ios - warnBlockingOperationOnMainThread 错误

Question

我正在使用 parse 创建一个应用程序，我收到一条警告说 “正在主线程上执行长时间运行的 Parse 操作。中断 warnParseOperationOnMainThread() 进行调试。” 所以我有在 warnBlockingOperationOnMainThread 中放置一个断点。应用程序在断点处停止并指出 item.fetchIfNeeded。为什么会这样？我没有发现我的代码有任何问题。任何帮助表示赞赏。谢谢!

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

        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("loveView", forIndexPath: indexPath) as! LoveCollectionViewCell
        let item = self.votes[indexPath.row]


        let gesture = UITapGestureRecognizer(target: self, action: Selector("onDoubleTap:"))
        gesture.numberOfTapsRequired = 2
        cell.addGestureRecognizer(gesture)


        // Display "initial" flag image
        var initialThumbnail = UIImage(named: "question")
        cell.postsImageView.image = initialThumbnail

        // Display the country name
        if let user = item["uploader"] as? PFUser{
            item.fetchIfNeeded()
            cell.userName!.text = user.username


            var profileImgFile = user["profilePicture"] as! PFFile
            cell.profileImageView.file = profileImgFile
            cell.profileImageView.loadInBackground { image, error in
                if error == nil {
                    cell.profileImageView.image = image
                }
            }

            var sexInt = user["sex"] as? Int
            var sex: NSString!
            if sexInt == 0 {
                sex = "M"
            }else if sexInt == 1{
                sex = "F"
            }else{
                sex = " "
            }

            var height = user["height"] as? Int
            if height == nil{
                cell.heightSexLabel.text = " "
            }else{
                var nonOpHeight = height as Int!
                cell.heightSexLabel.text = "\(sex) \(nonOpHeight)cm"
            }


        }

        if let votesValue = item["votes"] as? Int
        {
            cell.votesLabel?.text = "\(votesValue)"
        }

        // Fetch final flag image - if it exists
        if let value = item["imageFile"] as? PFFile {
            println("Value \(value)")
            cell.postsImageView.file = value
            cell.postsImageView.loadInBackground({ (image: UIImage?, error: NSError?) -> Void in
                if error != nil {
                    cell.postsImageView.image = image
                }
            })
        }

        //Adjusting the position of heart image
        cell.votesLabel!.sizeToFit()
        cell.votesLabel!.center = CGPointMake(cell.bottomBlurView.center.x - (cell.heartImage.frame.width / 2)-1.5, cell.bottomBlurView.frame.size.height / 2)
        cell.heartImage.frame.origin.x = cell.votesLabel!.frame.origin.x + cell.votesLabel!.frame.width + 1.5



        return cell
    }

Answer 1

因为 fetcIfneeded 方法会在主线程执行，所以使用 fetchIfNeededInBackgroundWithBlock 方法代替。在 block 内部检查 success = true 然后获取文件。