Use UIView tag as the key to an NSMutableDictionary

Question

I want to use a UIView tag as the key for an NSMutableDictionary. However, the compiler objects to me using an NSInteger as a key. I want to do the following:

NSInteger elementKey = _viewBeingDragged.tag;
myClass* element = [_model.elements objectForKey:elementKey];

How can I use elementKey as my dictionary key?

This question has been answered here: http://stackoverflow.com/questions/2992315/uiview-as-dictionary-key — gvaish, Aug 02 '16 at 22:18

score 2 · Answer 1 · answered Jun 07 '12 at 19:50

2

A NSInteger is not an object, and cannot be used as a key. You can wrap it in a NSNumber instead:

NSNumber* elementKey = [NSNumber numberWithInt:_viewBeingDragged.tag];
myClass* element = [_model.elements objectForKey:elementKey];

answered Jun 07 '12 at 19:50

Evan Mulawski

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score 0 · Answer 2 · answered Jun 07 '12 at 19:49

0

NSNumber* elementKey = [NSNumber numberWithInt:_viewBeingDragged.tag];

answered Jun 07 '12 at 19:49

unexpectedvalue

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score 0 · Answer 3 · answered Jun 07 '12 at 20:50

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I agree with both @Mario and @EvanMulawski but I prefer using strings for my key. Oh, and as for the reason that the compiler rejects the use of an NSInteger is that NSIntegers are pretty much equivalent to long ints.

NSString* elementKey = [NSString stringWithFormat:@"%i",_viewBeingDragged.tag];
//or NSNumber* elementKey = [NSNumber numberWithInt:_viewBeingDragged.tag];
myClass* element = [_model.elements objectForKey:elementKey];

answered Jun 07 '12 at 20:50

erran

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Yeah, as I wrote, I also prefer strings, since it's safe then to use kvc. – Mario Jun 07 '12 at 20:55

score 0 · Answer 4 · answered Dec 06 '16 at 11:23

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Wrap it in an NSNumber literal.

myClass* element = _model.elements[@(_viewBeingDragged.tag)];

And assignment:

NSInteger tag = view.tag;
myClass *value;
_model.elements[@(tag)] = value;

answered Dec 06 '16 at 11:23

kkodev

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score -3 · Accepted Answer · edited Jun 14 '12 at 02:59

-3

Rather create an NSString for the key, although you could use any NSCopying conform object:

NSString *key = [NSString stringWithFormat: @"%d",elementKey];

edited Jun 14 '12 at 02:59

erran

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answered Jun 07 '12 at 20:43

Mario

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Your code snippet is incorrect, since you aren't passing an argument to match the "%d" format specifier. Also, using a string as a key when `NSNumber` would be a more natural fit is a bad idea and potentially unsafe. For example, for 64-bit, "%d" is not the right specifier for `NSInteger`, so you could get the same string for two different tags. – Ken Thomases Jun 09 '12 at 11:36

Use UIView tag as the key to an NSMutableDictionary

5 Answers5