loop Nsmutable arrray of uiimages from end to beginning - objective-c

Question

I have an NSMUtable array of images where a different image is displayed with a previous and a next button, but when I get to the end of the array the simulator crashes. I want to loop the end of the array to the beginning so that when I get to the end of the array of images when I hit the next button again it loops back to the first image, also when Im at the first image if I hit the previous button it loops to the last image with no crashes

Answer 1

What you want is a circular array, which is easy to implement using a standard NSMutableArray. For instance, say you store your images in an array called imageArray and use a simple variable to keep track of the index of your current image, like:
int currentImageIndex = 0;
...then you might implement nextImage and previousImage like:
- (UIImage*) nextImage {
currentImageIndex = (currentImageIndex + 1) % [imageArray count];
return [imageArray objectAtIndex:currentImageIndex];
}
- (UIImage*) previousImage {
currentImageIndex--;
if (currentImageIndex < 0) {
currentImageIndex = [imageArray count] - 1;
}
return [imageArray objectAtIndex:currentImageIndex];
}
Then just use nextImage and previousImage whenever you want to step through the array, and problem solved.

Answer 2

Simple enough to do. all you need to do is create a check to see if you're on the last element, and if so, set your tracker (like count or i etc) to 0 again,
Heres the psudo code
//set index
if ( array [ index ] == len(array) - 1) //at end
{
index = 0
}
if(array [index] == -1)//at beginning
{
index = len(array) -1
}
// do something with array[index]

Answer 3

I want to propose this solution:
A property for the selected UIImage, a NSInteger property to hold the current index.
-(IBAction) nextButtonTapped:(id)sender
{
self.currentIndex = self.currentIndex++ % [self.images count];
self.selectedImage= [self.images objectAtIndex:self.currentIndex];
[self reloadImageView];
}
-(IBAction) previousButtonTapped:(id)sender
{
self.currentIndex--;
if (self.currentIndex < 0)
self.currentIndex += [self.images count];
self.selectedImage= [self.images objectAtIndex:self.currentIndex];
[self reloadImageView];
}
-(void)reloadImageView
{
//do, what is necessary to display new image. Animation?
}