Xcode: Why is my optional value nill while unwrapping?

Question

Can someone please look trough my code and tell me why my value is nil. If you need me to post other files I will. The project is mostly firebase and the app crashes whenever you try to post within the application. I believe it is crashing when the screen has to be updated because the data is hitting the database.

import UIKit
import FirebaseFirestore

class FeedVC: UITableViewController {



    var db = Firestore.firestore()
    var postArray = [Posts]()

    override func viewDidLoad() {
        super.viewDidLoad()

        //db = Firestore.firestore()
//loadData()
      // checkForUpdates()


    }
       override func viewDidAppear(_ animated: Bool){
        loadData()
        checkForUpdates()


    }

    func loadData() {
        db.collection("posts").getDocuments() {
            querySnapshot, error in
            if let error = error {
                print("\(error.localizedDescription)")
            }else{
                self.postArray = querySnapshot!.documents.flatMap({Posts(dictionary: $0.data())})
                DispatchQueue.main.async {
                    self.tableView.reloadData()
                }
            }
        }


    }

    func checkForUpdates() {
        db.collection("posts").whereField("timeStamp", isGreaterThan: Date())
            .addSnapshotListener {
                querySnapshot, error in

                guard let snapshot = querySnapshot else {return}

                snapshot.documentChanges.forEach {
                    diff in

                    if diff.type == .added {
                        self.postArray.append(Posts(dictionary: diff.document.data())!)
                        DispatchQueue.main.async {
                            self.tableView.reloadData()
                        }
                    }
                }

        }
    }

    @IBAction func composePost(_ sender: Any) {






        let composeAlert = UIAlertController(title: "New Post", message: "Enter your name and message", preferredStyle: .alert)

        composeAlert.addTextField { (textField:UITextField) in
            textField.placeholder = "Your name"
        }

        composeAlert.addTextField { (textField:UITextField) in
            textField.placeholder = "Your message"
        }

        composeAlert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))

        composeAlert.addAction(UIAlertAction(title: "Send", style: .default, handler: { (action:UIAlertAction) in

            if let name = composeAlert.textFields?.first?.text, let content = composeAlert.textFields?.last?.text {

                let newSweet = Posts(name: name, content: content, timeStamp: Date())

                var ref:DocumentReference? = nil
                ref = self.db.collection("posts").addDocument(data: newSweet.dictionary) {
                    error in

                    if let error = error {
                        print("Error adding document: \(error.localizedDescription)")
                    }else{
                        print("Document added with ID: \(ref!.documentID)")
                    }

                }

            }

        }))

        self.present(composeAlert, animated: true, completion: nil)


    }



    // MARK: - Table view data source
    override func numberOfSections(in tableView: UITableView) -> Int {

        return 0
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

        return postArray.count
    }


    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)

        let sweet = postArray[indexPath.row]

        cell.textLabel?.text = "\(sweet.name): \(sweet.content)"
        cell.detailTextLabel?.text = "\(sweet.timeStamp)"

        return cell
    }
  }

import Foundation
import FirebaseFirestore

protocol DocumentSerializable  {
    init?(dictionary:[String:Any])
}


struct Posts {
    var name:String
    var content:String
    var timeStamp:Date

    var dictionary:[String:Any] {
        return [
            "name":name,
            "content" : content,
            "timeStamp" : timeStamp
        ]
    }

}

extension Posts : DocumentSerializable {
    init?(dictionary: [String : Any]) {
        guard let name = dictionary["name"] as? String,
            let content = dictionary["content"] as? String,
            let timeStamp = dictionary ["timeStamp"] as? Date else {return nil}

        self.init(name: name, content: content, timeStamp: timeStamp)
    }
}

Answer 1

use TimeStamp instead of Date

 import FirebaseFirestore 
    guard let stamp = data["timeStamp"] as? Timestamp else { return nil }

---

Answer 2

This is the line that's crashing according to the comments...

self.postArray.append(Posts(dictionary: diff.document.data())!)

and it's crashing because you are force-unwrapping a variable that's nil

Posts(dictionary: diff.document.data())! <- ! means 'I guarantee you will never be nil'

And it's nil because of this Posts extension...

extension Posts : DocumentSerializable {
    init?(dictionary: [String : Any]) {
        guard let name = dictionary["name"] as? String,
            let content = dictionary["content"] as? String,
            let timeStamp = dictionary ["timeStamp"] as? Date else {return nil}

and the offending code is here

guard 
   let name = dictionary["name"] as? String,
   let content = dictionary["content"] as? String,
   let timeStamp = dictionary ["timeStamp"] as? Date 

else {return nil} //OFFENDING CODE!

If any one of those vars is not present in the dictionary, it fails, and returns nil.

So... one of your documents does not contain one of those fields.

You may also want to refer to the Firestore Guide on how to write dates. Check out the example code in Add Data

Also, Firestore doesn't have an internal Date type so use Timestamp.dateValue instead. See it here Timestamp