Can't access Firebase child - ios

Question

I have a firebase database reference
FIRDatabase.database().reference().child("messages").child("\(self.convoId!)").childByAutoId()
I want to access the ReceiverName from my firebase database in DisplayViewController, but when I call the database reference, I get an error because of convoId. This is how convoId was declared (in MessagesViewController).
override func viewDidLoad() {
super.viewDidLoad()
let receiverId = receiverData as! String
let receiverIdFive = String(receiverId.characters.prefix(5))
let senderIdFive = String(senderId.characters.prefix(5))
if (senderIdFive > receiverIdFive)
{
self.convoId = senderIdFive + receiverIdFive
}
else
{
self.convoId = receiverIdFive + senderIdFive
}
}
receiverData was passed from UserviewController to MessagesViewController and "senderId" is the string identifier that uniquely identifies the current user sending messages and is automatically declared in JSQMessagesViewController.h. so essentially, I can't redeclare convoId in my DisplayViewController. However, in DisplayViewController, I need to access ReceiverName.
This is how I attempted to retrieve ReceiverName:
let rootRef = FIRDatabase.database().reference()
rootRef.child("messages").observeSingleEvent(of: .value) {
(snapshot: FIRDataSnapshot) in
let loggedInUserData = snapshot
if let postsDictionary = snapshot .value as? [String: AnyObject] {
for post in postsDictionary {
self.messages.add(post.value)
}
self.MessageTableView.reloadData()
}
}
Then I populate the derived data in a tableviewcell:
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "MessageCell", for: indexPath) as! MessageTableViewCell
//Configure the cell
print(messages[indexPath.row])
let message = self.messages[indexPath.row] as! [String: AnyObject]
cell.SellerName.text = message["ReceiverName"] as? String
return cell
}

Answer 1

Try this inside your observeSingleEvent function:
...
for post in postsDictionary {
let messages = post.value as! [String: AnyObject]
for (id, value) in messages {
let info = value as! [String: AnyObject]
let receiver = info["ReceiverName"]!
print("\(id): \(receiver)")
self.messages.add(value)
}
}
...