ios - 在 uicollectionview 中延迟加载

Question

这是我的 collectionview 的代码，它显示记录但确实加载请告诉我如何实现延迟加载我的项目中还有一个占位符图片

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

// Setup image name
    NSString *url = [[rssOutputData objectAtIndex:indexPath.row]xmllink];
    UIImage *img = nil;
    NSData *data = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]];
    img = [[UIImage alloc] initWithData:data];

    cell.MJImageView.image = img;
    return cell;
}

现在它正在运行，但非常非常慢。

Answer 1

使用 GCD 进行延迟加载非常容易。

    // Create a queue for the operations
    dispatch_queue_t queue = dispatch_queue_create("photoList", NULL);

    // Start getting the data in the background
    dispatch_async(queue, ^{
        NSData* photoData = [NSData dataWithContentsOfURL:[NSURL URLWithString:object.photoURL]];
        UIImage* image = [UIImage imageWithData:photoData];

        // Once we get the data, update the UI on the main thread
        dispatch_sync(dispatch_get_main_queue(), ^{
           cell.photoImageView.image = image;
        });
    });