Question

I’m creating a game with Cocos2D for iPhone. The following expression appears in a few places around the code:

CGFloat screenCenter = [CCDirector sharedDirector].winSize.width / 2.0;

I’d like to put this in a constants file or similar such that the expression isn’t repeated all over the place. One idea is to put

#define SCREEN_CENTER [CCDirector sharedDirector].winSize.width / 2.0

in Constants.h and just import as necessary. However I’m under the impression that it’s better style/practice in Objective-C to use static const in some capacity.

How can I declare screenCenter in just one place using static const then re-use it throughout the code as necessary?

One potential benefit of this is doing the division only once instead of every time screen center is calculated.

Answer 1

This is not a compile-time expression, therefore you cannot make it a static const.

If you want to keep the #define, you need to wrap parens around it or you may introduce subtle bugs.

You may also want to consider using an inline function

inline CGFloat screenCenter() {
    return [CCDirector sharedDirector].winSize.width / 2.0f;
}

Or you could hang it off of CCDirector directly. Assuming you don’t own that class, you can use a category

@interface CCDirector (FunkyStuff)
- (CGFloat)screenCenter;
@end

@implementation CCDirector (FunkyStuff)
- (CGFloat)screenCenter {
    return self.winSize.width / 2.0f;
}
@end

...
x = [[CCDirector sharedDirector] screenCenter];

For added convenience you could even make it into a class method.