Question

我在项目中设置了一个从JSON文件中获取数据的uicollectionview。然而，一切都运行良好，滚动非常慢，当视图滚动即将到来的单元格时，片刻之前会显示单元格的内容。

我尝试过使用dispatch_async，但它仍然很慢而且很跳跃。

任何想法我做错了什么？

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

        let videoCell = collectionView.dequeueReusableCellWithReuseIdentifier("VideoCell", forIndexPath: indexPath) as UICollectionViewCell
        let communityViewController = storyboard?.instantiateViewControllerWithIdentifier("community_id")

        videoCell.frame.size.width = (communityViewController?.view.frame.size.width)!
        videoCell.center.x = (communityViewController?.view.center.x)!

        videoCell.layer.borderColor = UIColor.lightGrayColor().CGColor
        videoCell.layer.borderWidth = 2


        let fileURL = NSURL(string:self.UserVideosInfo[indexPath.row][2])
        let asset = AVAsset(URL: fileURL!)
        let assetImgGenerate = AVAssetImageGenerator(asset: asset)
        assetImgGenerate.appliesPreferredTrackTransform = true
        let time = CMTimeMake(asset.duration.value / 3, asset.duration.timescale)

        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {

            //self.showIndicator()

            let NameLabelString = self.UserVideosInfo[indexPath.row][0]
            let CommentLabelString = self.UserVideosInfo[indexPath.row][1]
            let DateLabelString = self.UserVideosInfo[indexPath.row][3]

            let buttonPlayUserVideo = videoCell.viewWithTag(1) as! UIButton
            let nameLabel = videoCell.viewWithTag(2) as! UILabel
            let commentUserVideo = videoCell.viewWithTag(3) as! UILabel
            let dateUserVideo = videoCell.viewWithTag(4) as! UILabel
            let thumbUserVideo = videoCell.viewWithTag(5) as! UIImageView
            let deleteUserVideo = videoCell.viewWithTag(6) as! UIButton

            buttonPlayUserVideo.layer.setValue(indexPath.row, forKey: "indexPlayBtn")
            deleteUserVideo.layer.setValue(indexPath.row, forKey: "indexDeleteBtn")

            dispatch_async(dispatch_get_main_queue()) {



                nameLabel.text = NameLabelString
                commentUserVideo.text = CommentLabelString
                dateUserVideo.text = DateLabelString

                self.shadowText(nameLabel)
                self.shadowText(commentUserVideo)
                self.shadowText(dateUserVideo)

                if let cgImage = try? assetImgGenerate.copyCGImageAtTime(time, actualTime: nil) {
                    thumbUserVideo.image = UIImage(CGImage: cgImage)
                }


            }

        }

        //THIS IS VERY IMPORTANT
        videoCell.layer.shouldRasterize = true
        videoCell.layer.rasterizationScale = UIScreen.mainScreen().scale


        return videoCell
    }

Answer 1

起初 - 您正在使用全局队列中的UI对象，似乎没有任何意义。这是被禁止的 - 或者行为将是不确定的。

辅助，最重要的操作是创建您在主队列上执行的缩略图。考虑使用AVAssetImageGenerator方法

public func generateCGImagesAsynchronouslyForTimes(requestedTimes: [NSValue], completionHandler handler: AVAssetImageGeneratorCompletionHandler)

而不是你自己的asyncs。

第三次，viewWithTag操作非常繁重，导致subviews上的枚举。考虑在单元格中为您需要的视图声明属性。

UPD：要在单元格中声明属性，请创建具有适当属性的UICollectionViewCell的子类作为IBOutlets。然后，在您的视图控制器viewDidLoad实现中，调用

collecionView.registerClass(<YourCellSubclass>.dynamicType,  forCellWithReuseIdentifier:"VideoCell")

或者，如果在故事板中配置了集合视图单元格，请指定单元格的类并将其子视图连接到类＆＃39;直接在Interface Builder的单元格设置窗口中输出。

第四次，您的单元格正在被集合视图重用。每当您的单元格离开可见区域时，它将从集合视图中删除并放入重用队列。当您向后滚动到单元格时，会再次要求您的视图控制器提供单元格。并且您为每个新出现的单元格再次获取视频的缩略图。考虑通过collectionView的indexPath.item索引将已存取的缩略图存储在某个数组中来缓存这些缩略图。

SWIFT 2 - UICollectionView - 慢速滚动

1 个答案: