Using an int as an NSDictionary key?

Question

I'm trying to access my dictionary object. Here's my code:

int tag = object.tag;
CGPoint point = [[self.dict objectForKey:tag] CGPointValue];

The problem is objectForKey is supposed to take an Objective-C object, not an int. I tried wrapping tag into an NSNumber with [NSNumber numberWithInt:tag] and passing that into objectForKey: but it returns a null object.

Any ideas? Thanks

Answer 1

I use NSNumbers without problems, but must avoid the usual setObject: forKey: or setValue: forKey: methods. That would create a warning.

No warning, however, is created (and the code works as intended) with

NSMutableDictionary *myDict = [[NSMutableDictionary alloc] init];
NSNumber *key = @1;
id *myObject  = [your code here];
myDict[key]   = myObject;

Retrieval is straightforward:

myObject = myDict[key];

Answer 2

If you are using numbers as strings for dictionary keys, you should turn the int into a NSString or NSNumber to use it as a dictionary key. Here's how to do it for a string:

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

As @Hughes BR mentions in a comment, the requirement for the key object is that it must conform to the NSCopying protocol.