iPhone：如何將貨幣符號的字符串轉換爲負數？

Question

說我有一個字符串是23.56英鎊或23.56美元，我怎麼能把它轉換成-23.56？

我有這部分

NSMutableString *strAmount = [NSMutableString stringWithString:txtAmount.text]; 
[strAmount replaceCharactersInRange: [strAmount rangeOfString: strCurrencySymbol] withString:@""]; 

Answer 1

這看起來像一個良好的開端。儘管創建了一組貨幣符號後，您可以使用rangeOfCharacterFromSet:而不是rangeOfString:。您的代碼看起來是這樣的：

NSMutableString *strAmount = [NSMutableString stringWithString:txtAmount.text]; 
NSCharacterSet *currencySet = [NSCharacterSet characterSetWithCharactersInString:@"$€£"]; 
[strAmount replaceCharactersInRange: [strAmount rangeOfCharacterFromSet:currencySet] withString:@"-"]; 

Answer 2

使用NSNumberFormatter

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init]; 
[formatter setNumberStyle:NSNumberFormatterCurrencyStyle]; 
[formatter setLenient:YES]; 

NSNumber *number = [formatter numberFromString:@"£23.56"]; 

NSDecimalNumber *minusOne = [NSDecimalNumber decimalNumberWithString:@"-1.00"]; 
NSDecimalNumber *money = [NSDecimalNumber decimalNumberWithDecimal:[number decimalValue]]; 
NSDecimalNumber *negativeMoney = [money decimalNumberByMultiplyingBy:minusOne]; 

NSLog(@"£23.56 is now %@", [negativeMoney description]);