我已经成功创建了一个QuestionModel类，它从firebase中检索项目，如问题，答案字符串和正确的问题。然而，我现在在让这些项目从另一个班级进入选择器视图方面遇到困难。名为QuestionsViewController的类是我在使用问题类从中检索数据方面遇到问题的地方。 QuestionModel类包含从firebase检索数据。我在QuestionsViewController类的代码中遇到了错误的执行错误。这主要发生在尝试在pickverview之前设置itemlabel文本和pickerview函数的代码时。
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
}
}
}
答案 0 :(得分：1)
Firebase函数不会（也不应该）返回值，因为它们是异步的。
因此，返回测验行大多数时间都会失败，因为它会在Firebase有时间从服务器检索数据之前尝试返回数据。
使用Firebase进行编码时，数据仅在函数后面的闭包内有效。所以，例如，这不做什么：
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
}
这样做是正确的;从Firebase检索数据，填充数组并在闭包内刷新tableview。
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()
}
})
}
}
另请注意，原始代码使用了observe（.value）。这将使观察者附加到ref，如果问题发生变化，将调用代码。它看起来不应该是行为，因此使用observeSingleEvent将调用它一次而不添加观察者。
最后 - 您可能需要重新考虑如何在结构中命名节点。通常最佳做法是将节点名称密钥与它们包含的数据解除关联。
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"
密钥UYiuokoksokda是使用childByAutoId（）创建的。
如果您需要查询答案，您可能希望将它们归一化到自己的节点中，并使用问题密钥作为答案的节点键，或者使用问题密钥保留子节点。