Large Images Crashing UITableView app - ios

Question

So I've been searching for an answer to this and still am unable to figure it out. I have an array that contains 15 images or so I'm trying to display using a subview in a UITableViewCell. Code below - everything I've read mentions using autorelease/release to fix the issue, but I simply get ARC errors when attempting to do that. Any help would be much appreciated.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
int countthis = indexPath.row;
NSString *image = imgarr[countthis];
UIImageView *iv = [[UIImageView alloc] initWithFrame:(CGRect){.size={320, tableView.rowHeight}}];
iv.image = [UIImage imageNamed:image];
cell.imageView.image = iv.image;
return cell;
}

Answer 1

Large files tend to cause problems, no matter what your domain. Specifically, Apple says:
You should avoid creating UIImage objects that are greater than 1024 x 1024 in size.
It looks like you're trying to resize the image, but UIImages are immutable. So your allocated UIImageView serves only to waste processor cycles.
If you're stuck with big images that need to be scaled down, consider scaling before you assign them to the cell. You might find these routines useful: The simplest way to resize an UIImage?
Re autorelease/release: those have been deprecated since ARC. Your code doesn't appear to be leaking memory. I wouldn't sweat it. But you should edit your question to include details about the crash.

Answer 2

Your code can be cleaned up to this, which may help slightly with performance. You don't need to convert the indexPath.row to an int, since it's already a NSInteger, which is an architecture dependent type (int for 32-bit, long for 64-bit). You also probably want to use self.imgarr since its probably a property in your class. The image changes are as Neal mentioned.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
NSString *image = self.imgarr[indexPath.row];
cell.imageView.image = [UIImage imageNamed:image];
return cell;
}
As for autorelease/release, you mentioned you're getting ARC errors using them, which indicates you're on the iOS 5 or higher SDK. They are no longer needed in your code.

Answer 3

You can try to resize images using CGImageSourceCreateThumbnailAtIndexfirst before displaying them in the tableview.
If you have the path to the image you want to resize, you can use this:
- (void)resizeImageAtPath:(NSString *)imagePath {
// Create the image source (from path)
CGImageSourceRef src = CGImageSourceCreateWithURL((__bridge CFURLRef) [NSURL fileURLWithPath:imagePath], NULL);
// To create image source from UIImage, use this
// NSData* pngData = UIImagePNGRepresentation(image);
// CGImageSourceRef src = CGImageSourceCreateWithData((CFDataRef)pngData, NULL);
// Create thumbnail options
CFDictionaryRef options = (__bridge CFDictionaryRef) #{
(id) kCGImageSourceCreateThumbnailWithTransform : #YES,
(id) kCGImageSourceCreateThumbnailFromImageAlways : #YES,
(id) kCGImageSourceThumbnailMaxPixelSize : #(640)
};
// Generate the thumbnail
CGImageRef thumbnail = CGImageSourceCreateThumbnailAtIndex(src, 0, options);
CFRelease(src);
// Write the thumbnail at path
CGImageWriteToFile(thumbnail, imagePath);
}
More details here.