GitHub - joywt/ImageLazyLoad: 列表图片加载优化

实例采用的动画效果是简单的渐显，如需修改动画效果可修改 ImageLazyLoadViewController.m文件中的 - (void)setupCell:(UITableViewCell *)cell cellForRowAtIndexPath:(NSIndexPath *)indexPath 方法，源代码如下：

```
if (cellImageView && targetURL && ![[cellImageView sd_imageURL] isEqual:targetURL]) {
    cellImageView.alpha = 0.0;
    SDWebImageManager *manager = [SDWebImageManager sharedManager];
    CGRect cellFrame = [self.tableView rectForRowAtIndexPath:indexPath];
    BOOL shouldLoadImage = YES;
    if (self.targetRect && !CGRectIntersectsRect([self.targetRect CGRectValue], cellFrame)) {
        SDImageCache *cache = [manager imageCache];
        NSString *key = [manager cacheKeyForURL:targetURL];
        if (![cache imageFromMemoryCacheForKey:key]) {
            shouldLoadImage = NO;
        }
    }
    
    if (shouldLoadImage) {
        [cellImageView sd_setImageWithURL:targetURL placeholderImage:self.defaultImage options:SDWebImageHandleCookies completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
            if ([imageURL isEqual:targetURL]) {
                [UIView animateWithDuration:0.3 animations:^{
                    cellImageView.alpha = 1.0;
                }];
            }
        }];
    }
    
}

```