Lag in UICollectionView on Scroll - ios

Question

I'm using UICollectionView for showing some images stored in NSMutableArray
Here is my code for cellForItemAtIndexPath
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
CollectionViewCell *cell = (CollectionViewCell*)[collectionView dequeueReusableCellWithReuseIdentifier:#"CollectionViewCell" forIndexPath:indexPath];
if (indexPath.row<self.bookMarksArray.count) {
cell.bookmarkImage.image = [self.bookMarksimages objectAtIndex:indexPath.row];
cell.bookmarkTitle.text =[self.bookMarkNames objectAtIndex:indexPath.row];
}else
{
UIImage *bookMarkImage=[UIImage imageNamed:#"emptyCell.png"];
cell.bookmarkImage.image = bookMarkImage;
cell.bookmarkTitle.text =#"";
}
cell.removeBtn.enabled = NO;
cell.delegate = self;
return cell;
}
I have maximum 32 items in array self.bookMarksImages,When i'm scrolling my collection view, i can notice that there is a lag on scroll (for only first time).
But when i replaced line cell.bookmarkImage.image = [self.bookMarksimages objectAtIndex:indexPath.row];
with a static image cell.bookmarkImage.image = [UIImage imageNamed:#"emptyCell.png"];
i can see there is no lag on scroll and my collection view is scrolling smoothly .
here is my code for bookmarkImage initialisation.
-(void)getAllBookmarkImages
{
self.bookMarksimages = [[NSMutableArray alloc] init];
self.bookMarkNames = [[NSMutableArray alloc] init];
NSArray *bookMarksArray = [BookMarks getBookMarks];
for (int i=0; i<self.bookMarksArray.count; i++) {
NSDictionary *bookmarkInfo = [bookMarksArray objectAtIndex:i];
UIImage *bookMarkImage=[UIImage imageWithContentsOfFile:[BookMarks documentsPathForFileName:[bookmarkInfo objectForKey:#"IMAGE"]]];
[self.bookMarksimages addObject:bookMarkImage];
[self.bookMarkNames addObject:[bookmarkInfo objectForKey:#"TITLE"]];
}
}
Why array self.bookMarksimages is causing lag?

Answer 1

There are many factors which is causing this issue
1.Image size
2.Image Location
A Workaround is load the image in async thread with help of image path.make a array of image path,instead image
- (void) loadImageFromPath:(NSString*)path{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, NULL), ^{
NSData *data= [NSData dataWithContentsOfFile:path];
UIImage *theImage=[UIImage imageWithData:data];
dispatch_async(dispatch_get_main_queue(), ^{
cell.bookmarkImage.imagee=theImage;
});
});
}
Usage
[cell loadImageFromFile:[self.bookMarksimages objectAtIndex:index]];