使用“生成的字符串” (stringWithFormat) 作为 NSDictionary 的键
我想做这样的事情：
#define GETKEY (a) ([NSString stringWithFormat:@"%d",a])
NSMutableDictionary *mutableDictionay=[NSMutableDictionary dictionary];
//population of dictionary
[mutableDictionary setObject:anObject forKey:GETKEY(someIntValue)];
//... then retrive the object
[mutableDictionary getObjectForKey:GETKEY(someIntValue)];
但我担心 stringWithFormat 方法返回具有相同值的 NSString 的不同实例，我的意思是有 2 个字符串：“0”和另一个值为“0”的实例。我想知道这是否是获取和设置字典中对象的安全方法。如果不是，什么其他方法可能是从整数“生成”密钥对象的最佳方法？
I would like to do something like this:
#define GETKEY (a) ([NSString stringWithFormat:@"%d",a])
NSMutableDictionary *mutableDictionay=[NSMutableDictionary dictionary];
//population of dictionary
[mutableDictionary setObject:anObject forKey:GETKEY(someIntValue)];
//... then retrive the object
[mutableDictionary getObjectForKey:GETKEY(someIntValue)];
But I'm concerned the stringWithFormat method returns a different instance of NSString with the same value, I mean like having, 2 strings: "0" and another instance with value "0". I would like to know if this is a safe way to get and set the objects in the dictionary. If not, what other way could be the best way to "generate" a key object from an integer?
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是的，您正在做的事情是完全安全的，并且会按预期工作。字典的键在获取和设置时使用 isEqual 方法进行比较，该方法仅检查字符串的值，而不检查它们的地址。 “0”和“0”是相等的，无论它们是否是同一个实例。
您可以在 NSObject 协议参考。请注意，
==和isEqual不是同一件事（==检查地址，isEqual检查值）。Yes, what you're doing is perfectly safe, and will work as expected. The keys of a dictionary when getting and setting are compared using the
isEqualmethod, which only checks the values of the strings, and not their addresses. "0" and "0" are equal, regardless of whether they are the same instance or not.You can read more about the
isEqualdocumentation in the NSObject Protocol Reference. Just be aware that==andisEqualare not the same thing (==checks addresses,isEqualchecks values).如果您期望所有这些都是数字，您应该考虑使用 NSNumber，但它也可以与 NSString 一起使用。 NSDictionary 键必须符合 NSCopying 协议，并且使用 isEqual: 选择器来比较键。
You should consider using NSNumber if expect all of them to be numbers but it will work with NSString also. The NSDictionary keys must conform to NSCopying protocol and keys are compared using the isEqual: selector.