UITableView thumbnail image performance - ios

Question

My image data is being loaded from core data into a UITableView cell. These images are automatically scaled by the OS (as far as I know) in cellForRowAtIndexPath:indexPath:. Not surprisingly, this causes a lot of lag while scrolling through the table view.
Similarly, I have a UICollectionViewController that loads all the same images into a collection view similar to the iOS Photos app and again, the images are scaled in cellForItemAtIndexPath:indexPath. Scrolling is laggy, but it also takes a very long time for the VC to load.
What is the best way to optimize performance in this scenario?
I've done some research and have come up with a couple possible solutions:
Initialize a "thumbnailArray" in viewDidLoad:animated:, scaling all the images I need before the table/collection view is loaded, then use this new array as the data source for the views. I figure this will solve the scrolling issue, but not the collection view loading issue.
Create new properties for thumbnail data in my image wrapper class. This data would be created when the image wrapper object is created (i.e. when the user adds an image) and saved in core data. I think this would be preferred over option #1.
Is option two the best way to go, or is there a better solution I am unaware of?
Here are my cellForRowAtIndexPath:indexPath and cellForItemAtIndexPath:indexPath: methods:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
CMAEntryTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"entriesCell" forIndexPath:indexPath];
CMAEntry *entry = [self.entries objectAtIndex:indexPath.item];
cell.speciesLabel.text = [entry.fishSpecies name];
cell.dateLabel.text = [self.dateFormatter stringFromDate:entry.date];
if (entry.location)
cell.locationLabel.text = [entry locationAsString];
else
cell.locationLabel.text = #"No Location";
if ([entry.images count] > 0)
cell.thumbImage.image = [[entry.images objectAtIndex:0] dataAsUIImage];
else
cell.thumbImage.image = [UIImage imageNamed:#"no_image.png"];
if (indexPath.item % 2 == 0)
[cell setBackgroundColor:CELL_COLOR_DARK];
else
[cell setBackgroundColor:CELL_COLOR_LIGHT];
return cell;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"thumbnailCell" forIndexPath:indexPath];
UIImageView *imageView = (UIImageView *)[cell viewWithTag:100];
[imageView setImage:[[self.imagesArray objectAtIndex:indexPath.item] dataAsUIImage]];
return cell;
}
Thanks in advance!
Cohen

Answer 1

Thanks for your input, guys, but this is the solution that worked really well for me. The only thing I don't like is that now I store an NSData instance of the full image, and two different sized thumbnail images in core data; however, that doesn't seem to be a problem.
What I did was add a couple attributes to my NSManagedObject subclass to store the thumbnail images. The thumbnail data is initialized when the image is selected by the user, then saved in core data along with the original image.
Then, I load the thumbnails into a collection asynchronously in the view controllers I need them.
Works great. Gets rid of all issues I was experiencing.

Answer 2

1 I think the best approach is to load images in a background thread so the tableview loads quickly.
2 Also you can use coredata feature of batchsize to load only necessary data.
3 Perhaps using some type of cache in memory for the images may help

Answer 3

In one of my project i faced same kind of issue and i solved it by using AsyncImageView for loading the thumbimage for my tableview cell.It will load the image asynchronously.
#property (nonatomic,strong)AsyncImageView * thumbImageView;
self.thumbImageView =[[AsyncImageView alloc] init];
cell.thumbImageView.imageURL =[NSURL fileURLWithPath:UrlString];