Image loading asynchronously, wrong image in cell

Question

I have UICollectionViewone in which I upload several images. From what I read to match the correct image in each cell, I need to subclass UIImageViewand get the image there. Since every time I collectionView reloadData, some images are duplicated, and they are all out of order. But I'm not sure how to do this and have not found any tutorials. I am using Parse for the database.

 - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
albumImageCell *cell = (albumImageCell *) [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];

     if (cell == nil) {
         cell = [[albumImageCell alloc]init];
     }

     PFObject *temp = [_dataArray objectAtIndex:indexPath.row];
     PFFile *file = [temp objectForKey:@"imageThumbnail"];

     if (![cell.hasImage isEqualToString:@"YES"]) {
         dispatch_async(imageQueue, ^{
             NSData *data = [file getData];
                 if (data) {
                     UIImage *image = [UIImage imageWithData:data];

                     dispatch_async(dispatch_get_main_queue(), ^(void){
                         cell.imageView.image = image;
                         cell.hasImage = @"YES";
                     });

                 }
         });
     }

     return cell;
}

Answer 1

What I ended up was subclassing UIImaveViewand then transferring the image file tocellForRow

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
albumImageCell *cell = (albumImageCell *) [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];

    if (cell == nil) {
        cell = [[albumImageCell alloc]init];
    }

    PFObject *temp = [_dataArray objectAtIndex:indexPath.row];
    PFFile *file = [temp objectForKey:@"imageThumbnail"];

    [cell.imageView setFile:file];

    return cell;
}  

---

And then at customImageView-

- (void) setFile:(PFFile *)file {

    NSString *requestURL = file.url; // Save copy of url locally (will not change in block)
    [self setUrl:file.url]; // Save copy of url on the instance
    self.image = nil;
    [file getDataInBackgroundWithBlock:^(NSData *data, NSError *error) {
        if (!error) {
            UIImage *image = [UIImage imageWithData:data];
            if ([requestURL isEqualToString:self.url]) {
                [self setImage:image];
                [self setNeedsDisplay];
            }
        } else {
            NSLog(@"Error on fetching file");
        }
    }];
}  

, . , , .

Answer 2

- , . :

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
albumImageCell *cell = (albumImageCell *) [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];

     if (cell == nil) {
         cell = [[albumImageCell alloc]init];
     }

     PFObject *temp = [_dataArray objectAtIndex:indexPath.row];
     PFFile *file = [temp objectForKey:@"imageThumbnail"];

     if (![cell.hasImage isEqualToString:@"YES"]) {
         dispatch_async(imageQueue, ^{
             NSData *data = [file getData];
                 if (data) {
                     UIImage *image = [UIImage imageWithData:data];

                     dispatch_async(dispatch_get_main_queue(), ^(void){
                         // cellAgain will be the actual cell at that index path, if it is visible. 
                         // If it is not visible, cellAgain will be nil.
                         albumImageCell *cellAgain = [collectionView cellForItemAtIndexPath:indexPath];
                         cellAgain.imageView.image = image;
                         cellAgain.hasImage = @"YES";
                     });

                 }
         });
     }

     return cell;
}

Answer 3

"" . , , .

, , - , . , , , , ( ), ...

(a) ?

if ([[tableView indexPathsForVisibleRows] containsObject:indexPath])

(b) , ?

 UITableViewCell * correctCell = [self.tableView cellForRowAtIndexPath:indexPath];

, - , . viewController , UIKit Core Data, viewController . , .