swift - 在解析中从用户获取对象

Question

在 Collection View 中，我有一个事件数组，每个单元格都有一个事件图像的背景 ImageView ，该图像保存为 PFFile。在我添加这段代码之前，它工作得很好。用户有一个属性“profilePicture”，我也想在单元格中显示它。这是我的代码，位于获取事件图像的 block 内部。

let eventCreator : PFUser = event?.objectForKey("user") as! PFUser
let creatorImage : PFFile = eventCreator.objectForKey("profilePicture") as! PFFile
creatorImage.getDataInBackgroundWithBlock({ (data, error) -> Void in

    cell.creatorImageView.image = UIImage(data: data!)

})

这是获取事件及其所有属性的完整方法(就像我所说的，在添加上述代码之前工作得很好。现在它抛出一个“ fatal error :在展开可选值时意外发现 nil”错误.有什么帮助吗？

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

    //sets up cell

    let cell : EventCell = collectionView.dequeueReusableCellWithReuseIdentifier("cell", forIndexPath: indexPath) as! EventCell

    //adds attend action

    cell.attendButton.addTarget(self, action: "buttonTapped:", forControlEvents: UIControlEvents.TouchUpInside)

    //queries parse for events

    let event = events?[indexPath.row]

    event?.eventImage.getDataInBackgroundWithBlock({ (data, error) -> Void in

        if let data = data, image = UIImage(data: data) {

            if cell.isFlipped == false {

            cell.eventBackgroundImage.image = image
            cell.eventTitleLabel.text = event?.eventTitle

            //gets profile picture of events creator

            let eventCreator : PFUser = event?.objectForKey("user") as! PFUser
            let creatorImage : PFFile = eventCreator.objectForKey("profilePicture") as! PFFile
            creatorImage.getDataInBackgroundWithBlock({ (data, error) -> Void in

                cell.creatorImageView.image = UIImage(data: data!)

            })

            //sets correct category for cell image

                if event?.category == "" {
                    cell.categoryImageView.image = nil
                }

                if event?.category == "The Arts" {
                    cell.categoryImageView.image = UIImage(named: "University")
                }

                if event?.category == "The Outdoors" {
                    cell.categoryImageView.image = UIImage(named: "Landscape")
                }

                //TODO finish categories

            }

            else if cell.isFlipped == true {

                cell.eventDescriptionLabel.text = event?.eventDescription
            }
        }
    })

Answer 1

强制将零值可选变量转换为非可选变量将导致运行时错误。为什么使用 as! 运算符？您可能应该使用 as? 运算符，并检查是否有任何 nil 值，以确保在执行任何操作之前强制转换成功。

[编辑]尝试这样的事情:

if let eventCreator = event?.objectForKey("user") as? PFUser {
    if let creatorImage = eventCreator.objectForKey("profilePicture") as? PFFile {
        creatorImage.getDataInBackgroundWithBlock({ (data, error) -> Void in

            cell.creatorImageView.image = UIImage(data: data!)

        })
    }
}