kCFNull 和 [NSNull null] 可以互换吗
它似乎
if(myObj == (typeOfMyObj *) kCFNull){
//myObj is null
}
并
if(myObj == (typeOfMyObj *) [NSNull null]){
//myObj is null
}
产生相同的结果。
情况总是如此吗？我正在开发一个 iOS 5 应用程序。
谢谢！
It seems to be
if(myObj == (typeOfMyObj *) kCFNull){
//myObj is null
}
and
if(myObj == (typeOfMyObj *) [NSNull null]){
//myObj is null
}
produce the same result.
Is this always the case? I'm developing an iOS 5 application.
Thanks!
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评论（2）
似乎 Apple 的文档都没有声明
NSNull和CFNullRef是免费桥接的，但似乎它们自CFNullRef以来一直都是免费桥接的> 在 Mac OS X 10.2 中引入。NSNull从 Mac OS X 10.0 开始可用。最后，它们实际上都只是充当杰出 NULL 对象的哨兵值。可能有一种方法可以让您的代码避免依赖
kCFNull == [NSNull null]，但如果您由于某种原因不能这样做，那么我不会太担心。It appears none of Apple's docs state that
NSNullandCFNullRefare toll-free-bridged, but it nevertheless seems that they are and have been sinceCFNullRefwas introduced in Mac OS X 10.2.NSNullwas available starting with Mac OS X 10.0. In the end, they are both really just sentinel values that serve as a distinguished NULL object.There's probably a way for your code to avoid depending on
kCFNull == [NSNull null], but if you can't for some reason, then I wouldn't worry about it too much.我同意 Jeremy 的观点，
如果你想 100% 安全，最好的选择是使用 isKindOfClass 检查类：
即：
或者
然后你就可以安全地应对未来的任何更改，尽管它非常乏味并且是所有建议方法中最慢的:P
是这样的问题也不是不可能的
有一天，甚至
，尽管
这些问题导致大多数 Obj-C 开发者花更多的时间在各种麻烦上而不是编写代码 :P
I agree with Jeremy,
If you wanted to be 100% safe, the best bet would be to check the class using isKindOfClass:
ie:
or
Then you're safe against any future changes, though it's super tedious and the slowest of all proposed approaches :P
It's not out of the question that one day
but
or even
Though these are the sorts of concerns that cause most Obj-C devs to spend more time jumping through hoops than writing code :P