Chat messages does not load properly - ios

Question

i have tried to create a chat message system but the old messages seems to still remain when the new messages are called.
Anyone can help? Furthermore, sometimes when a new user is created and he chat with another user.The messages from the other user is not reflected in the new user chat.
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
navigationItem.title = "Chat"
DispatchQueue.global(qos:.userInteractive).async {
DispatchQueue.main.async {
self.loadPosts()
self.loadPostsReceivedMessage()
}
}
}
//Get Message sent
func loadPosts() {
let senderIDNumber = Auth.auth().currentUser?.uid
let chatsRef = db.collection("chats").order(by: "timestamp", descending: false)
chatsRef.whereField("senderID", isEqualTo: senderIDNumber!).whereField("receiverID", isEqualTo: receiverIDNumber)
.addSnapshotListener { querySnapshot, error in
guard let documents = querySnapshot?.documents else {
print("Error fetching documents: \(error!)")
return
}
for document in documents {
let messageText = document.data()["message"] as? String
let senderIDNumber = document.data()["senderID"] as? String
let receiverIDNumber = document.data()["receiverID"] as? String
let timestamp = document.data()["timestamp"] as? String
guard let sender = document.data()["sender"] as? String else {return}
// let conversationsCounter = document.data()["conversationsCounter"] as? Int
guard let profileUrl = document.data()["profileUrl"] as? String else { return}
let chat = Chat(messageTextString: messageText!, senderIDNumber: senderIDNumber!, receiverIDNumber: receiverIDNumber!, timeStampString: timestamp!, profileImageUrl: profileUrl, senderString: sender)
self.chats.append(chat)
print(self.chats)
self.collectionView.reloadData()
}
}
}
//Get message received
func loadPostsReceivedMessage() {
/* let uid = Auth.auth().currentUser?.uid
let ref = Database.database().reference()
ref.child("users").child(uid!).observeSingleEvent(of: .value, with: { (snapshot) in
if let dic = snapshot.value as? [String: AnyObject]{
let currentUser = dic["username"] as? String
let senderIDNumber = Auth.auth().currentUser?.uid
} */
let chatsRef = db.collection("chats").order(by: "timestamp", descending: false)
print("thecurrentreceiver"+senderString)
print("thecurrentsender"+receiverIDNumber)
chatsRef.whereField("receiverID", isEqualTo: senderString).whereField("sender", isEqualTo: receiverIDNumber)
.addSnapshotListener { querySnapshot, error in
guard let documents = querySnapshot?.documents else {
print("Error fetching documents: \(error!)")
return
}
for document in documents {
let messageText = document.data()["message"] as? String
let senderIDNumber = document.data()["senderID"] as? String
let receiverIDNumber = document.data()["receiverID"] as? String
let timestamp = document.data()["timestamp"] as? String
// let conversationsCounter = document.data()["conversationsCounter"] as? Int
guard let profileUrl = document.data()["profileUrl"] as? String else { return}
guard let sender = document.data()["sender"] as? String else {return}
let chat = Chat(messageTextString: messageText!, senderIDNumber: senderIDNumber!, receiverIDNumber: receiverIDNumber!, timeStampString: timestamp!,profileImageUrl: profileUrl, senderString: sender)
print("whatisthemessage"+messageText!)
self.chats.append(chat)
print(self.chats)
self.chats.sort{$0.timestamp < $1.timestamp}
self.collectionView.reloadData()
}
}
}

Answer 1

You're using addSnapshotListener, which means that your callback gets called every time something relevant in the database changes. And when that happens, you loop over all the documents that match your query and add them to your view. This means that if there are multiple changes, you're adding most messages multiple times.
There are two common solutions:
Clear the view every time your callback gets called.
Only modify the view for the changes each time your callback gets called.
We'll use #2 below, since it is more efficient. Note that I'm only handling new messages to keep things simple. As you make your app more complete, you will also need to handle other types of changes, e.g. when a user deletes or updates a chat message.
let chatsRef = db.collection ("chats").order (by: "timestamp", descending: false)
chatsRef.whereField ("senderID", isEqualTo: senderIDNumber!)
.whereField ("receiverID", isEqualTo: receiverIDNumber)
.addSnapshotListener {
querySnapshot,
error in guard let documentChanges = querySnapshot?.documentChanges else {
print ("Error fetching documents: \(error!)")
return
}
for documentChange in documentChanges {
if (documentChange.type == .added) {
let data = documentChange.document.data ()
let messageText = data["message"] as? String
let senderIDNumber = data["senderID"] as? String
let receiverIDNumber = data["receiverID"] as? String
let timestamp = data["timestamp"] as? String
...
let chat = Chat (
messageTextString : messageText!,
senderIDNumber : senderIDNumber!,
receiverIDNumber : receiverIDNumber!,
timeStampString : timestamp!,
profileImageUrl : profileUrl,
senderString : sender
)
self.chats.append (chat)
print (self.chats)
self.collectionView.reloadData ()
}
}
}
For some more on this, have a look at responding to changes in the Firebase documentation.