如何异步加载CollectionView细胞图像？

Question

现在我有一个UICollectionView（水平滚动）哪些单元格包含UIImage。我使用这个功能来显示UIImage过滤器，就像Instagram一样。但是当我滚动查看实现过滤器后图像的外观时 - 它会冻结。我如何才能让它流畅如Instagram？

我的代码：

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell { 
    let cell: imageFilterCell = collectionView.dequeueReusableCellWithReuseIdentifier("cell", forIndexPath: indexPath) as! imageFilterCell 

    NSOperationQueue.mainQueue().addOperationWithBlock {    
     cell.imageView.image = self.applyFilterTo(self.image!, filter: self.filtersImages[indexPath.row]) 
     cell.imageView.layer.cornerRadius = 5 
     cell.imageView.layer.masksToBounds = true 
     cell.filterLabel.text = self.filtersLabels[indexPath.row] 
    } 

    return cell 
} 

其中applyFilter()实现了一个过滤器，我的形象。

任何解决方案使滚动平滑，并防止冻结？

Answer 1

试试这个

let queue = NSOperationQueue() 

     let op1 = NSBlockOperation {() -> Void in 

      let img1 = self.applyFilterTo(self.image!, filter: self.filtersImages[indexPath.row]) 

      NSOperationQueue.mainQueue().addOperationWithBlock({() -> Void in 
       cell.imageView.image = img1 
      }) 
     } 


queue.addOperation(op1); 
cell.imageView.layer.cornerRadius = 5 
     cell.imageView.layer.masksToBounds = true 
     cell.filterLabel.text = self.filtersLabels[indexPath.row] 

Answer 2

试试这个

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

     NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:parsedData[@"imageURL"]]; 

     UIImage* image = [[UIImage alloc] initWithData:imageData]; 
     if (image) { 
      dispatch_async(dispatch_get_main_queue(), ^{ 

        cell.imageView.image = image; 
        [cell setNeedsLayout]; 

      }); 
     } 
    });