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:

1. 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
2. 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)
3. Now I click on the third image and its the same as 1) great.
4. Current layout is now [BackView, Nothing, Backview)
5. 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.