麻烦与NSDecimalNumber的decimalNumberByDividingBy：withBehavior： [英] Trouble with NSDecimalNumber's decimalNumberByDividingBy:withBehavior:

问题描述

我总是似乎遇到麻烦NSDecimalNumber！今天，我收到此错误：

I always seem to run into trouble with NSDecimalNumber! Today, I get this error:

由于未捕获异常而终止应用程序'NSInvalidArgumentException' ** - [NSCFNumber decimalNumberByDividingBy：withBehavior：]：无法识别的选择器发送到实例0xd1fb10

是错误的根源：

- (void)setUpInstance {
    static NSDecimalNumberHandler* roundingBehavior = nil;
    if (roundingBehavior == nil) {
        roundingBehavior = [[NSDecimalNumberHandler alloc] initWithRoundingMode:NSRoundDown scale:2 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:NO];
    }   
    NSDecimalNumber *amount = viewController.aDecimalNumber;
    NSDecimalNumber *actualValue = viewController.anotherDecimalNumber;
    integralPortion = [amount decimalNumberByDividingBy:actualValue withBehavior:roundingBehavior];
    ...
}

文档将方法定义为：

-(NSDecimalNumber*)decimalNumberByDividingBy:(NSDecimalNumber *)decimalNumber
                                withBehavior:(id<NSDecimalNumberBehaviors>)behavior

我不能解释（id< NSDecimalNumberBehaviors>）行为参数。这不是只是ANY对象，只要它符合NSDecimalNumbersBehaviors协议？

I must not be interpreting the "(id<NSDecimalNumberBehaviors>)behavior" argument correctly. Isn't that just ANY object as long as it conforms to the NSDecimalNumbersBehaviors protocol?

我做错了什么？

星期五快乐！

推荐答案

今天，我得到这个错误：终止应用程序由于未捕获异常'NSInvalidArgumentException'，原因：'*** - [NSCFNumber decimalNumberByDividingBy：withBehavior：]：无法识别的选择器发送到实例0xd1fb10'

Today, I get this error: "Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSCFNumber decimalNumberByDividingBy:withBehavior:]: unrecognized selector sent to instance 0xd1fb10'"

这意味着你发送消息到一个纯NSNumber（NSCFNumber幕后）。您只能将其发送到NSDecimalNumber。

That means you're sending that message to a plain NSNumber (NSCFNumber behind the scenes). You can only send it to an NSDecimalNumber.

请注意，如何声明变量是不相关的。你可以声明 amount 为 NSString * amount ，你会得到完全相同的异常，包括NSCFNumber作为类名，因为它是一个异常，它发生在运行时。 （您当然也会收到关于NSString和NSDecimalNumber不可互换的编译时警告。）

Note that how you declare the variables is irrelevant. You could declare amount as NSString *amount and you would get the exact same exception, including NSCFNumber as the class name, because it is an exception, which happens at run-time. (You would, of course, also get the compile-time warning about NSString and NSDecimalNumber not being interchangeable.)

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