can you spot the nil while unwrapping? - ios

Question

I'm trying to find where is the nil when unwrapping. Here is the piece of code I have. The lines where the fatal errors are found are at:
1st file:
date = dateFormatter().date(from: dictionary[kDATE] as! String)!
2nd file:
self.allLists.append(ShoppingList.init(dictionary: currentList))
This is from the shoppingList.swift file and the function is called in a controller
import Foundation
import Firebase
class ShoppingList{
let name: String
var totalPrice: Float
var totalItems: Int
var id: String
var date: Date
var ownerId: String
init(_name: String, _totalPrice: Float = 0, _id: String = "") {
name = _name
totalPrice = _totalPrice
totalItems = 0
id = _id
date = Date()
ownerId = "1234"
}
//creates shopping list item from this dictionary
init(dictionary: NSDictionary) {
name = dictionary[kNAME] as! String
totalPrice = dictionary[kTOTALPRICE] as! Float
totalItems = dictionary[kTOTALITEMS] as! Int
id = dictionary[kSHOPPINGLISTID] as! String
date = dateFormatter().date(from: dictionary[kDATE] as! String)!
ownerId = dictionary[kOWNERID] as! String
}
func dictionaryFromItem(item: ShoppingList) -> NSDictionary {
return NSDictionary(objects: [item.name, item.totalPrice, item.totalItems, item.id, dateFormatter().string(from: item.date), item.ownerId], forKeys: [kNAME as NSCopying, kTOTALPRICE as NSCopying, kTOTALITEMS as NSCopying, kSHOPPINGLISTID as NSCopying, kDATE as NSCopying, kOWNERID as NSCopying])
}
Here is the controller:
import UIKit
import KRProgressHUD
class AllListsViewController: UIViewController, UITableViewDataSource,UITableViewDelegate{
#IBOutlet weak var tableView: UITableView!
var allLists:[ShoppingList] = []
var nameTextField: UITextField!
override func viewDidLoad() {
super.viewDidLoad()
loadLists()
}
//MARK: TableView DataSource
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return allLists.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
let shoppingList = allLists[indexPath.row]
cell.textLabel?.text = shoppingList.name
return cell
}
//MARK: IBActions
#IBAction func addBarButonItemPressed(_ sender: Any) {
let alertController = UIAlertController(title: "Create Shopping List", message: "Enter the shopping list name", preferredStyle: .alert)
alertController.addTextField{ (nameTextField) in
nameTextField.placeholder = "Name"
self.nameTextField = nameTextField
}
let cancelAction = UIAlertAction(title: "Cancel", style: .cancel){ (action) in
}
let saveAction = UIAlertAction(title: "Save", style: .default){ (action) in
if self.nameTextField.text != ""{
self.createShoppingList()
}else{
KRProgressHUD.showWarning(message: "Name is empty!")
}
}
alertController.addAction(cancelAction)
alertController.addAction(saveAction)
self.present(alertController,animated: true, completion:nil)
}
//MARK: LoadList
func loadLists(){
//.values has all the info of the child
firebase.child(kSHOPPINGLIST).child("1234").observe(.value, with: {
snapshot in
self.allLists.removeAll()
//if we actually received smthing from firebase
if snapshot.exists(){
let sorted = ((snapshot.value as! NSDictionary).allValues as NSArray).sortedArray(using: [NSSortDescriptor(key: kDATE,ascending: false)])
for list in sorted {
let currentList = list as! NSDictionary
self.allLists.append(ShoppingList.init(dictionary: currentList))
}
} else {
print("no snapshot")
}
self.tableView.reloadData()
})
}
//MARK: Helper functions
func createShoppingList(){
let shoppingList = ShoppingList(_name: nameTextField.text!)
shoppingList.saveItemInBackground(shoppingList: shoppingList){ (error) in
if error != nil{
KRProgressHUD.showError(message: "Error creating shopping list")
return
}
}
}
}
Also the data formatter is a small function in another file.
import Foundation
import UIKit
private let dateFormat = "yyyyMMDDHHmmss"
func dateFormatter() -> DateFormatter {
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = dateFormat
return dateFormatter
}

Answer 1

So you have a forced downcast and a forced optional unwrap on this line:
date = dateFormatter().date(from: dictionary[kDATE] as! String)!
Either your dictionary isn't returning a string, or the string coming out of the dictionary isn't able to be processed as a date. My guess is it's the first problem as dates are often stored as epoch.
Try this instead of the line above. Add a breakpoint at the top and step through:
print(dictionary[kDATE])
if let dictValue = dictionary[kDATE] as? String {
print(dictValue)
if let unwrappedDate = dateFormatter().date(from: dictValue) {
date = unwrappedDate
}
}
If it fails on the first if-let then the return value is not a string. If it fails on the second the problem lies with the date formatter being unable to read the format.
The first print might give you a clue as to what type to cast to, the second could help you fix the format.
Try to be careful when force unwrapping,
optionalVar!
or for downcasting.
unknownType as! Type
You should really only "use the force" when you're absolutely sure there's no way the value will be nil.