NSDecimalNumber 乘法奇怪

Question

ExclusivePrice、数量都是 NSDecimalNumbers。

NSDecimalNumber *price = [exclusivePrice decimalNumberByMultiplyingBy:quantity];
NSLog(@"%@ * %@ = %@", exclusivePrice, quantity, price);

我得到的结果：

2010-04-05 00:22:29.111 TestApp[13269:207] 65 * 2 = -0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000007169919476068871316457914368

我所期望的：

2010-04-05 00:22:29.111 TestApp[13269:207] 65 * 2 = 130

谁能解释一下吗？

编辑：

完整重现：

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setNumberStyle:NSNumberFormatterDecimalStyle];
NSDecimalNumber *n2 = (NSDecimalNumber *)[formatter numberFromString:@"2"];
NSDecimalNumber *n1 = (NSDecimalNumber *)[NSDecimalNumber numberWithInt:65];
NSDecimalNumber *n3 = [n1 decimalNumberByMultiplyingBy:n2];
NSLog(@"%@ * %@ = %@", n1, n2, n3);

Answer 1

似乎对我有用。

NSDecimalNumber * n1 = [NSDecimalNumber decimalNumberWithString:@"65"];
NSDecimalNumber * n2 = [NSDecimalNumber decimalNumberWithString:@"2"];

NSDecimalNumber * res = [n1 decimalNumberByMultiplyingBy:n2];

NSLog(@"%@ * %@ = %@", n1, n2, res);

输出：

2010-04-05 08:40:42.812 x[24301] 65 * 2 = 130

Answer 2

我找到了答案：根据 How to use NSDecimalNumber? 我无法轻松在 NSNumber 和 NSDecimalNumber 之间转换。要从一种转换为另一种，我必须这样做：

NSDecimalNumber *n2 = [NSDecimalNumber decimalNumberWithDecimal:
                              [[formatter numberFromString:@"2"] decimalValue]];

如果 NSNumberFormatter 有一个decimalNumberFromString: 方法，那就太好了。