How can I use an integer value as 'key' to set value in NSMutableDictionary?

Question

How can I use an integer value as 'key' to set a float value in NSMutableDictionary ?

Bentinck

As a potential aid to Google searchers: XCode will give the error Expected method to write array element not found on object of type 'NSMutableDictionary * on an attempt to use a raw int or an NSInteger as an NSMutableDictionary key. – Forras

Answer 1

As NSDictionarys are only designed to deal with objects, a simple way to do this is to wrap the integer and float in a NSNumber object. For example:

NSMutableDictionary *testDictionary = [[NSMutableDictionary alloc] init];
[testDictionary setObject:[NSNumber numberWithFloat:1.23f]
                   forKey:[NSNumber numberWithInt:1]];
NSLog(@"Test dictionary: %@", testDictionary);

[testDictionary release];

To extract the relevant value, simply use the appropriate intValue, floatValue, etc. method from the NSNumber class.

Selle

It's telling me that the key must be NSString*, and searching through NSKeyValueCoding.h it looks like all the methods expect strings. Has something changed in the SDK? – Wooton

Answer 2

You can use NSMapTable as it supports integer keys and/or values directly. No need to box/unbox through NSNumber, but it is also slightly more difficult to set up and use.

Fachanan

NSMapTable is only available in iOS 6 and later. – Rapier

NSMapTable holds weak references, which may or may not be what you want. That is different than NSDictionary, though. – Well

NSMapInsert isn't available on iOS. Is there a better way to set an integer value other than something like this: [map setObject:(__bridge id)((void *)myInt) forKey:myKey];? I'm assuming the valueOptions were set to NSPointerFunctionsIntegerPersonality | NSPointerFunctionsOpaqueMemory. – Orphrey

Answer 3

It needs to be an object, so use [NSNumber numberWithInt:myInteger] instead.

Then, retrieve it with -integerValue

Alkmaar

The integerValue method returns an NSInteger object, not an int. :-) – Selle

Ouch, that should be -intValue. Thanks middaparka – Alkmaar

@middaparka: NSInteger is not an object. – Rhona

@Simon yes haha, but anyway I decided to point -intValue because I think the OP needs the primitive. – Alkmaar

@Simon Ah.. yes. It's a foundation data type. My bad. (Feel free to ignore the above.) :-) – Selle