LazyTableImages

 

官方demo http://download.csdn.net/detail/jlyidianyuan/5726749

在tableView：cellForRowAtIndexPath方法中

 // Only load cached images; defer new downloads until scrolling ends

　　　//图片是否存在

        if (!appRecord.appIcon)

        {

　　　　 //tableView是否在拖拽或减速

            if (self.tableView.dragging == NO && self.tableView.decelerating == NO)

            {

　　　　　 //开个线程或使用GCD异步下载图片 下载图片后可以将图片存在沙盒 此处不详情写出

                [self startIconDownload:appRecord forIndexPath:indexPath];

            }

            // if a download is deferred or in progress, return a placeholder image

　　　　 //放张默认的图片

            cell.imageView.image = [UIImage imageNamed:@"Placeholder.png"];                

        }

        else

        {

           cell.imageView.image = appRecord.appIcon;

        }

 

//实现UIScrollViewDelegate

#pragma mark -

#pragma mark Deferred image loading (UIScrollViewDelegate)

 

// Load images for all onscreen rows when scrolling is finished

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate

{

    if (!decelerate)

{

        [self loadImagesForOnscreenRows];

    }

}

 

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView

{

    [self loadImagesForOnscreenRows];

}

- (void)loadImagesForOnscreenRows

{

    if ([self.entries count] > 0)

    {

        NSArray *visiblePaths = [self.tableView indexPathsForVisibleRows];

        for (NSIndexPath *indexPath in visiblePaths)

        {

            AppRecord *appRecord = [self.entries objectAtIndex:indexPath.row];

            

            if (!appRecord.appIcon) // avoid the app icon download if the app already has an icon

            {

                [self startIconDownload:appRecord forIndexPath:indexPath];

            }

        }

    }

}