ScrollView addSubview: very slow - iphone

Question

I am using a scrollview to display a viewcontrollers view. if the user reaches the end of the cached views my method reloads the new views. My NSLogs say that the method is finished but it takes additional 5 seconds to display the view.
I think that the [scrollView addSubview:vc.view] is very very slow but I found nothing to improve it.
the whole method gets called in -(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
scrollView.userInteractionEnabled = NO;
UIActivityIndicatorView *activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
[activityIndicator setFrame:CGRectMake((320.f*index)+135.f, 151, 50, 50)];
[activityIndicator setHidesWhenStopped:YES];
[activityIndicator startAnimating];
[scrollView addSubview:activityIndicator];
MBBAppDelegate *delegate = (MBBAppDelegate *)[UIApplication sharedApplication].delegate;
[delegate fetchDealsWithFilter:dealFilter fromIndex:index toIndex:(index+3) onSuccess:^(id object){
MBBDealList *list = object;
int i = 0;
ProductDetailViewController *vc;
for (MBBDeal *deal in [list deals]) {
NSLog(#"start %i",i);
int indexInArray = i;//[list.deals indexOfObject:deal];
if (indexInArray+index >= numDeals) {
return;
}
vc = [[ProductDetailViewController alloc] init];
//fetch the deal and insert
vc.numberOfDeals = numDeals;
vc.dealIndex = index+1+indexInArray;
vc.dealFilter = dealFilter;
vc.deal = deal;
vc.view.frame = CGRectMake(320.f*(index+indexInArray), 0.f, 320.f, 436.f);
[scrollView addSubview:vc.view];
[productDetailViewControllers insertObject:vc atIndex:(index+indexInArray)];
i++;
}
[activityIndicator stopAnimating];
scrollView.userInteractionEnabled = YES;
}];
}
Does anyone know how I can improve my method?

Answer 1

What I can understand from your problem is that, the activity indicator that you have used to show the data fetch process is not used properly.
You data fetch process is still working, even after the activity indicator disappears.
You can do 2 things for that:
ether call the data fetch method in background using performSelectorInBackground method or place the activity indicator in the app delegate where you have created your data fetch method.