我见过很多例子,但似乎没有最好的做法.例如,一个教程建议使用scrollViewDidScroll,但每次滚动视图时都会调用它.这是正确的实施吗？

PS.我在Swift编写代码.

这是我的细胞创建代码：

func collectionView(collectionView: UICollectionView!,cellForItemAtIndexPath indexPath: NSIndexPath!) -> UICollectionViewCell! {

    let cell = collectionView.dequeueReusableCellWithReuseIdentifier(cellIdentifier,forIndexPath: indexPath) as UICollectionViewCell

    let offer = self.offers[indexPath.row]
    var cellImageView = cell.viewWithTag(100) as UIImageView
    let requestURL = NSURLRequest(URL: offer.largeImageURL)
    cellImageView.setImageWithURLRequest(
        requestURL,placeholderImage:placeholderImage,success: {
            (request:NSURLRequest!,response:NSHTTPURLResponse!,image:UIImage!) in
            cellImageView.image = image
        },failure: {
            (request:NSURLRequest!,error:NSError!) in
            NSLog("GET Image Error: " + error.localizedDescription)
        }
    )
    return cell
}