当键不存在时，NSMutableDictionary 返回 0xffffffff 而不是 nil
我有一个 NSMutableDictionary 正在做一些奇怪的事情：
(gdb) po listenerRegistry
{
}
(gdb) po productID
com.mycompany.productid
(gdb) po [listenerRegistry objectForKey:[productID stringValue]]
0xffffffff does not appear to point to a valid object.
(gdb) po [listenerRegistry class]
__NSCFDictionary
(gdb)
根据文档，对于不在字典中的键，应该返回 nil 。
以前有其他人见过这个吗？
I have an NSMutableDictionary that is doing something strange:
(gdb) po listenerRegistry
{
}
(gdb) po productID
com.mycompany.productid
(gdb) po [listenerRegistry objectForKey:[productID stringValue]]
0xffffffff does not appear to point to a valid object.
(gdb) po [listenerRegistry class]
__NSCFDictionary
(gdb)
According to the docs, nil is supposed to be returned for keys that aren't in the dictionary.
Has anyone else seen this before?
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回答我自己的问题。
NSMutableDictionary中的对象属于id类型，并且 Monolo 的观察结果似乎是正确的，返回值看起来像NSNotFound。显然，当要求该类型的项目不存在或未找到时，基础类会返回
NSNotFound（如所讨论的 此处）。虽然文档明确列出了 NSArray，但我不得不相信我的情况也发生了同样的情况。Answering my own question.
The objects inside the
NSMutableDictionaryare of the typeid <MyObserverProtocol>, and it would appear that Monolo was right in his observation that the returned value looks likeNSNotFound.Apparently, Foundation classes return
NSNotFoundwhen asked for items of that type when they don't exist or aren't found (as discussed here). While the documentation listsNSArrays explicitly, I feel compelled to believe the same is happening in my case.