CFStringRef appropriate for constant?

Question

I would like to define some constants and was thinking of using a #define construct, as follows:

#define kUpdateTeamNotification CFSTR("kUpdateTeamNotification")

My issue is that when I go to use it:

[[NSNotificationCenter defaultCenter] postNotificationName:kUpdateTeamNotification object:team];

I'm getting an Incompatible pointer types warning. I was under the impression CFSTR is essentially the same as @"" strings. Am I wrong in my understanding?

Answer 1

CFString and NSString are toll-free bridged so they are the same thing. (CFSTR is a macro to create a CFString). However you have to explicitly signal this to the compiler as the pointers have different types. Moreover, in ARC you will have to use a bridged cast, as you are crossing the boundaries between objects and C structs.

Here's how you use a bridged cast

[[NSNotificationCenter defaultCenter] postNotificationName:(__bridge NSString *)kUpdateTeamNotification object:team];

More info on bridged casts can be found here: NSString to CFStringRef and CFStringRef to NSString in ARC?

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However you might want to use a NSString literal as opposed to a CFStringRef and also to use a NSString *const (as explained in Constants in Objective-C) as opposed to a #define.

So your constant would become

Header file (.h)

FOUNDATION_EXPORT NSString *const kUpdateTeamNotification;

Implementation file (.m)

NSString *const kUpdateTeamNotification = @"kUpdateTeamNotification";