typedef enum type as key to NSDictionary?

Question

Are enums not allowed as keys for an NSMutableDictionary?

When I try to add to the dictionary via:

[self.allControllers setObject:aController forKey:myKeyType];

I get the error:

error: incompatible type for argument 2 of 'setObject:forKey:'

Typically, I use NSString as my key name which doesn't require a cast to 'id' but to make the error go away, I had do that. Is the casting the correct behavior here or are enums as keys a bad idea?

My enum is defined as:

typedef enum tagMyKeyType
{
  firstItemType = 1,
  secondItemType = 2
} MyKeyType;

And the dictionary is defined and properly allocated as such:

NSMutableDictionary *allControllers;

allControllers = [[NSMutableDictionary alloc] init];

Answer 1

No, you can't. Look at the method signature: id specifies an object. An enum type is a scalar. You can't cast from one to the other and expect it to work right. You have to use an object.

Answer 2

You can store the enum in an NSNumber though. (Aren't enums just ints?)

[allControllers setObject:aController forKey:[NSNumber numberWithInt: firstItemType]];

In Cocoa, const NSStrings are often used. In the .h you would declare something like:

NSString * const kMyTagFirstItemType;
NSString * const kMyTagSecondtItemType;

And in the .m file you would put

NSString * const kMyTagFirstItemType = @"kMyTagFirstItemType";
NSString * const kMyTagSecondtItemType = @"kMyTagSecondtItemType";

Then you can use it as a key in a dictionary.

[allControllers setObject:aController forKey:kMyTagFirstItemType];