NSMutableArray of UIImages - view stays stuck with last image - objective-c

Question

I'm sure that I'm missing something terribly easy here...
I loop through the images just fine the first time, the indices reset and increment properly, but the UIView doesn't refresh and keeps the last image in the array showing. transitionFromView: automatically swaps the subviews, right? Do I need to implement the completion: option?
What am I missing? Here's the pertinent code:
- (id)initWithFrame:(CGRect)frame
{
NSInteger maxSlides = 12;
self = [super initWithFrame: frame];
if (self) {
//set up an array of images to be used for a flipbook
slides = [[NSMutableArray alloc] initWithCapacity: maxSlides];
for(NSInteger i=0; i<maxSlides; ++i) {
imageView = [[UIImageView alloc] initWithImage:
[UIImage imageNamed:[NSString stringWithFormat: #"muybridge%d.png", i]]];
[slides addObject: imageView];
}
index = 0; //default to first photo.
[self addSubview: [slides objectAtIndex: index]];
}
return self;
}
- (void) touchesEnded: (NSSet *) touches withEvent: (UIEvent *) event
{
//output indices for debugging. (yes, they increment properly)
NSLog(#"index = %d", index);
NSLog(#"currentIndex = %d", currentIndex);
NSLog(#"nextIndex = %d", nextIndex);
if (nextIndex <= 10) {
currentIndex = nextIndex;
} else {
currentIndex = 0;
}
nextIndex = currentIndex + 1;
//flipbook - tapping the image transitions to the next image in the array
[UIView transitionFromView: [slides objectAtIndex: currentIndex]
toView: [slides objectAtIndex: nextIndex]
duration: 0
options: UIViewAnimationOptionTransitionCurlUp
completion: NULL
];
}

Answer 1

What you're missing is this, from the docs on transitionFromView: toView:... :
fromView
The starting view for the transition. By default, this view is removed from its superview as part of the transition.
So it works, the first time through, but only one subview, the last one, remains after you've looked at them all. Look at the UIViewAnimationOptionShowHideTransitionViews option.

Answer 2

According to the Apple reference for UIView: transitionFromView: toView:... :
This method modifies the views in their view hierarchy only. It does not modify your application’s view controllers in any way. For example, if you use this method to change the root view displayed by a view controller, it is your responsibility to update the view controller appropriately to handle the change.
Maybe try calling the [yourView setNeedsDisplay] method right after.