dequeueReusableCellWithIdentifier causing problem on UIImageView

I am loading a tableView with 500 rows. The problem is that in each row there is a different picture. Or when I use dequeueReusableCellWithI开发者_Python百科dentifier, those picture are just loaded again and the real pictures I am looking for are not shown (I just have about 8 different pictures : the first 8 loaded on my screen). If I don't use the dequeureReusableCellIdentifier, all the picture are loaded. But will it slow the displaying ?

Here is the code (I am currently working on getting the picture cached) :

- (UITableViewCell *)tableView:(UITableView *)tableView
         cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *CustomCellIdentifier = @"CustomCellIdentifier";
    UITableViewCell *cell = [tableView
                             dequeueReusableCellWithIdentifier: CustomCellIdentifier];

    NSLog(@"Launching CellForRowAtIndexPath");
    if (cell == nil) {
        NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"CustomCell"
                                                     owner:self options:nil];
        if ([nib count] > 0) {
            cell = self.profilCell;
        } else {
            NSLog(@"failed to load CustomCell nib file!");
        }
    }
    NSUInteger row = [indexPath row];
    NSDictionary *rowData = [listProfils objectAtIndex:row];
    UILabel *nameLabel = (UILabel *)[cell viewWithTag:nameValueTag];
    nameLabel.text = [rowData objectForKey:@"name"];
    NSString *finalId = [NSString stringWithFormat:@"http://graph.facebook.com/%@/picture", [rowData objectForKey:@"id"]];
    UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:finalId]]];
    [profilPic setImage:image];
    return cell;
}

THank you ! :)

---

It looks like you have an ivar profilPic that is probably an outlet that gets linked when you load a new cell nib. If that's the case, it's always going to point to the last cell that you loaded and won't change the image in the cell you've just dequeued. Instead of using an outlet, you might want to identify that custom view some other way, like a tag. So, if you set the profile pic UIImageView's tag to 100, for example, in Interface Builder, you could do something like this:

UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:finalId]]];
UIImageView* cellImageView = (UIImageView*)[cell viewWithTag:100];
[cellImageView setImage:image];

Also, I just want to point out that -dataWithContentsOfURL: will load the URL synchronously on the main thread. If you're testing in the simulator on a fast connection, this will work pretty well. If, however, you are on 3G in SoHo on Friday afternoon... your app will probably start being killed by the watchdog.

---

I just met this problem, my solution is hold a private NSMutableDictionary to store the new images which asynchronously loaded from web before, use my identifier as key, UIImageView as Object (because I need to load the icon image first), when web image is ready, change it, When tableView dequeue return's null, I can read the original UIImage from my own cache.

Something like this.

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
if (!cell) {
    UIImageView *imageView = [thumbnailCache objectForKey:identifier];
    if (!imageView) {
        cell.imageView.image = [UIImage imageNamed:@"icon.png"];
        [thumbnailCache setObject:cell.imageView forKey:identifier];
    } else {
        cell.imageView.image = imageView.image;
    }
}

When I load the actual image from web, refresh the thumbnail cache.

asynchronously_load_image_from_web(^(UIImage *image) {
    cell.imageView.image = image;
    [thumbnailCache setObject:cell.imageView forKey:identifier];
});