使用GCD从设备加载UICollectionViewCell异步图像，

Question

I have a collection view that needs to display a collection of images whose files are saved on the device. They are all 600x600 pixels so I thought it would be better to create the UIImage asynchronously on a background thread and then set the image property of my UIImageView on the main thread. Below is where I do this in my (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath method

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{

        NSString *imageName = [NSString stringWithFormat:@"wo-%@", template.fileName];

        UIImage *image = [UIImage imageNamed:imageName];
        dispatch_async(dispatch_get_main_queue(), ^{
            if (image == nil)
            {
                self.collectionView.backgroundColor = [UIColor redColor];
                NSLog(@"image named: %@ in nil!", imageName);
            }
            cell.imageView.image = image;
        });
    });

    return cell;

Every once in a while image will be nil for one of the cells. It isn't reproducible and it's not always the same cell/image name. I was wondering if this has anything to do with using the UIImage imageNamed: method or am I using GCD incorrectly? Any thoughts on the issue would be appreciated.

Answer 1

For loading image asynchronously "SDWebImage" could be a best solution.

SDWebImage

just call the following method in your cellForItemAtIndexPath:

[cell.imageView sd_setImageWithURL:[NSURL URLWithString:@"http://www.example.com/path/to/image.jpg"]
         placeholderImage:[UIImage imageNamed:@"placeholder.png"]];