array crashing at index which is in bounds? - objective-c

Question

Can anyone help me out with explaining why my array is crashing.
Basically I have two buttons which change the image in the imageView.
h:
#interface CaseStudySecondPageViewController : UIViewController
{
//scroller and back and forward buttons for custom control.
__weak IBOutlet UIScrollView *scroller;
__weak IBOutlet UIButton *back;
__weak IBOutlet UIButton *forward;
//app delegate to return the selected case study from the other controller.
AppDelegate *del;
//variables for displaying the case studies
NSArray *myImageArray;
NSInteger localSelctorInt;
}
//setup a IBOutlet to allow the image to be changed.
#property (weak, nonatomic) IBOutlet UIImageView *logoImage;
#end
m:
update method:
-(void)Updater
{
[logoImage setImage:[myImageArray objectAtIndex:localSelctorInt]];
}
previous and next buttons:
//returns to previous image if back button is clicked.
-(void) back:(id)sender
{
if (localSelctorInt > 0)
{
localSelctorInt--;
}
else
{
localSelctorInt = 0;
}
[self Updater];
}
//returns to next image if forward button is clicked. increase 7 if array size changes.
//1 removed from int as in starts at 1 and array starts at 0.
-(void) forward:(id)sender
{
if (localSelctorInt < 7)
{
localSelctorInt++;
}
else
{
localSelctorInt = 7;
}
[self Updater];
}
and finally my image array is declared in:
- (void)viewDidLoad
{
[super viewDidLoad];
//setup the delegate to allow access to the int which was modified on the page before.
del = [[UIApplication sharedApplication] delegate];
//assign a local variable to the int from the previous page.
localSelctorInt = *(del.selectorInt);
//create back and forward buttons as UIButtons first.
[back addTarget:self action:#selector(back: ) forControlEvents:UIControlEventTouchUpInside];
[forward addTarget:self action:#selector(forward:) forControlEvents:UIControlEventTouchUpInside];
//pass the ui buttons into ui bar items.
UIBarButtonItem *UIBack = [[UIBarButtonItem alloc] initWithCustomView:back];
UIBarButtonItem *UIForward = [[UIBarButtonItem alloc] initWithCustomView:forward];
//add these to an array (notice item"s").
self.navigationItem.rightBarButtonItems = [NSArray arrayWithObjects:UIForward, UIBack, nil];
//initialize the array with all of the images for the case studies logos.
myImageArray = [NSArray arrayWithObjects:
[UIImage imageNamed:#"Logo_Arm.png"],
[UIImage imageNamed:#"Logo_Fife"],
[UIImage imageNamed:#"Logo_Findel.png"],
[UIImage imageNamed:#"Logo_BirkBeck.png"],
[UIImage imageNamed:#"Logo_NHS_Dudley.png"],
[UIImage imageNamed:#"Logo_NHS_Kensignton.png"],
[UIImage imageNamed:#"Logo_Yorkshire_Water.png"],
[UIImage imageNamed:#"Logo_Uni_Hertfordshire.png"],
nil];
//call update method once to load the first image selected from the previous page.
[self Updater];
}
now my app crashes when it trys to index the 4th image (3rd in the array):
* Terminating app due to uncaught exception 'NSRangeException', reason: '* -[__NSArrayI objectAtIndex:]: index 3 beyond bounds [0 ..
2]'
It's probably something really simple, but id appreciate your help, cheers.

Answer 1

If you look at your exception, it says that your array contains 3 objects only ( ... bounds [0..2] ... ). So, my guess is that your fourth image doesn't exist ... Check spelling of [UIImage imageNamed:#"Logo_BirkBeck.png"]. Does this image really exist? It returns nil, list of objects is nil terminated, so, your array does contain 3 images only instead of 8 images.
Side Note: Don't use magic constants like localSelctorInt < 7. Always rely on real number of elements in array (_myImageArray.count). It's a way to hell ...
2nd Side Note: Don't declare ivars without underscore prefix. Do use something like this _myImageArray for ivar name.

Answer 2

I guess its due to not allocating the array
myImageArray = [[NSArray alloc] initWithObjects:
[UIImage imageNamed:#"Logo_Arm.png"],
[UIImage imageNamed:#"Logo_Fife.png"],
[UIImage imageNamed:#"Logo_Findel.png"],
[UIImage imageNamed:#"Logo_BirkBeck.png"],
[UIImage imageNamed:#"Logo_NHS_Dudley.png"],
[UIImage imageNamed:#"Logo_NHS_Kensignton.png"],
[UIImage imageNamed:#"Logo_Yorkshire_Water.png"],
[UIImage imageNamed:#"Logo_Uni_Hertfordshire.png"],
nil];