Question

I am in ViewController, trying to access a method in object “cat” owned by object “backgroundpicture”. ViewController has an instance of backgroundpicture.

The method/message in “cat.h”:

@interface Cat : NSObject
    -(BOOL)checkIfTouchHit:(float) xx :(float) yy; 
@end

“Cat.m”:

- (BOOL)checkIfTouchHit:(float) xx :(float) yy{
    NSLog(@"Inside checkIfTouchHit");
    return YES;
}

“BackGroundPicture.h”:

#import "Cat.h"

@interface BackGroundPicture : NSObject
    @property (strong) Cat * katt;
@end

“BackGroundPicture.m”:

@implementation BackGroundPicture
    @synthesize katt = _katt
@end

“ViewController.m”:

@interface ViewController ()
@property (strong) BackGroundPicture * bakgrunnsbilde;
@end

@implementation BackGroundPicture
@synthesize bakgrunnsbilde = _bakgrunnsbilde;
- (void)viewDidLoad
{...
[[self.bakgrunnsbilde katt] checkIfTouchHit :(float)touchLocation.x :(float)touchLocation.y]   
...}

The string inside the method “checkIfInside” in cat will not show up. I also tried
[_bakgrunnsbilde katt]…
but with the same lack of result, and I believe this is compiled the same way. I am wondering what I am missing here, and hope someone can help. Thanks 🙂

edit I forgot to add a few lines from my BackGroundPicture.m. It is a method run on start from the ViewDidLoad in ViewController. It is like this in BackGroundPicture.m:

- (void)createObjects {    
Cat * katt = [[Cat alloc] init];
}

it is called from ViewController.m like so:

- (void)viewDidLoad
{
[_bakgrunnsbilde createObjects];
}

I know that this get executed. I hope this edit makes sense, my head is ruined after a long day 🙂 Going to check back tomorrow morning.

Answer 1

It will work, but BackGroundPicture.m needs to allocate a cat first.

So in BackGroundPicture.m, do this:

- (id)init {

    self = [super init];
    if (self) {
        _katt = [[Cat alloc] init];
    }
    return self;
}

In general, remember to allocate objects before you use them. You may also need to create a BackGroundPicture, too as Valentin points out. In viewDidLoad, do this:

bakgrunnsbilde = [[BackGroundPicture alloc] init];