UiCollectionView freezes starting at a given index - ios

Question

According to some answers I found in Stackoverflow, I should use this piece of code:
- (void)viewDidLayoutSubviews {
[super viewDidLayoutSubviews];
[self.collectionView scrollToItemAtIndexPath:selectedRow atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];
}
but the scrolling freezes, so I have to set it up this way:
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
self.navigationItem.title = [NSString stringWithString:barTitle];
self.automaticallyAdjustsScrollViewInsets = NO;
//Download JSON
NSError *error=nil;
NSURL *url = [NSURL URLWithString:urlToFollow];
data = [NSMutableData dataWithContentsOfURL: url options:NSDataReadingMappedIfSafe error:&error];
NSDictionary *dictionary = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error];
NSArray *response = [dictionary objectForKey:#"items"];
articlesArray = [[NSArray alloc] initWithArray:response];
//sizes
CGFloat window_height = ([self window_height]-70.0);
CGFloat window_width = [self window_width];
CGRect frame = CGRectMake((window_width/2)-15.0f , window_height, 30.0f , 15.0f);
self.pageControl = [[UIPageControl alloc]initWithFrame:frame];
UICollectionViewFlowLayout *layout = (id) self.collectionView.collectionViewLayout;
layout.itemSize = self.collectionView.frame.size;
// Add a target that will be invoked when the page control is changed by tapping on it
[self.pageControl
addTarget:self
action:#selector(pageControlChanged:)
forControlEvents:UIControlEventValueChanged
];
// Set the number of pages to the number of pages in the paged interface
// and let the height flex so that it sits nicely in its frame
if (articlesArray.count >8) {
self.pageControl.numberOfPages = 10;
}else if (articlesArray.count <8){
self.pageControl.numberOfPages =[articlesArray count];
}
self.pageControl.autoresizingMask = UIViewAutoresizingFlexibleHeight;
[self.view addSubview:self.pageControl];
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
[self.collectionView scrollToItemAtIndexPath:selectedRow atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];
}
#pragma mark uicollectionview
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView{
return 1;
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
return [articlesArray count];
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
LOArcticlesCustomCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"MyCell" forIndexPath:indexPath];
[cell.imageView setImageWithURL:[NSURL URLWithString:[[articlesArray objectAtIndex:indexPath.row]objectForKey:#"photoUrl"]]placeholderImage:[UIImage imageNamed:#"simboloLakari29.png"]];
index= indexPath.row;
cell.lblMake.text = [NSString stringWithString:[[articlesArray objectAtIndex:indexPath.row]objectForKey:#"marca"]];
cell.lblMake.lineBreakMode = NSLineBreakByWordWrapping;
cell.lblModel.text = [NSString stringWithString:[[articlesArray objectAtIndex:indexPath.row]objectForKey:#"modelo"]];
cell.lblModel.lineBreakMode = NSLineBreakByWordWrapping;
cell.lblPrice.text = [NSString stringWithString:[[articlesArray objectAtIndex:indexPath.row]objectForKey:#"precio"]];
cell.lblOrder.text = [NSString stringWithFormat:#"%ld de %ld", (unsigned long)indexPath.row+1, (unsigned long)articlesArray.count];
return cell;
}
#pragma mark page control
- (void)pageControlChanged:(id)sender
{
UIPageControl *pageControl = sender;
CGFloat pageWidth = self.collectionView.frame.size.width;
CGPoint scrollTo = CGPointMake(pageWidth * pageControl.currentPage, 0);
[self.collectionView setContentOffset:scrollTo animated:YES];
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
CGFloat pageWidth = self.collectionView.frame.size.width;
self.pageControl.currentPage = self.collectionView.contentOffset.x / pageWidth;
}
- (CGFloat) window_height {
return [UIScreen mainScreen].applicationFrame.size.height;
}
- (CGFloat) window_width {
return [UIScreen mainScreen].applicationFrame.size.width;
}
But the CollectionView goes from index=0 to the desired index and it's very annoying.
Any suggestion?