Scroll view is not smooth - ios

Question

I'm working in a project (iOS7 & ARC) in which, I want to display N number of images in the scroll view.These Images already stored into sandbox directory. My App has only landscape orientation I'm facing a problem that ScrollView is not smooth, it stuck after 2-3 times scroll
This is how I configure ScrollView
[self.containerScroll setAutoresizesSubviews:NO];
self.containerScroll.pagingEnabled = YES;
self.containerScroll.showsHorizontalScrollIndicator = NO;
self.containerScroll.showsVerticalScrollIndicator = NO;
self.containerScroll.scrollsToTop = NO;
self.containerScroll.maximumZoomScale = 5.0;
self.containerScroll.minimumZoomScale = 1.0;
self.containerScroll.delegate = self;
I'm maintaining only three Images in the scrollView at a time.
I'm loading Images in ScrollView in below method
-(void) loadScrollViewWithPage:(int) page{
if (page >= self.numberOfSlides)
return;
float image_width;
float image_height;
if(self.isFromListView){
if(IS_IPHONE5){
image_width = 568.0f;
image_height = 320.0f;
} else{
// iPhone retina-3.5 inch
image_width = 480.0f;
image_height = 320.0f;
}
}
else{
image_width = IMAGE_WIDTH;
image_height = IMAGE_HEIGHT;
}
CGFloat xPos = page * image_width;
UIImageView *imgView = [[UIImageView alloc] initWithFrame:CGRectMake(xPos, 0.0f, image_width, image_height)];
imgView.tag = page;
NSString *imgPath = [self.storageDirPath stringByAppendingPathComponent:[NSString stringWithFormat:#"%d%#", page, Image_Extension_JPG]];
NSFileManager *fileManager = [NSFileManager defaultManager];
__block UIImage *img = nil;
if(![fileManager fileExistsAtPath:imgPath]){
[imgView setContentMode:UIViewContentModeCenter];
img = [UIImage imageNamed:#"icon-loader.png"];
[imgView setImage:img];
}
else{
[imgView setContentMode:UIViewContentModeScaleAspectFit];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
img = [[UIImage alloc] initWithCGImage:[[UIImage imageWithData:[NSData dataWithContentsOfFile:imgPath]] CGImage] scale:1.0 orientation:UIImageOrientationUp];
dispatch_async(dispatch_get_main_queue(), ^{
[imgView setImage:img];
});
});
}
[self.containerScroll addSubview:imgView];
img = nil;
fileManager = nil;
imgView = nil;
}
and this how my ScrollView Delegate methods goes...
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
self.containerScroll.scrollEnabled = YES;
float page = self.containerScroll.contentOffset.x/self.view.frame.size.width;
showingSlide = (UInt16) roundf(page);
if(scrollView == self.containerScroll){
// switch the indicator when more than 50% of the previous/next page is visible
CGFloat pageWidth = CGRectGetWidth(self.containerScroll.frame);
NSUInteger pageNo = floor((self.containerScroll.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
// load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
[self loadScrollViewWithPage:pageNo - 1];
[self loadScrollViewWithPage:pageNo];
[self loadScrollViewWithPage:pageNo + 1];
// a possible optimization would be to unload the views+controllers which are no longer visible
if(scrollView == self.containerScroll)
{
[self.previewTableView reloadData];
[self.previewTableView setContentOffset:CGPointMake(0, (page*220)+64) animated:NO];
[self.previewTableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:page inSection:0] atScrollPosition:UITableViewScrollPositionMiddle animated:YES];
[self updateSlideNumber];
[self flashSlideNumber];
}
//unload unnecessary imageviews from scroll view
for (UIView* view in self.containerScroll.subviews) {
if ([view isKindOfClass:[UIImageView class]] && view.tag != page && view.tag != page-1 && view.tag != page+1) {
[view removeFromSuperview];
}
}
}
}
Now the problem is smoothness of scrollView. When I start scrolling it scrolls fine but after 2 or 3 (or after any random number) pages scroll, it stuck and after trying 2-3 times only it moves again and I have to swipe hard to scroll. Thanks in advance.

Answer 1

I think it's a problem of memory somewhere Try #autorelease pool in your code.

Answer 2

using scrollview is not a good approach for showing images, I will recommend you to either use tableview or collevtionview for the same.
Your app's memory will keep on increasing with every scroll because scollview doesn't reuse the memory, on the other hand tableview and collectionview reuses the memory.

Answer 3

As the most effective way to become better, scroll really slowly (one at a time) while you monitor the memory usage in your App. You'll be able to watch it go up as each new image is added to the view, especially if you haven't done any optimisation on the images.
The other thing is that while your code does look like is deallocc-ing the images, you still need to remember that it still has to try to reload the images as you scroll. You're creating your images on the main thread so you're never going to get the smoothness of a UITableView. While I realise that you're creating your image views on async threads, the act of adding and scrolling them is still being taken care of by the mainthread.
I would suggest a UITableView to solve your problem, or a UICollectionView. If you're set on using the scrollview, I would suggest using a crusher of some type to get the image size to as small as possible, while still keeping quality decent.
If you need help on the TableView implementation you should find plenty of information around SO. Probably a good option if you still want it to look like a scroll view is just to make all seperators, headers etc to nil, and then just use lazy loading for the images.

Answer 4

You make two the mistake. At first: never use imageNamed for non graphics content (example, use imageNamed for button background). And second: you try load a big images in real time. So you scroll view have lags therefore. If you load all images before you show the scroll view the amination end lagging. But you can get memory warnings. So, you need optimise it. P.S. Sorry for my english