Image not centered vertically in scrollview - objective-c

Question

What am I missing? The inner scrollview and the image view fill the entire screen. But somehow my image is not centered. The top left corner of the image starts in the center of the view, but I would like to have the image nicely centered. Also during zooming.
-(void)prepareScrollView
{
for(int i =0;i<[self.layoverPhotoAssets count];i++){
PHAsset *asset = self.layoverPhotoAssets[i];
FMImageZoomViewController *zoomController = [[FMImageZoomViewController alloc] init];
// UIImageView *imageView = [[UIImageView alloc] init];
int x = self.scrollView.frame.size.width * i;
zoomController.view.frame = CGRectMake(x, 0, self.scrollView.frame.size.width, self.scrollView.frame.size.height);
//zoomController.view.frame = CGRectMake(0,0,self.view.bounds.size.width,self.view.bounds.size.height);
[self.scrollView addSubview:zoomController.view];
zoomController.zoomScroller.delegate = self;
zoomController.imageView.tag = 1;
[self.zoomControllers addObject:zoomController];
PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
options.resizeMode = PHImageRequestOptionsResizeModeFast;
options.deliveryMode = PHImageRequestOptionsDeliveryModeHighQualityFormat; //I only want the highest possible quality
options.synchronous = NO;
options.networkAccessAllowed = YES;
[[PHImageManager defaultManager] requestImageForAsset:asset targetSize:zoomController.zoomScroller.frame.size contentMode:PHImageContentModeAspectFill options:options resultHandler:^(UIImage *result, NSDictionary *info) {
dispatch_async(dispatch_get_main_queue(), ^{
if(result){
zoomController.imageView.image = result;
zoomController.imageView.backgroundColor = [UIColor redColor];
}
});
}];
//self.scrollView.contentSize= ;
}
[self.scrollView setContentSize:CGSizeMake(self.scrollView.frame.size.width * [self.layoverPhotoAssets count], 0)];
[self scrollToAsset:self.selectedAsset];
}

Answer 1

Consider:
zoomController.view.frame = CGRectMake(x, 0, self.scrollView.frame.size.width, self.scrollView.frame.size.height);
[self.scrollView addSubview:zoomController.view];
That cannot be right. If zoomController.view is to be a subview of self.scrollView, its frame within self.scrollView is in terms of the bounds of self.scrollView, not the frame of self.scrollView.

Answer 2

Solved it like this:
-(void)prepareScrollView
{
for(int i =0;i<[self.layoverPhotoAssets count];i++){
PHAsset *asset = self.layoverPhotoAssets[i];
FMImageZoomViewController *zoomController = [[FMImageZoomViewController alloc] init];
// UIImageView *imageView = [[UIImageView alloc] init];
int x = self.scrollView.frame.size.width * i;
zoomController.view.frame = CGRectMake(x, 0, self.scrollView.bounds.size.width, self.scrollView.bounds.size.height);
//zoomController.view.frame = CGRectMake(0,0,self.view.bounds.size.width,self.view.bounds.size.height);
[self.scrollView addSubview:zoomController.view];
zoomController.zoomScroller.delegate = self;
[self.zoomControllers addObject:zoomController];
PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
options.resizeMode = PHImageRequestOptionsResizeModeExact;
options.deliveryMode = PHImageRequestOptionsDeliveryModeHighQualityFormat; //I only want the highest possible quality
options.synchronous = NO;
options.networkAccessAllowed = YES;
[[PHImageManager defaultManager] requestImageForAsset:asset targetSize:zoomController.zoomScroller.bounds.size contentMode:PHImageContentModeAspectFit options:options resultHandler:^(UIImage *result, NSDictionary *info) {
dispatch_async(dispatch_get_main_queue(), ^{
if(result){
zoomController.imageView = [[UIImageView alloc] initWithImage:result];
zoomController.imageView.frame = zoomController.zoomScroller.bounds;
[zoomController.imageView setContentMode:UIViewContentModeScaleAspectFit];
zoomController.imageView.clipsToBounds = YES;
[zoomController.imageView setCenter: self.scrollView.center];
zoomController.imageView.tag = 1;
[zoomController.zoomScroller addSubview:zoomController.imageView];
// zoomController.imageView.contentMode = UIViewContentModeCenter;
// if (zoomController.imageView.bounds.size.width > result.size.width && zoomController.imageView.bounds.size.height > result.size.height) {
// zoomController.imageView.contentMode = UIViewContentModeScaleAspectFit;
// }
}
});
}];
//self.scrollView.contentSize= ;
}
[self.scrollView setContentSize:CGSizeMake(self.scrollView.frame.size.width * [self.layoverPhotoAssets count], 0)];
[self scrollToAsset:self.selectedAsset];
}