String not being passed to next view controller from prepareForSegue - ios

Question

I have a push segue on my StoryBoard which is named toGuestVC.
I use that to segue to the next ViewController in my didSelectRowAtIndexPath method like so:
override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
let username = followUsernameArray[indexPath.row]
performSegue(withIdentifier: SG_TO_GUEST_VIEW_CONTROLLER, sender: username)
}
Then in my prepareForSegue:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == SG_TO_GUEST_VIEW_CONTROLLER {
if let nextVC = segue.destination as? GuestCollectionVC, let sender = sender as? String {
print("PRINTING NEXT VC: \(nextVC)") //This prints out the memory address. Not sure if this is what you meant by print nextVC.
nextVC.guestUser = sender
}
}
}
For some reason this line in my prepareForSegue is not running:
nextVC.guestUser = sender.username
When I try to print out the value guestUser in my nextViewController the value of guestUser is nil. But when I print out the value of sender in my prepareForSegue method it is not nil.
So is my sender value not being passed to the next ViewController? I can't find a solution to this problem any ideas?
GuestCollectionVC Implementation:
import UIKit
import Parse
private let reuseIdentifier = "Cell"
class GuestCollectionVC: UICollectionViewController {
var guestUser: String!
override func viewDidLoad() {
super.viewDidLoad()
print("PRINTING SELF IN GuestCollectionVC: \(self)")
loadPosts()
}
func loadPosts() {
//Load posts query
let query = PFQuery(className: PF_POSTS_CLASS)
query.limit = postCount
//Getting error here below this comment when I use guestUser since it is nil
query.whereKey(PF_POSTS_USERNAME_COLUMN, equalTo: guestUser)
query.findObjectsInBackground { (result: [PFObject]?, error: Error?) -> Void in
if error == nil {
if let result = result {
self.uuidOfPosts.removeAll(keepingCapacity: false)
self.imageArrayOfPFFIle.removeAll(keepingCapacity: false)
for postObject in result {
if let uuid = postObject[PF_POSTS_UUID_COLUMN] as? String, let pic = postObject[PF_POSTS_PIC_COLUMN] as? PFFile {
self.uuidOfPosts.append(uuid)
self.imageArrayOfPFFIle.append(pic)
}
}
self.collectionView?.reloadData()
}
}else if error != nil {
print("ERROR FROM GUEST COLLECTION VC FROM loadPosts FUNCTION: \(error?.localizedDescription)")
}
}
}
}
So this is my implementation in the GuestViewController. In my loadPosts method where I used the variable guestUser I am getting the error:
fatal error: unexpectedly found nil while unwrapping an Optional value

Answer 1

From console printing
PRINTING NEXT VC: "InstagramClone.GuestCollectionVC: 0x7a6c5cc0"
PRINTING SELF IN GuestCollectionVC: "InstagramClone.GuestCollectionVC: 0x7a6c5100"
it's now obvious that hidden unexpected instance of GuestCollectionVC was created. So, there are different errors occurs depending on order of this two objects invoke their viewDidLoad method (can be any order). Also there are can be other errors in nextVC viewDidLoad method, but this is other story for other question.
You got this problems because you created action segue, that works automatically on cell click (hidden view controller created), and at the same time you are perform this segue in code, creating second controller nextVC.
To solve issue, you should find and remove that segue and add new one, not action segue from some element of your view controller, but "empty" segue between view controllers. To create segue of this type you should select first view controller, hold "control" key and start dragging to next view controller from yellow square on top of first view controller (that symbol controller itself), choose "show", and set identifier.

Answer 2

Since I don't have the full context of the values within your tableView method I can only speculate. That said, the sender you're passing in should be the view controller:
performSegue(withIdentifier: "toGuestVC", sender: username)
You're passing in a value called username which looks to be a string value? It should be something like:
performSegue(withIdentifier: "toGuestVC", sender: self)
where self is your view controller. If you're passing in a string value to sender then in your prepareForSegue method then sender does not have a property called username sender actually is username. Therefore you should pass the value elsewhere:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let indexPath = self.tableView.indexPathForSelectedRow
if let nextVC = segue.destination as? GuestCollectionVC {
nextVC.guestUser = followUsernameArray[indexPath.row]
}
}