async image table view xcode, but - objective-c

Question

I am using asynchronous loading of images in a cell.
My code is:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *const ImageCellId = #"ImageCell";
PDATableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ImageCellId];
if (cell == nil) {
cell = [[PDATableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:ImageCellId];
}
Tutorial *thisTutorial = [_objects objectAtIndex:indexPath.row];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSURL *tutorialsUrl8 = [NSURL URLWithString:thisTutorial.url]];
NSData *tutorialsHtmlData2 = [NSData dataWithContentsOfURL:tutorialsUrl8];
TFHpple *tutorialsParser2 = [TFHpple hppleWithHTMLData:tutorialsHtmlData2];
NSString *tutorialsXpathQueryString2 = #"//div[#class='photo']/img";
NSArray *tutorialsNodes2 = [tutorialsParser2 searchWithXPathQuery:tutorialsXpathQueryString2];
for (TFHppleElement *element2 in tutorialsNodes2) {
tutorial2 = [[Tutorial alloc] init];
tutorial2.url = [element2 objectForKey:#"src"];
data2 = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:tutorial2.url]];
}
if(data2)
{
imageMain = [UIImage imageWithData:data2];
if (imageMain) {
dispatch_async(dispatch_get_main_queue(), ^{
if (cell)
cell.cellImageView.image = imageMain;
});
}
}
});
return cell;
}
It works! But! When I scroll my TebleView, I have images loaded again.
What am I doing wrong?

Answer 1

You are loading the images asynchronously. Thats fine but you are not applying any caching mechanism.
By caching mechanism i mean a way which checks whether the image is already downloaded or not. If downloaded once then it should not download the image again instead use the already downloaded image.
These downloaded images should be saved locally so that they can be used every time the app is active. Its easy to implement this image caching mechanism but its better to use already existing api's which are much improved and optimized.
SDWebImage is the most optimized way of loading images asynchronously.
You can use SDwebImage, downloads the images and keeps them in cache memory (to speed up) and saves images locally.
Also in order to know other caching apis you can check this. I will always prefer SDWebImage as its really good and fast. link.
Hope this will help you. Happy coding :)