Objective-C字典是有序容器吗？ [英] Is the Objective-C dictionary an ordered container?

问题描述

作为标题，当我将元素插入到目标c中的字典中（顺序如下：k1，k2，k3），是否有任何保证，当我枚举如下：

  for（k in dictionary）{
 //输出k值
} 
  / pre> 
 
 
它会以相同的顺序显示？
解决方案
不， NSDictionary 不保留其键的插入顺序。
 
 
 
如果您需要一个维护插入顺序的字典我建议使用 CHDataStructures框架，它有一个 CHOrderedDictionary  class（它是 NSMutableDictionary 的后代）。  CHOrderedDictionary 的文档说：
 
 
列出顺序中的键的字典它们被插入。
 
 
 
提供以下附加操作以利用以下顺序：
 
 
 
 -firstKey 
 
 
 
 -lastKey 
 
 
 
 -keyAtIndex：
 
 
 
 -reverseKeyEnumerator 
 
 
 
键值条目插入正常字典中，包括替换现有键的值，如-setObject：forKey：所详述。但是，并行使用一个额外的结构来跟踪插入顺序，并按顺序枚举密钥。如果要添加的密钥目前不存在于字典中，则将其添加到列表的末尾，否则键的插入顺序不会更改。
 
 
 
as the title, when I insert element to a dictionary in objective-c (in order like: k1, k2, k3), is there any guarantee that when I enumerate it like:
for ( k in dictionary ){
   // output the k - value
}
it would show in the same order?
解决方案
No, NSDictionary does not maintain the insertion order of its keys.

If you need a dictionary that maintains insertion order, I'd suggest using the CHDataStructures framework, which has a CHOrderedDictionary class (it's a descendent of NSMutableDictionary).  The documentation for CHOrderedDictionary says:

  
A dictionary which enumerates keys in the order in which they are inserted.
  
  
The following additional operations are provided to take advantage of the ordering:
  
  
-firstKey
  
  
-lastKey
  
  
-keyAtIndex:
  
  
-reverseKeyEnumerator
  
  
Key-value entries are inserted just as in a normal dictionary, including replacement of values for existing keys, as detailed in -setObject:forKey:. However, an additional structure is used in parallel to track insertion order, and keys are enumerated in that order. If a key to be added does not currently exist in the dictionary, it is added to the end of the list, otherwise the insertion order of the key does not change.


                        
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