将PayPal-iOS-SDK pod与RubyMotion集成

Question

我正在将PayPal-iOS-SDK pod与RubyMotion集成，但是在运行这行代码时应用程序崩溃了：

subtotal = PayPalItem.totalPriceForItems(items)

我正在尝试将此Objective-C代码移植到RubyMotion

    PayPalItem *item1 = [PayPalItem itemWithName:@"Blue Jeans"

                                  withQuantity:2

                                     withPrice:[NSDecimalNumber decimalNumberWithString:@"34.89"]

                                  withCurrency:@"USD"

                                       withSku:@"Hip-00010"];

  PayPalItem *item2 = [PayPalItem itemWithName:@"Red Jeans"

                                  withQuantity:1

                                     withPrice:[NSDecimalNumber decimalNumberWithString:@"0.00"]

                                  withCurrency:@"USD"

                                       withSku:@"Hip-00020"];

  PayPalItem *item3 = [PayPalItem itemWithName:@"Black Jeans"

                                  withQuantity:1

                                     withPrice:[NSDecimalNumber decimalNumberWithString:@"29.99"]

                                  withCurrency:@"USD"

                                       withSku:@"Hip-00030"];

  NSArray *items = @[item1, item2, item3];

  NSDecimalNumber *subtotal = [PayPalItem totalPriceForItems:items];

这是我的RubyMotion代码：

item1 = PayPalItem.itemWithName('Blue Jeans',
                   withQuantity: 2,
                   withPrice: NSDecimalNumber.decimalNumberWithString('34.89'),
                   withCurrency: 'USD',
                   withSku: 'Hip-00010')

item2 = PayPalItem.itemWithName('Red Jeans',
                   withQuantity: 1,
                   withPrice: NSDecimalNumber.decimalNumberWithString('0.00'),
                   withCurrency: 'USD',
                   withSku: 'Hip-00020')

item3 = PayPalItem.itemWithName('Black Jeans',
                   withQuantity: 1,
                   withPrice: NSDecimalNumber.decimalNumberWithString('29.99'),
                   withCurrency: 'USD',
                   withSku: 'Hip-00030')

items = [item1, item2, item3]

subtotal = PayPalItem.totalPriceForItems(items)

但是，当应用程序到达此行时，应用程序崩溃了：

subtotal = PayPalItem.totalPriceForItems(items)

这是我得到的错误：

2014-05-08 19：26：56.492 B4TS [8230：70b] - [__ NSCFNumber decimalNumberByMultiplyingBy：]：无法识别的选择器发送到实例0xcae0550 2014-05-08 19：26：57.808 B4TS [8230：70b] * 由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因：' - [__ NSCFNumber decimalNumberByMultiplyingBy：]：无法识别的选择器发送到实例0xcae0550 “

非常感谢任何帮助。