Xcode table view lag when scrolling - ios

Question

(void)bilgileriYukle
{
NSMutableArray *yemekIsimleri = [[NSMutableArray alloc] init];
NSMutableArray *resimIsimleri = [[NSMutableArray alloc] init];
NSURL *myURL = [[NSURL alloc]initWithString:#"http://www.sevgilezzeti.com/WebServices/tarifler.php"];
NSData *myData = [[NSData alloc]initWithContentsOfURL:myURL];
if (myData == nil)
{
NSLog(#"INTERNET YOK YADA VERI CEKEMEDI");
}
else
{
NSLog(#"INTERNET VAR VERI CEKILDI");
NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData:myData options:kNilOptions error:nil];
for (id element in jsonArray)
{
NSString *durum = [element objectForKey:#"durum"];
if([durum isEqualToString:#"1"])
{
[yemekIsimleri addObject:[element objectForKey:#"yemekadi"]];
NSString *gelenYemekAdi =[element objectForKey:#"kapakresmi"];
NSString *imagePathKapak = #"http://sevgilezzeti.com/Admin/yemekresimkapak/";
combined = [NSString stringWithFormat:#"%#%#", imagePathKapak, gelenYemekAdi];
[resimIsimleri addObject:combined];
}
}
}
_TarifAdi=yemekIsimleri;
_ResimAdi=resimIsimleri;
}
///////////////////////////////////////////////////////////////////////////////////////
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
TableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"TableViewCell" forIndexPath:indexPath];
NSUInteger row = [indexPath row];
cell.TitleLabel.text = _TarifAdi[row];
NSCache *_imageCache;
UIImage *image = [_imageCache objectForKey:#"DenemeRes"];
if (image == nil) {
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:_ResimAdi[row]]];
image = [UIImage imageWithData:data];
[_imageCache setObject:image forKey:#"DenemeRes"];
}
cell.ThumbImage.image = image;
return cell;
}
I can get images from URL and can see images but when I scroll the table view, it's very slow and lagging. How can I fix this problem ?

Answer 1

It's pretty easy and straightforward to load images synchronously in table view cells, however it's evil, because it would cause the lag when you scroll it, because it's actually trying to load and display the images as you're scrolling.
Therefore, you must avoid loading images synchronously, but asynchronously instead, using a different thread other than the main thread, so that the scrolling and loading + displaying images can be done dependently, avoiding any kind of lag.
This is possibly a duplicate question, since it's already been asked and there are tutorials out there, but since I myself always had a problem with this on my first iOS app and found it very confusing, I'm posting the answer here, hoping it's helpful.
Try adding something like this to your - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath:
// Get the filename to load.
NSString *imageFilename = [imageArray objectAtIndex:[indexPath row]];
NSString *imagePath = [imageFolder stringByAppendingPathComponent:imageFilename];
[[cell textLabel] setText:imageFilename];
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
UIImage *image = [UIImage imageWithContentsOfFile:imagePath];
dispatch_sync(dispatch_get_main_queue(), ^{
[[cell imageView] setImage:image];
[cell setNeedsLayout];
});
});

Answer 2

dataWithContentsOfURL is blocking your main thread, that'w why the table is acting like it is. You should load images in back thread so that the main thread can handle UI without interruptions
NSURL *url = [NSURL URLWithString:link];
NSURLRequest *urlRequest = [[NSURLRequest alloc] initWithURL:url cachePolicy:0 timeoutInterval:kTimeoutInterval];
[NSURLConnection sendAsynchronousRequest:urlRequest
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
UIImage *image = [[UIImage alloc] initWithData:self.activeDownload];
// set to ImageView
cell.ThumbImage.image = image;
}];

Answer 3

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
TableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"TableViewCell" forIndexPath:indexPath];
cell.tag = indexPath.row;
cell.imageView.image = nil;
// Rounded Rect for cell image
CALayer *cellImageLayer = cell.imageView.layer;
[cellImageLayer setCornerRadius:35];
[cellImageLayer setMasksToBounds:YES];
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_async(queue, ^(void) {
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:_ResimAdi[indexPath.row]]];
UIImage *image = [[UIImage alloc] initWithData:data];
if (image) {
dispatch_async(dispatch_get_main_queue(), ^{
if (cell.tag == indexPath.row) {
CGSize itemSize = CGSizeMake(70, 70);
UIGraphicsBeginImageContext(itemSize);
CGRect imageRect = CGRectMake(0.0, 0.0, itemSize.width, itemSize.height);
[image drawInRect:imageRect];
cell.imageView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[cell setNeedsLayout];
}
});
}
});
cell.TitleLabel.text = _TarifAdi[indexPath.row];
return cell;
}