Swift Collection查看不可重用的单元格

Question

I have a collectionView with 2 sections, each section should be based off the same cell (which only contains a UIImageView). The only difference between the sections is the number of cells they should contain and types of images displayed.

If I set the cellforItemAtIndexPath method to use a dequeued cell (collectionView.dequeueReusableCellWithIdentifier) everything populates fine, if I set it to use an instance of my custom cell without dequeuing, it crashes.

cellForItemAtIndexPath method:

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        //cannot use dequedReusableCell since some cells below scroll-line should remain highlighted
        let cell = NumbersCollectionViewCell() // CAUSES CRASH
//        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(Constants.cellIdentifier, forIndexPath: indexPath) as! NumbersCollectionViewCell // WORKS FINE
        switch indexPath.section {
        case 0: cell.imageView.image = UIImage(named: numberImageFiles[indexPath.row])
        case 1: cell.imageView.image = UIImage(named: specialNumberImageFiles[indexPath.row])
        default: break
        }
        return cell
    }

NumbersCollectionViewCell definition:

class NumbersCollectionViewCell: UICollectionViewCell {
    @IBOutlet weak var imageView: UIImageView!
}

The error that appears is: "Fatal error: unexpectedly found nil while unwrapping an Optional value" and it highlights the "case 0" row in my cellForItemAtIndexPath method.

The reason I don't want to use a dequeued cell is that I need some of the cells to be highlighted at run-time based on user selections, and if I use a dequeued cell it doesn't seem to keep the ones below the scroll-line highlighted.

Answer 1

Assuming that you have both a .swift and a .xib file for your cell, you need to instantiate your NumbersCollectionViewCell like this: Eg

let numbersCollectionViewCell = UINib(nibName: "NumbersCollectionViewCell", bundle: bundle).instantiateWithOwner(nil, options: nil)[0] as! NumbersCollectionViewCell

Otherwise, your IBOutlet s will not be connected.

Answer 2

 override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
     guard let cell = collectionView.dequeueReusableCellWithReuseIdentifier(identifier: "NumbersCollectionViewCell">, forIndexPath: NSIndexPath>) as? NumbersCollectionViewCell else {
         print("failed to get cell")
         return UICollectionViewCell()
         }
     switch indexPath.section {
         case 0: cell.imageView.image = UIImage(named: numberImageFiles[indexPath.row])
         case 1: cell.imageView.image = UIImage(named: specialNumberImageFiles[indexPath.row])
         default: break
         }
   return cell
}