ios - 从 URL 和 Cache 中一张一张地加载和显示图片

我正在使用 SDWebImage 库在带有页面控件的 ScrollView 中显示图像。

如何一张一张下载图片并显示。假设我有 4 个 URL:url1,url2,url3,url4 所以我想先显示 url1 然后...2,3,4..等等...2,3,4 应该在后台加载，直到不下载占位符图像显示在那里。

下面是我尝试的内部 for 循环代码，它完美吗？

        NSString* serverImgicon=<url here in a loop>;
dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),^{
            NSURL *url=[NSURL URLWithString: serverImgicon];
            //set your image on main thread.
            dispatch_async(dispatch_get_main_queue(),^{
                [img sd_setImageWithURL:url
                       placeholderImage:[UIImage imageNamed"placeholderImg"]];
            });
        });

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Best Answer-推荐答案

试试下面的代码，它会正常工作的

 -(UICollectionViewCell *)collectionViewUICollectionView *)collectionView cellForItemAtIndexPathNSIndexPath *)indexPath{

        CollectionViewCell *cell =[collectionView dequeueReusableCellWithReuseIdentifier"cell" forIndexPath:indexPath];

        myobject *newobject = _myarray[indexPath.item];
        cell.nameLabel.text =newobject.name;

          dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
        dispatch_async(queue, ^{

            [cell.activityIndicatorForImage startAnimating];
            UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:
                                                     [NSURL URLWithString:newobject.image]]];
            dispatch_sync(dispatch_get_main_queue(), ^{
                if(image!= nil){
                    [[cell myimage] setImage:image];
                    [cell.activityIndicatorForImage setHidden:NO];

                }else{
                    UIImage * image = [UIImage imageNamed"LACEHOLDER"];
                    [[cell myimage] setImage:image];
                    [cell.activityIndicatorForImage setHidden:YES];
                    [cell.activityIndicatorForImage stopAnimating];

                }


                [cell setNeedsLayout];
            });
        });

        return cell;
    }

关于ios - 从 URL 和 Cache 中一张一张地加载和显示图片，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43840475/