UITableViewCell Data load error - objective-c

Question

I am parsing some images and strings from a JSON file, the parsing works fine, but the image loading is very slow. I notized, the UITableView shows the content quicker, when I press on the UITableViewCell. Does anyone know a fix for that?
Here is the code I use, I use a NSOperationQueue to keep the CPU usage low.
NSDictionary *dict;
dict = [application objectAtIndex:indexPath.row];
name = [dict objectForKey:#"name"];
detileName = [dict objectForKey:#"detailName"];
itmsLink = [dict objectForKey:#"itms-serviceLink"];
icon = [dict objectForKey:#"icon"];
developer = [dict objectForKey:#"developer"];
version = [dict objectForKey:#"version"];
category = [dict objectForKey:#"category"];
rating = [dict objectForKey:#"rating"];
ratingNumbers = [dict objectForKey:#"ratingNumber"];
description = [dict objectForKey:#"description"];
developerEmails = [dict objectForKey:#"developerEmail"];
[downloadQueue addOperationWithBlock:^{
cell.AppName.text = name;
cell.category.text = category;
cell.rater.text = [NSString stringWithFormat:#"(%#)", ratingNumbers];
if ([rating intValue] == 1) {
cell.rating.image = [UIImage imageNamed:#"1.png"];
}
if ([rating intValue] == 2) {
cell.rating.image = [UIImage imageNamed:#"2.png"];
}
if ([rating intValue] == 3) {
cell.rating.image = [UIImage imageNamed:#"3.png"];
}
if ([rating intValue] == 4) {
cell.rating.image = [UIImage imageNamed:#"4.png"];
}
cell.itms = itmsLink;
cell.AppIcon.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:icon]]];
cell.number.text = [NSString stringWithFormat:#"%li", (long)indexPath.row + 1];
}];

Answer 1

It looks like you've already got most of the data you need to present the cell, except for image that will go in AppIcon.image. the way things are set up now, the image download is blocking you from presenting the cell immediately. my guess is that the image download does eventually complete, but you do not force the cell to redraw itself after the download has finished. tapping on a cell forces it to redraw itself, which is probably why you're seeing the behavior you described.
I suggest you present the cell immediately using the data that you already have downloaded, and kick off a background download of the image. When the download is complete, you can send an NSNotification and update the appropriate cell. you can do this by creating a subclass of NSOperation that accepts a URL during initialization, and then adding that op to your operation queue
if you don't want to do all that work yourself, there is a category on UIImageView that uses AFNetworking to do the update for you using blocks.
https://github.com/zbowling/AFNetworkingPollTest/blob/master/ServerTest/UIImageView%2BAFNetworking.h

Answer 2

As stated by #Nick Galasso - you don't refresh the cell's and passing the cell pointer to a block is a very bad practice since UITableView actually reuses the cell's and when download is complete you should obtain cell pointer again - you are interested in cell under actual NSIndexPath, not the object.
Under a link:
https://developer.apple.com/library/ios/samplecode/LazyTableImages/Introduction/Intro.html
You can find perfect sample code on lazy image loading, fragment below shows the part which actually brings the view, this code called on download finish set's the image asap:
UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
cell.imageView.image = downloadedImage;
You can call it in some completion handler of downloading class (the sample under Apple link covers that).