Cross-dissolve transitions interfering with page curls on UIPageController pages - ios

Question

I'm cross-dissolving between images on the pages of my UIPageController subclass. It is possible for a page to be turned while the transition is being applied. On occasion, the page being turned will become transparent mid-flip until the transition completes.
In the code below, the Page class is a subclass of UIViewController whose view has a UIImageView subview. PageController is my UIPageViewController subclass.
#implementation PageController : UIPageViewController
- (void)crossfadeToImage:(UIImage *)image
{
for (int i = 0; i < self.pages.count; i++) {
Page *page = self.pages[i]; // Pages fed to page controller in delegate
[UIView transitionWithView:page.view duration:duration options:UIViewAnimationOptionTransitionCrossDissolve | UIViewAnimationOptionAllowUserInteraction | UIViewAnimationOptionCurveEaseInOut animations:^{
page.image = image;
} completion:nil];
}
}
Page code goes as follows:
// HEADER
#interface Page : UIViewController
#property (strong, nonatomic) UIImage *image;
- (instancetype)initWithPageFrameSize:(CGSize)size image:(UIImage *)image;
#end
// IMPLEMENTATION
#implementation Page
- (void)loadView
{
UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0.0, 0.0, _pageFrameSize.width, _pageFrameSize.height)];
self.view = view;
}
- (UIImage *)image
{
return _imageView.image;
}
- (void)setImage:(UIImage *)image
{
if (!_imageView) {
_imageView = [[UIImageView alloc] initWithImage:image];
_imageView.frame = self.view.bounds;
[self.view addSubview:_imageView];
} else {
_imageView.image = image;
}
}
#end
I'm guessing the crossfade and the page curl animation are stacking in a weird way or something. Any ideas on how to prevent this "disappearing page" side-effect?

Answer 1

Turns out applying the animation to the imageView directly fixes this. Something like:
- (void)crossfadeToImage:(UIImage *)image
{
for (int i = 0; i < self.pages.count; i++) {
Page *page = self.pages[i]; // Pages fed to page controller in delegate
[UIView transitionWithView:page.**imageView** duration:duration options:UIViewAnimationOptionTransitionCrossDissolve | UIViewAnimationOptionAllowUserInteraction | UIViewAnimationOptionCurveEaseInOut animations:^{
page.**imageView**.image = image;
} completion:nil];
}
}
Still, any insights as to why it doesn't work the other way are welcome.