Firebase / Firestore not getting document and running code - ios

Question

I am getting a document from firebase in swift. However the line isn't being run and is not getting the data.
This is my code:
let db = Firestore.firestore()
db.collection("chats").document(userDefaults.string(forKey: "currentGroup")!).collection("messages").document("variable").getDocument { (document, error) in
if error != nil{
print("error getting document")
}
else{
let documentData = document!.data()
let startNumOfMessages = documentData!["numOfMessages"] as! Int
var messageArray: Array<String> = []
if startNumOfMessages > 0 {
for message in 1...startNumOfMessages{
print(message)
//THIS LINE ISNT RUNNING
db.collection("chats").document(self.userDefaults.string(forKey: "currentGroup")!).collection("messages").document("\(message)").getDocument { (messageDoc, err) in
if err != nil{
print("Error getting message \(message)")
}
else{
if messageDoc!.exists && messageDoc != nil{
let messData = messageDoc!.data()
print(messData!["message"]!)
messageArray.append(messData!["message"] as! String)
}
else{
print("error in document")
}
}
}
}
//Display them
for num in 0...messageArray.count{
let label = UILabel()
label.text = messageArray[num]
self.stackView.addArrangedSubview(label)
}
}
}
}
The line below the comment is the line that isn't running. And the line that says label.text = messageArray[num] displays an error
Fatal error: Index out of range
Showing it doesn't get the data.

Answer 1

You miss the asynchronous way use DispatchGroup ( numbered from 1 to 4 )
let db = Firestore.firestore()
db.collection("chats").document(userDefaults.string(forKey: "currentGroup")!).collection("messages").document("variable").getDocument { (document, error) in
if error != nil{
print("error getting document")
}
else{
let documentData = document!.data()
let startNumOfMessages = documentData!["numOfMessages"] as! Int
var messageArray: Array<String> = []
if startNumOfMessages > 0 {
let g = DispatchGroup() /// 1
for message in 1...startNumOfMessages{
print(message)
//THIS LINE ISNT RUNNING
g.enter() /// 2
db.collection("chats").document(self.userDefaults.string(forKey: "currentGroup")!).collection("messages").document("\(message)").getDocument { (messageDoc, err) in
if err != nil{
print("Error getting message \(message)")
}
else{
if messageDoc!.exists && messageDoc != nil{
let messData = messageDoc!.data()
print(messData!["message"]!)
messageArray.append(messData!["message"] as! String)
}
else{
print("error in document")
}
}
g.leave() /// 3
}
}
g.notify(queue: .main) { /// 4
//Display them
for num in 0...messageArray.count{
let label = UILabel()
label.text = messageArray[num]
self.stackView.addArrangedSubview(label)
}
}
}
}
}