UICollectionview non parallel animation - ios

Question

My question in short: how can this effect on UICollectionView be achieved?
I have a collectionview with a custom layout that is similar to a gridlayout. Now when I enter the collectionview controller I want the cells to have a nice animation.
I know I can implement - initialLayoutAttributesForAppearingItemAtIndexPath: etc and call performBatchUpdates on the collectionview. Now when I do this all the animations are executed in parallel (like calling UIView animate). In a lot of apps I see effects where this isn't done in paralell like the philips hue app on iPhone, the effect can be seen in the movie posted at the top. One thing I could think if is that instead of inserting all the objects here the rows are added separatly, so for instance all rows are looped and dispatched after a certain interval next from each other.
Anyway if someone could hint me what the best approach is for achieving this effect or knows about a sample that does something similar I would be very grateful.

Answer 1

Here's one way of doing it: (I felt kinda dirty after writing this.. but it works)
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
myCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"cell" forIndexPath:indexPath];
cell.myPic.image = [UIImage imageNamed:[NSString stringWithFormat:#"%d.jpg",indexPath.row]];
CGRect frame = cell.myPic.frame;
frame.origin.y = cell.myPic.frame.origin.y + 40;
cell.myPic.frame = frame;
cell.myPic.alpha = 0;
[cells addObject:cell];
return cell;
}
- (IBAction)Run:(UIButton *)sender
{
for (int i=0; i<[cells count]; i++)
{
myCell *cell = [cells objectAtIndex:i];
[UIView animateWithDuration:0.15 animations:^() {
CGRect frame = cell.myPic.frame;
frame.size.width = 80;
frame.origin.y = cell.myPic.frame.origin.y - 40;
cell.myPic.frame = frame;
cell.myPic.alpha = 1;
}completion:^(BOOL finished){}];
[[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.05]];
}
}