Objective C自定义延迟加载图像UITableView单元格

Question

首次将远程图像加载到iPhone应用程序中,并希望有一些帮助优化该过程.我目前所做的是获取图像(如果它不存在)并缓存它.主要目标是:

• 仅在需要时加载图像.
• 保存图像以备将来使用以减少数据消耗,并允许用户在未连接到互联网时拥有一个功能有点的应用程序.

我只是觉得我做得不够好.

这是tableView中的代码片段:cellForRowAtIndexPath:

MVImageCell * cell = (MVImageCell *)[tableView dequeueReusableCellWithIdentifier:@"PicsAndVideosCell"];

// empty cell
cell.imageView.image = nil;
cell.textLabel.text = nil;
cell.detailTextLabel.text = nil;

// set cell properties
cell.textLabel.lineBreakMode = UILineBreakModeWordWrap;
cell.textLabel.numberOfLines = 2;
cell.imageView.contentMode = UIViewContentModeScaleAspectFit;
cell.imageView.frame = CGRectMake(15, 6, 58, 58);
cell.imageView.layer.cornerRadius = 6;
cell.imageView.layer.masksToBounds = YES;

Photoset * sfc = [self.myarray objectAtIndex:indexPath.row];
cell.cid = sfc.sfcid;
cell.ctitle = sfc.title;
cell.cimg = sfc.cover;

cell.textLabel.text = sfc.title;
cell.detailTextLabel.text = sfc.date;

// set cell image
MVImage * thumb = [[MVImage alloc] init];
NSString * retina = ([[MVProject sharedInstance] settings_retina]) ? @"2" : @"";
if ([NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:[NSString stringWithFormat:@"Settings_SFCCovers%@_%@", retina, cell.cid]]]) {
    thumb = [NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:[NSString stringWithFormat:@"Settings_SFCCovers%@_%@", retina, cell.cid]]];

    [cell.imageView setImage:[MVImage imageWithImage:[[UIImage alloc] initWithData:thumb.data] covertToWidth:58.0f covertToHeight:58.0f]];
    [cell bringSubviewToFront:[cell.imageView superview]];
} else {
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
    dispatch_async(queue, ^{
        dispatch_sync(dispatch_get_main_queue(), ^{
            thumb.data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@", cell.cimg]]];
            thumb.title = cell.ctitle;
            [[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:thumb] forKey:[NSString stringWithFormat:@"Settings_SFCCovers%@_%@", retina, cell.cid]];

            [cell.imageView setImage:[MVImage imageWithImage:[[UIImage alloc] initWithData:thumb.data] covertToWidth:58.0f covertToHeight:58.0f]];
            [cell bringSubviewToFront:[cell.imageView superview]];
        });
    });
}

return cell;

我应该使用SQLite数据库而不是NSUserDefaults吗？

我也遇到了异步加载问题.我觉得它应该是这样的:

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
    thumb.data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@", cell.cimg]]];
    thumb.title = cell.ctitle;
    [[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:thumb] forKey:[NSString stringWithFormat:@"Settings_SFCCovers%@_%@", retina, cell.cid]];

    dispatch_sync(dispatch_get_main_queue(), ^{
        [cell.imageView setImage:[MVImage imageWithImage:[[UIImage alloc] initWithData:thumb.data] covertToWidth:58.0f covertToHeight:58.0f]];
        [cell bringSubviewToFront:[cell.imageView superview]];
    });
});

但这显然将错误的图像数据保存到NSUserDefault目的地.

任何有关这方面的帮助,关于我的编码风格的指针,以及其他任何内容都非常感谢.

谢谢!

Answer 1

只需快速查看代码 - 您似乎将块推送到异步队列,但您在这些块中调用UI代码.

您应该只在主线程上运行UI代码.

至于解决方案 - 看看一些开源实现,或者让你知道你应该做什么,或者直接使用它们.

其中一个是Github 上的AsyncImageView.

还有其他人会提出快速搜索.