ios - UICollectionViewController - 展开可选值时意外发现 nil

Question

我正在尝试实现一个 Collection View Controller ，但严重失败...我如何摆脱这个展开错误？当我在 cellForRowAtIndexPath 函数中创建 collectionView 单元格时，会发生这种情况。

这是代码。

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

let cell = picturesCollectionView.dequeueReusableCellWithReuseIdentifier(PhotoBrowserCellIdentifier, forIndexPath: indexPath) as? PhotoBrowserCollectionViewCell

    if let photoObject = pictureObjects.objectAtIndex(indexPath.row) as? PictureElement {

        let title = photoObject.title ?? "" // if photoObject.title == nil, then we return an empty string

        let timeStampDateObject = NSDate(timeIntervalSince1970: NSTimeInterval(photoObject.timeStamp))
        let timeStampDateString = dateFormatter.stringFromDate(timeStampDateObject)

        let author = photoObject.author ?? ""

        let issueNumber = photoObject.issueNumber ?? ""
        let volumeNumber = photoObject.volumeNumber ?? ""

        let nodeID = photoObject.nodeID ?? 0

        let imageURL = photoObject.imageURL ?? ""

        cell!.request?.cancel()

        // Using image cache system to make sure the table view works even when rapidly scrolling down the screen.
        if let image = self.imageCache.objectForKey(imageURL) as? UIImage {

            cell!.imageView.image = image

        } else {

            cell!.imageView.image = nil
            cell!.request = Alamofire.request(.GET, imageURL).responseImage { response in
                if let image = response.result.value {
                    self.imageCache.setObject(response.result.value!, forKey: imageURL)
                    cell!.imageView.image = image

                } else {
                }
            }
        }
    } else {
}
    return cell!

}

此外，我已经尝试使用guard-let 语句，但它不起作用。这是:

        guard let cell = picturesCollectionView.dequeueReusableCellWithReuseIdentifier(PhotoBrowserCellIdentifier, forIndexPath: indexPath) as? PhotoBrowserCollectionViewCell else {

        print("cell could not be initialized as PhotoBrowserCollectionViewCell, hence it will be casted to another default UICollectionViewCell type")
        return collectionView.dequeueReusableCellWithReuseIdentifier(PhotoBrowserCellIdentifier, forIndexPath: indexPath)


    }

Answer 1

假设您正在使用 Storyboard...

1. 确保为 Storyboard 中的单元设置重用标识符，以匹配 PhotoBrowserCellIdentifier 的值。

2. 确保将 Storyboard 中的单元格的类设置为 PhotoBrowserCollectionViewCell。