Objective-C for Dummies: How do I get a value out of NSDictionary?

Question

so I'm having the most difficult of time pulling values out of an NSDictionary. Right now I just have a dictionary that is populated from a JSON call and it only contains a key named 'Success' with a value of 0 or 1.

How do I do a conditional on that value to check if its 0 or 1? I've tried a bunch of things, but I'm not getting anywhere. Here's my current code:

[[jsonDictionary objectForKey:@"Success"] isEqualToNumber:1]

I'm getting passing argument 1 of 'isEqualToNumber:' makes pointer from integer without a cast' as a warning, and the app crashes when it hits that line anyway.

And a subquestion, what's the difference between objectForKey and valueForKey? Which one should I use by default?

Anyway, this noob in Objective-C would truly appreciate some help on this. Thanks in advance!

Differences between `objectForKey` and `valueForKey` already has been discussed [here](http://stackoverflow.com/questions/4489684/difference-valueforkey-objectforkey) — Martin Babacaev, Jan 28 '11 at 21:29
@Martin Nice answer there. I’ll favourite that question to keep it handy. — , Jan 28 '11 at 21:37

score 4 · Accepted Answer · answered Jan 28 '11 at 21:33

Since dictionaries contain Objective-C objects, an entry containing a number is an NSNumber instance. NSNumber provides a convenience method, -intValue, for extracting its underlying int value:

if ([[jsonDictionary objectForKey:@"Success"] intValue] == 1) { … }

Note that NSNumber has other convenience methods for extracting its underlying value as other C data types.

In most cases, you should use -objectForKey: instead of -valueForKey:. The former is the canonical method to obtain an entry in the dictionary and is declared in NSDictionary. The latter is declared in NSObject and is used in Key-Value Coding contexts, where the key must be a valid KVC key, and there’s additional processing — for instance, if you’re using -valueForKey: in a dictionary with a key that starts with @, that character is stripped from the key and [super valueForKey:key] is called.

you've saved me once again, thanks! The conditional works and now I gotta figure out how to act on. Objective-C has been a *slow* learning experience for me... — Gup3rSuR4c, Jan 28 '11 at 21:44
@Alex Cheers. Be warned that `-intValue` will return `0` if the key is not in the dictionary, though. In some cases I first grab the object from the dictionary (e.g. `NSNumber *success = [jsonDictionary objectForKey:@"Success"];`) and test if it’s different from `nil` to make sure the key was available in the dictionary in the first place. Good luck with your project! — , Jan 28 '11 at 21:54

score 2 · Answer 2 · answered Jan 28 '11 at 21:30

2

The number 1 is not an object pointer. Use an NSNumber instance instead if you want to use a number in an NSDictionary.

[[jsonDictionary objectForKey:@"Success"]
 isEqualToNumber:[NSNumber numberWithInteger:1]]

answered Jan 28 '11 at 21:30

Jeffrey Hantin

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vikingosegundo · Answer 3 · 2011-01-28T21:33:19.230

1

 [[jsonDictionary objectForKey:@"Success"] isEqualToNumber: [NSNumber numberWithInt:1]]

Number and Value Programming Topics: Using Numbers
NSNumber: What is the point ?

edited Jan 28 '11 at 21:33

answered Jan 28 '11 at 21:27

vikingosegundo

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handiansom · Answer 4 · 2017-03-24T13:44:29.197

0

You can get the value of dictionary in different ways like checking the value first.

Solution 1: Using simple if statement.
int value = 0;
if ([[jsonDictionary objectForKey:@"Success"]intValue]==1){
    value = [[jsonDictionary objectForKey:@"Success"]intValue];
}

Solution 2: Using ternary operator
value = ([[jsonDictionary objectForKey:@"Success"]intValue]==1) ? 1:0;

edited Mar 24 '17 at 13:44

answered Mar 24 '17 at 13:39

handiansom

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Objective-C for Dummies: How do I get a value out of NSDictionary?

4 Answers4