ios - Passing data from CollectionView to DetailVC in Swift 4

Question

My CollectionView should pass a class model to DetailViewController, but when I tap on a cell I get the nil error.

Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value

The CollectionViewController is embedded programmatically on a TabBarController.

Collection View

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

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "SoundCell", for: indexPath) as? SoundCell {
    let SoundClass = soundArray[indexPath.row]
    cell.updateUI(SoundClass: SoundClass)
    return cell

    } else {
    return UICollectionViewCell()
    }
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {

    self.performSegue(withIdentifier: "seguetosound", sender: self)

  }

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    if segue.identifier == "seguetosound" {
    if let detailVC = segue.destination as? DetailSecondVC
    let sound = sender as? SoundClass { 
    detailVC.SoundClass = sound 

    }
 }

Detail View Controller

class DetailSecondVC: UIViewController, UIWebViewDelegate {

private var _SoundClass: SoundClass!

var SoundClass: SoundClass {
        get {
            return _SoundClass
        } set {
            _SoundClass = newValue
        }
    }

Do you know what I am missing here? I tested the segue with a simple white screen and it works but when I try to pass the data, it fails.

Answer 1

The correct approach is this. First, figure out how you want to trigger the segue. One option is, in didSelect, trigger the segue in code:

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    self.performSegue(withIdentifier: "seguetosound", sender: self)
}

But even better, just delete didSelectItemAt completely and have the segue in the storyboard come from the cell. That way the segue is triggered automatically when the user taps the cell.

Then, in prepare, find out what index path was selected, and pull out the data from the model and pass it to the destination view controller (this might not compile, because your variable names are so atrocious that I can't read your code, but it is the correct approach generally):

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "DetailSecondVC" {
        if let detailVC = segue.destination as? DetailSecondVC {
            if let paths = collectionView?.indexPathsForSelectedItems {
                let row = paths[0].row
                detailVC.SoundClass = SoundClasss[row]
            }
        }
    }
}