Slow UITableView with Facebook Image - iphone

Question

I have a uitableview and each cells have an image from facebook image profile and 2 uilabels (from singleton, not an internet request)
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath*)indexPath
{
static NSString *CellIdentifier = #"MenuCell";
MenuCellViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
if (cell == nil) {
cell = [[MenuCellViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
//Singleton
DataModel *m = [DataModel getModel];
switch ([indexPath section]) {
case 0: //Only Header
break;
case 1: //My cells
{
//If footer - set footer background
if (indexPath.row == [tableView numberOfRowsInSection:indexPath.section] - 1){
[cell setBackgroundView:[[UIImageView alloc]initWithImage:[UIImage imageNamed:#"imgFooter.png"]]];
//Else - set normal cell background
} else {
[cell setBackgroundView:[[UIImageView alloc]initWithImage:[UIImage imageNamed:#"img.png"]]];
}
//Get Facebook image
strForImg = [[NSString alloc] initWithFormat:#"https://graph.facebook.com/%#/picture?type=square",[[[m list] objectAtIndex:indexPath.row] objectForKey:#"id"]];
url =[NSURL URLWithString:strForImg];
img = [UIImage imageWithData: [NSData dataWithContentsOfURL:url]];
[cell.imgProfile setImage:img];
//Set some text (uilabels)
cell.lblNom.text = [[[m list] objectAtIndex:indexPath.row] objectForKey:#"name"];
cell.lblTour.text = [[[m list] objectAtIndex:indexPath.row] objectForKey:#"description"];
break;
}
}
}
This code is very slow and freezes the tableview as it loads from facebook the profile images of each cell dynamically.
I tried doing with a dispatch like this
case 1://My cells
{
if (indexPath.row == [tableView numberOfRowsInSection:indexPath.section] - 1){
[cell setBackgroundView:[[UIImageView alloc]initWithImage:[UIImage imageNamed:#"imgFooter.png"]]];
} else {
[cell setBackgroundView:[[UIImageView alloc]initWithImage:[UIImage imageNamed:#"img.png"]]];
}
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
dispatch_sync(dispatch_get_main_queue(), ^{
strForImg = [[NSString alloc] initWithFormat:#"https://graph.facebook.com/%#/picture?type=square",[[list objectAtIndex:indexPath.row] objectForKey:#"id"]];
url =[NSURL URLWithString:strForImg];
img = [UIImage imageWithData: [NSData dataWithContentsOfURL:url]];
[cell.imgProfile setImage:img];
});
});
cell.lblNom.text = [[[m list] objectAtIndex:indexPath.row] objectForKey:#"name"];
cell.lblTour.text = [[[m list] objectAtIndex:indexPath.row] objectForKey:#"description"];
break;
}
The speed has slighty increased but it is still FREEZING when scrolling.
Is my dispatch not correct ? (I have just discovered it, maybe it is not well used).
Or is there any better method ?
I like the facebook friend picker. It puts a default profile image and refreshes the correct image profile when it is received from internet. How is this magic done ? :)

Answer 1

Fix this block:
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
strForImg = [[NSString alloc] initWithFormat:#"https://graph.facebook.com/%#/picture?type=square",[[list objectAtIndex:indexPath.row] objectForKey:#"id"]];
url =[NSURL URLWithString:strForImg];
img = [UIImage imageWithData: [NSData dataWithContentsOfURL:url]];
dispatch_sync(dispatch_get_main_queue(), ^{
[cell.imgProfile setImage:img];
});
});