(null)与< null>有什么区别? [英] What's the difference between (null) vs <null>?
问题描述
在我将其范围缩小到特定方法之前，我的应用程序中出现随机崩溃.在该方法中，我希望使用 NSString 作为参数.该 NSString 有时可以为nil，在这种情况下，该方法将终止并且不会造成任何危害.
I was getting random crashes in my app until I narrowed it down to a particular method. In that method I expect an NSString as a parameter. This NSString can sometimes be nil in which case the method ends and no harm is done.
当我通过 NSLog(@％@"，myString)运行方法的参数时，我发现其中之一:
When I run my method's parameter through NSLog(@"%@", myString) I found that I get one of these:
- 实际NSString的内容
- (空)
- < null>
前两个是我的方法所期望和处理的.第三个< null> 使-[NSNull length]:无法识别的选择器发送到实例0x1b2ace8 导致我的应用程序崩溃.
The first two are expected and handled by my method. The third one, <null>, crashes my app with -[NSNull length]: unrecognized selector sent to instance 0x1b2ace8.
我已经通过检查 nil 或 isKindOfClass 找到了解决该问题的方法，但是我的问题是(空)和<之间有什么区别?null>?.
I have found a way around the problem by checking for nil or isKindOfClass, but my question is what is the difference between (null) and <null>?.
推荐答案
(null)是使用格式说明符 nil .< null> 是向 NSNull 单例(您通过 [NSNull null] description 的结果>).
(null) is the string that NSLog() prints when you use the format specifier %@ with a nil value. <null> is the result of sending description to the NSNull singleton (which you access via [NSNull null]).
NSNull 在可可集合( NSArray 和 NSDictionary )中用作无对象"占位符，因为它们不能包含 nil.
NSNull is used as a "no object" placeholder in Cocoa collections (NSArray and NSDictionary) because they cannot contain nil.
这两个描述字符串令人困惑，它们相似，并且可能会争辩说 NSNull 应该针对它提一个错误，以使其更加清楚.
The two description strings are confusingly similar, and one could argue that NSNull should have a bug filed against it to make this a little more clear.
这篇关于(null)与< null>有什么区别?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
