检测NSNumber是否为零，零或0 [英] Detect if NSNumber is zero, nil or 0

问题描述

我在核心数据中有一个变量.我要检测的情况是它为nil零，null或否则没有很好的值，例如222或333.

I have a variable in core data. I want to detect for the cases where it is nil zero, null or otherwise does not have a nice value such as 222 or 333.

这应该是微不足道的，但是我被Objective-C的语法所困扰.

This should be trivial but I am getting caught up in Objective-C's syntax.

以下代码不起作用:

if (_item.id!=nil && _item.id!=0) {
//do something
}

注释ID应该是一个NSNumber.

Of note id should be an NSNumber.

它定义为

@property (nonatomic, retain) NSNumber * id;

我应该澄清一下，当该值以0记录到控制台时，它不起作用.

I should clarify that it is not working when the value logs to console as 0.

考虑到变量类型和核心数据的工作方式，我无法告诉您是什么导致变量以"0"记录到控制台，但是某种原因导致了它这样做.基本上，我想排除值不是非零整数(用数学方法，而不是计算机科学术语)的情况.

Given the way variable types and core data work, I cannot tell you what causes the variable to log to console as '0' but something is causing it to do so. Basically, I want to exclude cases where the value is anything other than a non-zero integer (in mathematical, not computer science terms).

推荐答案

要检查存储在NSNumber中的数值，您必须调用一种为您提供原始类型的方法.

To check the numeric value stored in an NSNumber, you have to call one of the methods which give you a primitive type.

例如integerValue，unsignedLongLongValue，doubleValue

要正确检查nil和值0，您需要以下内容:

To correctly check for nil and a value of 0, you need the following:

if (_item.id != nil && [_item.id intValue] != 0) {
    // code here
}

由于向nil引用发送消息会返回0，因此您可以使用快捷方式:

Because sending a message to a nil reference returns 0, you can take a shortcut:

if ([_item.id intValue] != 0) ...

之所以可行，是因为_item.id必须为非零，才能从intValue返回非零值.

This works because _item.id has to be non-nil to return a non-zero value from intValue.

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