NSDecimalNumber增殖奇异性

Question

我见过一个关于这个的similar topic，但是这似乎是因为等式在某个地方使用了NSNumber。我已经检查了我的所有代码，我所能看到的就是我正在使用NSDecimalNumbers作为我的方程。

我得到了一个JSON got服务，它返回一些定价号。

在对象属性中解析它们之后，我想用它们运行以下等式：

NetPrice *(1+ (RawPercentage / 100)) + FixedPrice = processedNetPrice

更新:我将代码更改为：

    NSDecimalNumber *one = [NSDecimalNumber one];

    if (!self.netPrice || [self.netPrice isKindOfClass:[NSNull class]]) 
    { self.netPrice = [NSDecimalNumber zero]; }

    NSDecimalNumber *nettoPrijs = self.netPrice;
    NSLog(@"self.netPrice = %@",self.netPrice);
    //Returns: self.netPrice = 89.25

    NSLog(@"nettoPrijs = %@",nettoPrijs);
    //Returns: nettoPrijs = 89.25

    if (!self.userData.BandFixed || [self.userData.BandFixed isKindOfClass:[NSNull class]]) 
    { self.userData.BandFixed = [NSDecimalNumber zero]; }

    NSDecimalNumber *fixedPrice = self.userData.BandFixed;

    NSLog(@"self.userData.BandFixed = %@",self.userData.BandFixed);
    //Returns: self.userData.BandFixed = 0

    NSLog(@"fixedPrice = %@",fixedPrice);
    //Returns: fixedPrice = 0

    if (!self.userData.BandPercentage || [self.userData.BandPercentage isKindOfClass:[NSNull class]]) 
    { self.userData.BandPercentage = [NSDecimalNumber zero]; }

    NSDecimalNumber *rawPercentage = self.userData.BandPercentage;

    NSLog(@"self.userData.BandPercentage = %@",self.userData.BandPercentage);
    //Returns: self.userData.BandPercentage = 0

    NSLog(@"rawPercentage = %@",rawPercentage);
    //Returns: rawPercentage = 0

    NSDecimalNumber *percentage = [rawPercentage decimalNumberByMultiplyingByPowerOf10:-2];
    NSLog(@"percentage = %@",percentage);
    //Returns: percentage = 0

    NSDecimalNumber *onePercent = [one decimalNumberByAdding:percentage];
    NSLog(@"onePercent = %@",onePercent);
    //Returns: onePercent = 1

    NSDecimalNumber *onePercentTimesNetPrice = [onePercent decimalNumberByMultiplyingBy:nettoPrijs];
    NSLog(@"onePercentTimesNetPrice = %@",onePercentTimesNetPrice);
    //Returns: onePercentTimesNetPrice =        
    -0.000000000000000000000000000000000000000000000000000000000000000000000
    00000000000000000000000000359498933794611654993903616

    NSDecimalNumber *addingFixed = [onePercentTimesNetPrice decimalNumberByAdding:fixedPrice];
    NSLog(@"addingFixed = %@",addingFixed);
    //Returns: addingFixed =  
    -0.000000000000000000000000000000000000000000000000000000000000000000000
    00000000000000000000000000359498933794611654993903616

如果我改变了：

NSDecimalNumber *onePercentTimesNetPrice = [onePercent decimalNumberByMultiplyingBy:nettoPrijs];

至：

NSDecimalNumber *onePercentTimesNetPrice = [nettoPrijs decimalNumberByMultiplyingBy:onePercent];

它崩溃了：

-[__NSCFNumber decimalNumberByMultiplyingBy:]: unrecognized selector sent to instance 0x84ad160

Answer 1

正如您的NSLog()输出所示，self.userData.RawPercentage和self.userData.FixedPrice是nil，即没有将+初始化为NSDecimalNumber对象。

nil不能用来表示十进制数0！

事实上，当我尝试你的代码时，

NSDecimalNumber *custPrice1 = [oneWithNet decimalNumberByAdding:priceFixed];

因为priceFixed为零而崩溃。

因此，您应该检查这些变量初始化的代码，并确保它们指向有效的NSDecimalNumber对象。

更新：错误消息

-[__NSCFNumber decimalNumberByMultiplyingBy:]: unrecognized selector sent to instance 0x84ad160

显示nettoPrijs是NSNumber对象，而不是NSDecimalNumber。下面的简化代码显示了如果您试图将NSDecimalNumber与NSNumber相乘会发生什么

NSDecimalNumber *one = [NSDecimalNumber one];
id price = [NSNumber numberWithFloat:89.25];
NSDecimalNumber *product = [one decimalNumberByMultiplyingBy:price];
NSLog(@"product = %@", product);
// Output:
// product = -0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000221166721562906606351581184

(我不知道为什么这不会崩溃或产生一些错误消息。)如果您与NSDecimalNumber相乘，它将正确工作。

price = [NSDecimalNumber decimalNumberWithString:@"89.25"];
product = [one decimalNumberByMultiplyingBy:price];
NSLog(@"product = %@", product);
// Output:
// product = 89.25

因此，我假设self.netPrice是一个必须转换为NSDecimalNumber的NSNumber对象。同样的情况也适用于其他数字对象。

Answer 2

我用以下方法修复了它：

- (void) doMath
{
    NSDecimalNumber *one = [NSDecimalNumber one];
    NSLog(@"Band: %@ one = %@",self,one);
    if (!self.netPrice || [self.netPrice isKindOfClass:[NSNull class]]) { self.netPrice = [NSDecimalNumber zero]; }
    NSDecimalNumber *nettoPrijs = self.netPrice;
    NSLog(@"self.netPrice = %@",self.netPrice);
    NSLog(@"nettoPrijs = %@",nettoPrijs);
    if (!self.userData.BandFixed || [self.userData.BandFixed isKindOfClass:[NSNull class]]) { self.userData.BandFixed = [NSDecimalNumber zero]; }
    NSDecimalNumber *fixedPrice = self.userData.BandFixed;
    NSLog(@"self.userData.BandFixed = %@",self.userData.BandFixed);
    NSLog(@"fixedPrice = %@",fixedPrice);
    if (!self.userData.BandPercentage || [self.userData.BandPercentage isKindOfClass:[NSNull class]]) { self.userData.BandPercentage = [NSDecimalNumber zero]; }
    NSDecimalNumber *rawPercentage = self.userData.BandPercentage;
    NSLog(@"self.userData.BandPercentage = %@",self.userData.BandPercentage);
    NSLog(@"RawPercentage = %@",rawPercentage);
    NSDecimalNumber *percentage = [rawPercentage decimalNumberByMultiplyingByPowerOf10:-2];
    NSLog(@"percentage = %@",percentage);
    NSDecimalNumber *onePercent = [one decimalNumberByAdding:percentage];
    NSLog(@"onePercent = %@",onePercent);

NSDecimalNumber gertje = NSDecimalNumber decimalNumberWithDecimal:nettoPrijs.decimalValue；* NSDecimalNumber *onePercentTimesNetPrice = gertje decimalNumberByMultiplyingBy:onePercent;

    NSLog(@"onePercentTimesNetPrice = %@",onePercentTimesNetPrice);
    NSDecimalNumber *addingFixed = [onePercentTimesNetPrice decimalNumberByAdding:fixedPrice];
    NSLog(@"addingFixed = %@",addingFixed);
}

谢谢你的帮助！