Alternativa a NSDictionary con un solo objeto/clave

Say I want to have an item that holds a string as a value to a key, using a dictionary I would write:

[NSDictionary dictionaryWithObject:@"someString" forKey:@"stringKey"];

I'm asking how to do this without a dictionary (ambiguous, the programmer needs to know the key) or an object (overkill for this thin object, no need for methods), something more in the lines of structs, I tried structs before, but I haven't seen any struct in iOS that uses chars as struct items, so I'm not sure that this is the way to go. The result should be similar to this:

replacement.key = value;

¿Alguna idea?

preguntado el 31 de julio de 12 a las 15:07

¿Por qué no puedes usar NSDictionary? -

What are you trying to achieve? Can you give an example or some background? -

4 Respuestas

A small data object is seldom overkill unless you have a very specialized problem. For example, if you had many thousands of these objects, and particularly if you needed to create and destroy them quickly, and you had profiled your app and discovered that the objects themselves were a real problem, then you should consider not using simple data objects. But in the general case, you should use simple data objects.

Respondido 31 Jul 12, 15:07

I am not sure, if it what you want, but you puede Usar una struct:

 typedef struct {
    __unsafe_unretained NSString* key;
 } foo;

 foo bar;
 NSString* foobar = @"Hello";
 bar.key = foobar;

Attention, there is no reason for ARC not to dispose this value. But if you have a strong reference to the value, you can use it.

Respondido 31 Jul 12, 15:07

How would one use this to get a value from that key? - James Webster

My understanding was, that the OP want to access a component by name, i.e., like in a "normal" C struct. key is here simply the símbolo to address the component of the struct, not a key as in KVC. - Matías

The above is extremely dangerous. The string can be discarded at any time and your key would become a dangling pointer. While possible, it should be strongly avoided unless there is no other solution. There's a reason that the word "unsafe" is right there in the text. - rober napier

will using chars instead of NSString will make a difference? - Yogev Shelly

If you use char* rather than NSString, then yes, that's just C, so it will work. But you must memory manage the char* (or use a fixed-length string). This is a lot of overhead to avoid a little overhead. - rober napier

A thin object with @property y @synthesize will save you any pain of creating methods. All instance variable will be created and modified without any code of yours.

Such an object definition would hardly be larger than a struct, and, being a subclass of NSObject, it can be put in any array or other framework containers which only accept NSObject subclasses. You won't be able to do that with structs.

If you use XCode 4.4 (for Mac development) or 4.5 (for iOS), you'll even be able to drop @synthesize y solo tener @property.

Only if you're really tight on performance and need to get away from NSObject hierarchy you should be considering dropping it and using C structs.

Respondido 31 Jul 12, 16:07

Why don't you just use the dictionary but create a set of NSString constants that will work as the key? Then there will be less ambiguity.

For example consider Apple's key constant used for retrieving a localized string from a NSError's userInfo dictionary NSLocalizedDescriptionKey. Many other keys are used as well to retrieve specific parts of information and because these keys are constants, they're easy to use in Xcode (autocompletion). Another example of using string constants to retrieve values out of an NSDictionary could be NSFileManager.

Additionally, just using an object should be fine as well, in most cases the 'overhead' should be negligible - certainly not anything a user would notice. At the very least, please don't try to prematurely optimize your code for situations that podría ever happen in the very far future ...

Respondido 12 Abr '17, 08:04

i usually go with #define for key but that would work as well, you still need to let the programer know that these are the right key. so many Stack Overlfow questions can be averted - Yogev Shelly

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