issues loading items from firebase to a pickerview - swift

Question

I have successfully created a QuestionModel class which retrieves items from firebase such, as a Question, string of answers and a correct question. I am however now having difficulty in terms of getting these items to go into a picker view from another class. The class called QuestionsViewController is where I am having an issue in terms of using the questions class to retrieve data from. The QuestionModel class contains retrieving data from firebase. I am having bad execution errors throughout the code in the QuestionsViewController class. This mainly occurs when trying to set the itemlabel text before the pickverview and code for the pickerview functions.
import Foundation
import Firebase
import FirebaseDatabase
import FirebaseAuth
import CoreData
class QuestionList
{
//properties
public static var Username: String = ""
private static var quiz = [Question]()
static func getDummyQuestions()->[Question]
{
//create some dummy data for the model
var ref: FIRDatabaseReference!
var refHandle: UInt!
ref = FIRDatabase.database().reference() //reference
refHandle = ref.child("Questions").child("Q1").observe(.value, with: { (snapshot)in
if let dataDict = snapshot.value as? [String: Any] {
if let quest = dataDict["Question"] as? String,
let Answers = dataDict["Answers"] as? [String],
let Correct = dataDict["Correct"] as? Int {
quiz.append(Question(q: quest, a: Answers, c: Correct))
}
print (dataDict)
}
})
return quiz
}
}
class Question {
var quest:String
var answers:[String]
var correct:Int
init(q: String, a:[String], c:Int)
{
quest = q
answers = a
correct = c
}
func isCorrectQuestion(itemSelected: String)->Bool {
if (itemSelected == answers[correct]) {
return true
} else {
return false
}
}
}
import UIKit
import Firebase
import FirebaseAuth
class QuestionsViewController: UIViewController, UIPickerViewDelegate {
#IBOutlet weak var usernamelabel: UILabel! //sets username label
#IBOutlet weak var Next: UIButton! //next button
#IBOutlet weak var itemLabel: UILabel! //item user has selected
#IBOutlet weak var Question: UILabel! //sets question label
#IBOutlet weak var pickerview: UIPickerView! //sets picker view
public var totalQuestions: Int = 0 //sets total question to 0
public var currentQuestion = 0 //sets current question to 0
public var totalCorrect: Int = 0 //sets totalcorrect to 0
var itemSelected: String = "" //item selected
var LabelText = String()
let Exam = QuestionList() //uses the questions class for instances
var Questions = QuestionList.getDummyQuestions()
var ref: FIRDatabaseReference!
var refHandle: UInt!
override func viewDidLoad() {
super.viewDidLoad() //when the app is loaded
ref = FIRDatabase.database().reference() //reference
refHandle = ref.child("Questions").observe(.value, with: { (snapshot)in
let dataDict = snapshot.value as! [String: AnyObject]
print (dataDict)
})
usernamelabel.text = LabelText //username
pickerview.delegate = self
itemLabel.text = "" //loads the item label of whats selected
itemSelected = QuestionList.getDummyQuestions()[currentQuestion].answers[0] //initially when loaded first item is selected
Question.text = QuestionList.getDummyQuestions()[currentQuestion].quest
}
func numberOfComponents(in pickerView: UIPickerView) -> Int {
return 1 //return one component from the picker
}
func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int{
return QuestionList.getDummyQuestions()[currentQuestion].answers.count
}
func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String?{
return QuestionList.getDummyQuestions(). [currentQuestion].answers[row]
}
func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int){
itemSelected = QuestionList.getDummyQuestions(). [currentQuestion].answers[row]
}
#IBAction func NextAction(_ sender: Any){
currentQuestion = currentQuestion + 1 //moves onto next question and increments
if (QuestionList.getDummyQuestions()[currentQuestion].isCorrectQuestion(itemSelected: itemSelected)) {
totalCorrect += 1
itemLabel.text = String(totalCorrect) + "/" + String(totalQuestions)
}
if(currentQuestion < QuestionList.getDummyQuestions().count) {
pickerview.reloadAllComponents()
itemSelected = QuestionList.getDummyQuestions()[currentQuestion].answers[1]
Question.text = QuestionList.getDummyQuestions() [currentQuestion].quest
} else {
pickerview.isHidden = true
Question.text = "You have finished"
Next.isHidden = true
}
}
}

Answer 1

Firebase functions do not (and should not) return values as they are asynchronous.
So the return quiz line will fail most of the time as it will try to return data before Firebase has had time to retrieve it from the server.
When coding with Firebase, data is only valid inside the closure following the function. So for example, this what NOT to do:
func someFunc() {
ref.child("Questions").child("Q1").observe(.value, with: { snapshot in
print(snap)
})
print(snap) //this will not print the snap as this line executes *before* the closure
}
So doing it the right way; retrieve the data from Firebase, populate the array and refresh the tableview all within the closure.
static func populateArrayAndRefreshTableView()
{
var ref: FIRDatabaseReference!= FIRDatabase.database().reference()
let questionsRef = ref.child("Questions")
questionsRef.child("Q1").observeSingleEvent(of: .value, with: { snapshot in
if let dataDict = snapshot.value as? [String: Any] {
let quest = dataDict["Question"] as? String,
let Answers = dataDict["Answers"] as? [String],
let Correct = dataDict["Correct"] as? Int {
self.quizArray.append(Question(q: quest, a: Answers, c: Correct))
self.tableView.reloadData()
}
})
}
}
Also note that the original code was using observe(.value). That will leave an observer attached to the ref and if the question changes, the code will be called. It doesn't look like that should be the behavior so using observeSingleEvent will call it once without adding an observer.
Finally - you may want to re-consider how the nodes are named in your structure. It's often best practice to disassociate node name keys from the data they contain.
questions
-UYiuokoksokda
question: "What significant contribution to bioengineering was made on the Loonkerian outpost on Klendth?"
correct_answer: answer_1
answers:
answer_0: "Left handed smoke shifter"
answer_1: "The universal atmospheric element compensator"
answer_2: "Warp coil nullification amplifier"
answer_3: "H.A.L. 9000"
-YY8jioijasdjd
question: "What is Kiri-kin-tha's first law of metaphysics?"
correct_answer: answer_2
answers:
answer_0: "No matter where you go, there you are"
answer_1: "Only people with sunroofs use them"
answer_2: "Nothing unreal exists"
answer_3: "Gravity is heavy"
The keys, UYiuokoksokda, are created with childByAutoId().
If you need to query answers you may want to even denormalize them into their own node and use the question key as the node key for the answers or keep a child node with the question key.