Question

I’m new to Objective-C and C in general. I’ve been looking around and I couldn’t find the solution to this issue. Any help would be appreciated.

I have the following global variables

CCSprite* BackgroundImage;
CCSprite* BackgroundGhost;
CCSprite* Globe;
CCSprite* Logo;

in my init I call a function and pass the global variables as parameters.

if(_ourDevice == iPad)
   {

       [self CustomCodeSetAssetForIpad:BackgroundImage ghost:BackgroundGhost TheGlobe:Globe AndTheLogo:Logo];


   }

Here is the code for CustomCodeSetAssetForIpad:

-(void) CustomCodeSetAssetForIpad:(CCSprite*) _Background ghost:(CCSprite*) _BackgroundGhosts TheGlobe:(CCSprite*)_Globes AndTheLogo:(CCSprite*) _Logos
{
    _Background = [CCSprite spriteWithFile:@"1028-768-sunray.png"];
    _BackgroundGhosts = [CCSprite spriteWithFile:@"1028-768-sunray.png"];
    _Globes = [CCSprite spriteWithFile:@"BigGlobe.png"];
    _Logos  = [CCSprite spriteWithFile:@"DefaultLogo.png"];

    [_BackgroundGhosts setAnchorPoint:CGPointMake(0.5, 0)];
    [_BackgroundGhosts setScale:2];
    [_BackgroundGhosts setOpacity:120];
    //[BackgroundGhost setPosition: CGPointMake(BackgroundGhost.position.x, BackgroundGhost.position.y-500)];

    [_BackgroundGhosts setPosition:CGPointMake([[CCDirector sharedDirector]winSize].width/2, -100)];

    [_Globes setAnchorPoint:CGPointMake(0.5, 0.5)];
    [_Globes setScale:0.7];
    [_Globes setPosition:CGPointMake([[CCDirector sharedDirector]winSize].width/2, -260)];



    [_Logos setPosition:CGPointMake([self CenterOfTheScreen].x, [[CCDirector sharedDirector]winSize].height-[[CCDirector sharedDirector]winSize].height*0.2)]; 
    [_Logos setScale:0.05];


}

The first few lines instantiate the global variables that were passed. However when the function is done, the reference to those objects are lost. I thought when you pass a pointer to a function, as the object is instantiated, it would retain its reference to the instantiated object. Am I missing something here?

Answer 1

Ah… Variables of type classname * are effectively references to instances of that class. So in your case, _Background is an instance reference passed in as an argument to your function. If you are trying to return multiple results from a function (via pointers), your arguments should really of type classname **, which is a pointer to a reference.

So the calling code would look like this:

CCSprite * background = nil ;
CCSprite * ghosts = nil ;
CCSprite * globes = nil ;
CCSprite * logos = nil ;

[ self customCodeSetAssetForIpad:&background ghosts:&ghosts globes:&globes logos:&logos ] ;

And your method looks like this:

-(void)customCodeSetAssetForIPad:(CCSprite**)background ghosts:(CCSprite**)backgroundhosts globe:globes logos:(CCSprite**)logos
{
    *background = [CCSprite spriteWithFile:@"1028-768-sunray.png"];
    // ... the rest of your code ...
}

Also, I took the liberty of making your method name and variable names more objective-c like (methods and variables begin with lowercase letters)

EDIT: I’d personally structure it like this:

//
// World... global things go in here
//

@interface World

@property ( nonatomic, readonly, strong ) CCSprite * background ;

+(id)theWorld // accessor to get the global world object

@end

@implementation World
@synthesize CCSprite * background = _background ;

static World * __theWorld = nil ; // global variable to hold our shared global World instance

+(void)load
{
    // when this class is loaded, create our global world object
    __theWorld = [ [ [ self class ] alloc ] init ] ;
}

+(id)theWorld
{
    return __theWorld ;
}

// return the background sprite, creating it if it hasn't be created yet
-(CCSprite*)background
{
    if ( !_background) { _background = [ CCSprite spriteWithFile:[CCSprite spriteWithFile:@"1028-768-sunray.png"] ; }
    return _background ;
}

@end