How to execute two completion blocks in a single function and pass the data of the completion block to next view controller? - swift

Question

This is my database structure:
I'm using a function with closure, performing two completion blocks and store the data in two separate arrays. Once I get the data I want to pass the data to next view controller into different variables, but instead I'm getting same value for both arrays.
#IBAction func GoToAnswerPage(_ sender: Any) {
self.getData(refe:JoinCodeTextField.text!) { (array) in
self.performSegue(withIdentifier:"JoinToAnswerPage",sender:array)
}
}
func getData(refe: String, completion: #escaping (([Any]) -> ())) {
var questionArray = [Any]()
var answerArray = [Any]()
let ref = Database.database().reference(fromURL: "https://pollapp-30419.firebaseio.com/").child("Questions/\(refe)/")
ref.child("Question_And_Options").observeSingleEvent(of: .value,with: { snapshot in
let enumerator = snapshot.children
while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{
questionArray.append(value)
}
completion(questionArray)
})
ref.child("Answer_Key").observeSingleEvent(of: .value,with: { snapshot in
let enumerator = snapshot.children
while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{
answerArray.append(value)
}
completion(answerArray)
})
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
guard let joinViewController = segue.destination as? JoinAnswerViewController
else {
return
}
joinViewController.answers = sender as! [String]
joinViewController.options = sender as! [String]
}
On the next view controller.
var options = [Any]()
var answers = [Any]()
This is the output I'm getting:
answers-["Test Q-1", "Test A-1", "Test A-2"]
questions-["Test Q-1", "Test A-1", "Test A-2"]
answers-["Test A-1"]
questions-["Test A-1"]
Instead I should get:
questions-["Test Q-1", "Test A-1", "Test A-2"]
answers-["Test A-1"]

Answer 1

Your completion handler will be called twice, once for "answers" and once for "questions". They could come in either order, so you should pass an additional type in the completion to know which you have received. Use a [String : [Any]] dictionary to collect the two arrays, and call self.performSegue(withIdentifier:sender:) when you've received both arrays and stored them in the dictionary arrays.
In prepare(for:sender:) unpack the sender dictionary and assign the values:
#IBAction func GoToAnswerPage(_ sender: Any) {
var arrays = [String : [Any]]()
self.getData(refe: JoinCodeTextField.text!) { (array, type) in
arrays[type] = array
if arrays.count == 2 {
self.performSegue(withIdentifier:"JoinToAnswerPage",sender: arrays)
}
}
}
func getData(refe: String, completion: #escaping (([Any], String) -> ())) {
var questionArray = [Any]()
var answerArray = [Any]()
let ref = Database.database().reference(fromURL: "https://pollapp-30419.firebaseio.com/").child("Questions/\(refe)/")
ref.child("Question_And_Options").observeSingleEvent(of: .value,with: { snapshot in
let enumerator = snapshot.children
while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{
questionArray.append(value)
}
completion(questionArray, "question")
})
ref.child("Answer_Key").observeSingleEvent(of: .value,with: { snapshot in
let enumerator = snapshot.children
while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{
answerArray.append(value)
}
completion(answerArray, "answer")
})
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
guard let joinViewController = segue.destination as? JoinAnswerViewController
else {
return
}
guard let arrays = sender as? [String : [Any]],
let answers = arrays["answer"] as? [String],
let questions = arrays["question"] as? [String]
else { return }
joinViewController.answers = answers
joinViewController.options = questions
}
Note: When the user presses a button, they should get an immediate response. Since you are loading the data from the network, there may be a delay making the user wonder if anything is happening. It would be better to pass JoinCodeTextField.text! to JoinAnswerViewController and let it load the question/answer data. JoinAnswerViewController could display a UIActivityIndicatorView (spinner) while the data is loading to let the user know the data is coming. Once you have both arrays, you can set up the JoinAnswerViewController.