ios 寻找一种优雅的方式来检查字典中是否存在密钥
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Looking for an elgant way to check if a Key exsists in a dictionary
提问by trojanfoe
Possible Duplicate:
How to check if an NSDictionary or NSMutableDictionary contains a key?
I can get the an array of the Keys (strings) from the dictionary then loop through it doing a string compare with the Key i want to check for and see if that dictionary contains the key I seek.
我可以从字典中获取键（字符串）数组，然后循环遍历它，将字符串与我要检查的键进行比较，看看该字典是否包含我要查找的键。
But is there a more elegant want to check if the key exists in the dictionary?
但是有没有更优雅的方式想要检查字典中是否存在键？
NSArray * keys = [taglistDict allKeys];
for (NSString *key in keys)
{
// do string compare etc
}
-Code
-代码
回答by trojanfoe
An NSDictionarycannot contain nilvalues, so you can simply use [NSDictionary objectForKey:]which will return nilif the key does not exist:
AnNSDictionary不能包含nil值，因此您可以简单地使用[NSDictionary objectForKey:]which 将nil在键不存在时返回：
BOOL exists = [taglistDict objectForKey:key] != nil;
EDIT: As mentioned by @OMGPOP, this also works using Objective-C literals using the following syntax:
编辑：正如@OMGPOP 所提到的，这也适用于使用以下语法的 Objective-C 文字：
NSDictionary *dict = @{ @"key1" : @"value1", @"key2" : @"value2" };
if (dict[@"key3"])
NSLog(@"Exists");
else
NSLog(@"Does not exist");
Prints:
印刷：
Does not exist
回答by Eric
Trojanfoe is likely better, but you could also do:
Trojanfoe 可能更好，但您也可以这样做：
[[taglistDict allKeys]containsObject:key]
回答by MrBr
Assuming the key is of type NSStringand keysis a dictionary, then you should instead be using something like:
假设键是类型NSString并且keys是字典，那么您应该使用以下内容：
if [keys containObject:key] {
// do something
}
