UIScrollView with UIImageview and gestures using transitionFromView acting strange - objective-c

Question

I made a view which holds a UIScrollview:
self.scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(10, 65, 300, 188)];
//BackViews will hold the Back Image
BackViews = [[NSMutableArray alloc] init];
for (int i=0; i<BigPictures.count; i++) {
[BackViews addObject:[NSNull null]];
}
FrontViews = [[NSMutableArray alloc] initWithCapacity:BigPictures.count];
[self.pageControl setNumberOfPages:BigPictures.count];
Then I add several UIImageviews containing images:
//BigPictures holds objects of type UIImage
for (int i = 0; i < BigPictures.count; i++) {
UIImageView *ImageView = [[UIImageView alloc] initWithImage:[BigPictures objectAtIndex:i]];
ImageView.frame = [self.scrollView bounds];
[ImageView setFrame:CGRectMake(self.scrollView.frame.size.width * i, ImageView.frame.origin.y, ImageView.frame.size.width, ImageView.frame.size.height)];
//this saves the FrontView for later (flip)
[FrontViews insertObject:ImageView atIndex:i];
[self.scrollView addSubview:test];
}
// Detect Single Taps on ScrollView
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(flip)];
[self.scrollView addGestureRecognizer:tap];
self.scrollView.contentSize = CGSizeMake(self.scrollView.frame.size.width * BigPictures.count, self.scrollView.frame.size.height);
self.scrollView.pagingEnabled = YES;
self.scrollView.delegate = self;
Ok so far so good. Now the method which does the flipImage part:
- (void)flip {
int currentPage = self.pageControl.currentPage;
UIView *Back = nil;
if ([BackViews objectAtIndex:currentPage] == [NSNull null]) {
//CreateBackView is just creating an UIView with text in it.
Back = [self CreateBackView];
[BackViews replaceObjectAtIndex:currentPage withObject:Back];
[UIView transitionFromView:[[self.scrollView subviews] objectAtIndex:currentPage] toView:[BackViews objectAtIndex:currentPage] duration:0.8 options:UIViewAnimationOptionTransitionFlipFromLeft completion:NULL];
} else {
[UIView transitionFromView:[[self.scrollView subviews] objectAtIndex:currentPage] toView:[FrontViews objectAtIndex:currentPage] duration:0.8 options:UIViewAnimationOptionTransitionFlipFromRight completion:NULL];
[BackViews replaceObjectAtIndex:currentPage withObject:[NSNull null]];
}
[self.view addSubview:Back];
[self rebuildScrollView];
}
This is what rebuildScrollView does:
- (void)rebuildScrollView
{
for (UIView *subview in self.scrollView.subviews) {
[subview removeFromSuperview];
}
for (int i = 0; i < BigPictures.count; i++) {
if ([BackViews objectAtIndex:i] == [NSNull null]) {
[self.scrollView addSubview:[FrontViews objectAtIndex:i]];
} else {
[self.scrollView addSubview:[BackViews objectAtIndex:i]];
}
}
self.scrollView.contentSize = CGSizeMake(self.scrollView.frame.size.width * BigPictures.count, self.scrollView.frame.size.height);
self.scrollView.pagingEnabled = YES;
self.scrollView.delegate = self;
}
So the behavior is the following:
If I click on the first image (1 of 3 in scrollview) the effect is the way I want it, meaning the frontimage turns around and shows the empty (white) back with some text in the middle
If I click on the second image, the image turns but the back is completely empty showing the grey background of the window. If I scroll to the other images, the still show the front image (as expected)
Now I click on the third image and its the same as 1) great.
Current layout is now [BackView, Nothing, Backview)
Lets run that again. But now I click on the last image and its the same as 2) :(
Any ideas whats going wrong here?
EDIT: Some new findings. I doubled the amount of pictures and this is how Front and Backviews are placed (after flipping each one). P = Picture & B = Backview.
P_1(B_1) - actually the only correct one
P_2(empty - should be B_2)
P_3(B_2 - should be B_3)
P_4(empty - should be B_4)
P_5(B_3 - should be B_5)
P_6(empty - should be B_6)

Answer 1

Did a complete rebuild and now it works. Really strange because I used the exact same code.