) {
            return NO;
        }
        short powerOf10 = 0;
        if ([textField.text isEqualToString:@""]) {
            powerOf10 = -self.formatter.maximumFractionDigits;
        } else if (range.location + self.formatter.maximumFractionDigits >= textField.text.length) {
            if (range.length) {
                powerOf10 = -range.length;
            } else {
                powerOf10 = [string length];
            }
        }
        amount = [amount decimalNumberByMultiplyingByPowerOf10:powerOf10];
        textField.text = [self.formatter stringFromNumber:amount];
        return NO;
    }

    return YES;
}

And in viewDidLoad: I have my property formatter used above:

self.formatter = [NSNumberFormatter new];
[self.formatter setNumberStyle:NSNumberFormatterCurrencyStyle];
[self.formatter setLenient:YES];
[self.formatter setGeneratesDecimalNumbers:YES];
[self.formatter setCurrencySymbol:@""];
[self.formatter setInternationalCurrencySymbol:@""];

locale is not required, as it is already set in device settings unless you want something different.

David Batista's response was very helpful.

I'm writing the code in Swift and it worked very well.

if ((string as NSString).length == 0) {
        var length = (storeValue.length - 1);
        if (length >= 0) {
            var range = NSMakeRange(length, 1)

            storeValue.deleteCharactersInRange(range)
        }
    } else if ( (textField.text as NSString).length <= 15) {
        storeValue.appendString(string)
    }

    var newText = numberFormatter.stringFromNumber(NSNumber(double: storeValue.doubleValue/100))
    textField.text = NSString(format: "%@", newText!) as String

    return false