如何将集合视图单元格的indexPath传递给另一个视图控制器

Question

I'm following a tutorial for making an Instagram-esque app, and the tutorial goes through how to display all data (image, author, likes, etc) all in one collection view. I'm trying to do it a little bit differently so only the images are displayed in the collection view, then if an image is tapped, the user is taken to a different view controller where the image plus all the other data is displayed.

So in my view controller with the collection view ( FeedViewController ), I have my array of posts declared outside the class ( Post is the object with all the aforementioned data):

var posts = [Post]()

Then inside the FeedViewController class, my cellForItemAt indexPath looks like this:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "postCell", for: indexPath) as! PostCell

    // creating the cell
    cell.postImage.downloadImage(from: posts[indexPath.row].pathToImage)

    photoDetailController.authorNameLabel.text = posts[indexPath.row].author
    photoDetailController.likeLabel.text = "\(posts[indexPath.row].likes!) Likes"
    photoDetailController.photoDetailImageView.downloadImage(from: posts[indexPath.row].pathToImage)

    return cell
}

And then I also obviously have a function to fetch the data which I can post if necessary, but I think the problem is because PhotoDetailController doesn't know the indexPath (although I may be wrong).

When I run the app and try to view the FeedViewController I get a crash fatal error: unexpectedly found nil while unwrapping an Optional value , highlighting photoDetailController.authorNameLabel line.

Am I correct in assuming the problem is because the indexPath is available only in the collection view data sources within FeedViewController ? If so, how can I pass that indexPath to PhotoDetailController so my code works correctly?

Thanks for any advice!

EDIT: Edited my didSelectItem method:

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    let photoDetailController = self.storyboard?.instantiateViewController(withIdentifier: "photoDetail") as! PhotoDetailController

    photoDetailController.selectedPost = posts[indexPath.row]

    self.navigationController?.pushViewController(photoDetailController, animated: true)
}

and cellForItemAt :

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "postCell", for: indexPath) as! PostCell


    cell.postImage.downloadImage(from: posts[indexPath.row].pathToImage)


    return cell
}

And in PhotoDetailController :

var selectedPost: Post! inside the class, then:

override func viewDidLoad() {
    super.viewDidLoad()

    self.authorNameLabel.text = selectedPost[indexPath.row].author
    self.likeLabel.text = "\(selectedPost[indexPath.row].likes!) Likes"
    self.photoDetailImageView.downloadImage(from: selectedPost[indexPath.row].pathToImage)
}

But still getting error use of unresolved identifier "indexPath

EDIT 2: Storyboard

Answer 1

You are getting this nil crash because this photoDetailController is not yet loaded so all its outlet are nil also the way currently you are doing is also wrong.

You need to add the controller code in didSelectItemAt method and perform the navigation.

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    let photoDetailController = self.storyboard?.instantiateViewController(withIdentifier: "YourIdentifier") as! PhotoDetailController  
    photoDetailController.selectedPost = posts[indexPath.row]
    self.navigationController?.pushViewController(photoDetailController, animated: true)
}

Now simply create one instance property of type Post with name selectedPost in PhotoDetailController and set all the detail from this selectedPost object in viewDidLoad of PhotoDetailController .

Edit: Set your viewDidLoad like this in PhotoDetailController

override func viewDidLoad() {
    super.viewDidLoad()

    self.authorNameLabel.text = selectedPost.author
    self.likeLabel.text = "\(selectedPost.likes!) Likes"
    self.photoDetailImageView.downloadImage(from: selectedPost.pathToImage)
}