UICollectionView图像加载问题

Question

UICollectionView用于显示图像.它工作正常.

问题是当我滚动时UICollectionView,一些可见的单元格现在是不可见的,当我向后滚动以便它们再次可见时,我看到它们没有正确显示.

所以发生的imageA是在索引0并且imageB在索引1处.现在在滚动并且在再次加载这些单元格时返回原始滚动位置时,它们的位置被切换或者两个单元具有相同的图像.

原来 :

重新加载单元格后:

代码:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    MyCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"MyCell"
                                                                          forIndexPath:indexPath];

    DLog(@"url at index %d : %@", indexPath.row, ((MyObject *)[self.list.array objectAtIndex:indexPath.row]).imageUrl);

    MyObject *object = (MyObject *)[self.list.array objectAtIndex:indexPath.row];

    // Get image in separate thread
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // Get image to display
        UIImage * tempImage = object.image;

        if (tempImage)
        {
            // Run code to set image to UIImageView in main thread only.
            dispatch_async(dispatch_get_main_queue(), ^{

                cell.imageView.image = tempImage;
            });
        }
        else
        {
            // Download failed.
            DLog(@"Downloaded image is nil.");
        }
    });

    return cell;
}

我记录了图片网址的值,并记录了正确的值.

Answer 1

我也使用了这个技巧,但线程和线程之间的索引弄得一团糟,所以我搜索了一下,我在GitHub上找到了一个很棒的库.

• SDWebImage

您只需要进入#import <SDWebImage/UIImageView+WebCache.h>项目,并且只需使用以下代码即可在下载图像时定义占位符:

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    MyCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"MyCell"
                                                             forIndexPath:indexPath];

    DLog(@"url at index %d : %@", indexPath.row, ((MyObject *)[self.list.array objectAtIndex:indexPath.row]).imageUrl);

    MyObject *object = (MyObject *)[self.list.array objectAtIndex:indexPath.row];

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

    return cell;
}

它还可以缓存下载的图像并为您提供出色的性能.

希望它能帮到你!