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.