UICollectionView didDeselectItemAtIndexPath 影響多個單元格並給出“nil”

Question

I have an horizo​​ntal collection view containing 11 cells when selecting a cell its border changes to green. 我遇到的問題是，當我選擇單元格時，它會更改不可見單元格的邊框。

此外，當我選擇最后一個單元格時，應用程序崩潰並給出“致命錯誤：在展開可選值時意外發現 nil”，指的是didDeselectItemAtIndexPath 。

可能是什么問題呢？

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

更改您的函數以進行一些 if-let 可選檢查：

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
        } 
    }
}

更多信息可以在這個相關問題中看到。