ios - UICollectionView didDeselectItemAtIndexPath 影响多个单元格并给出 "nil"

Question

我有一个包含 11 个单元格的水平 Collection View ，当选择一个单元格时，其边框会变为绿色。我遇到的问题是，当我选择单元格时，它会更改不可见单元格的边框。

此外，当我选择最后一个单元格时，应用程序崩溃，给出“ fatal error :展开可选值时意外发现 nil”，引用 didDeselectItemAtIndexPath。

可能是什么问题？

func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return frameArray.count
    }

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

        let frameCell = collectionView.dequeueReusableCellWithReuseIdentifier("frameCell", forIndexPath: indexPath) as! FrameViewCell

        dispatch_async(dispatch_get_main_queue()) {
            frameCell.imageView.image = UIImage(named: self.frameArray[indexPath.row])
        }

        return frameCell
    }

    func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {

        dispatch_async(dispatch_get_main_queue()) {
            let frameCell = collectionView.cellForItemAtIndexPath(indexPath) as! FrameViewCell

            frameCell.layer.borderWidth = 2
            frameCell.layer.borderColor = UIColor.greenColor().CGColor
            frameCell.imageView.alpha = 1.0

            self.globalFrameIndex = self.frameArray[indexPath.row]
            self.framesImageViews(self.globalFrameIndex, image: self.globalImage)


            print(self.frameArray[indexPath.row])
        }
    }

    func collectionView(collectionView: UICollectionView, didDeselectItemAtIndexPath indexPath: NSIndexPath) {

        dispatch_async(dispatch_get_main_queue()) {
            let frameCell = collectionView.cellForItemAtIndexPath(indexPath) as! FrameViewCell

            frameCell.layer.borderWidth = 1
            frameCell.layer.borderColor = UIColor.whiteColor().CGColor
            frameCell.imageView.alpha = 0.5
        }

    }

}

Answer 1

更改您的函数以执行一些 if-let 可选检查:

func collectionView(collectionView: UICollectionView, didDeselectItemAtIndexPath indexPath: NSIndexPath) {

    dispatch_async(dispatch_get_main_queue()) {
        if let frameCell = collectionView.cellForItemAtIndexPath(indexPath) as? FrameViewCell
        {
            frameCell.layer.borderWidth = 1
            frameCell.layer.borderColor = UIColor.whiteColor().CGColor
            frameCell.imageView.alpha = 0.5
        } 
    }
}

更多信息可见in this related question .