Update Array [[String: [Dictionary]]] when valueChanged in Firebase - ios

Question

var chatMessages = [[String: ChatMessage]]()
Firebase Chat Messages structure is like this.
-Kjws99ol6qjFt7ET9C
content: "Hehd"
displayName: "John Doe"
fileLength: 0
fileUrl: ""
fromID: "5904ee8cfa"
isRead: false
messageStatus: 2
messageType: "normal"
timestamp: 1494596232
Now on childAdded I'm appending the new message like this
weakSelf.chatMessages.append(newMessage)
//Kjws99ol6qjFt7ET9C - This is the threadID which is stored in String and below value is stored in ChatMessage
But after message isRead by user it value changes and that is identified by childChanged so in childChanged change how to update my Array correctly?

Answer 1

On the childChanged event, the app is passed a snapshot of the updated child, with the (in this case) key being Kjws99ol6qjFt7ET9C and the value being the child node data.
To update the array, find which index in the chatMessages array corresponds to that key and update the value accordingly.
To find it in the array you've set up, which is an array of [String: ChatMessage] dictionaries do the following
let searchKey = "Kjws99ol6qjFt7ET9C"
let index = chatMessages.map( {$0.keys.first!} ).index(of: searchKey)
Once you have the index, you can then update the element in the array with the new data.
{$0.keys.first!} - compiles all of the keys in the chatMessage array into an array
index(of: searchKey) - finds the index of the searchKey we are looking for
Then you can
chatMessage[index] = updated data
If you need any additional code, let me know.
However, I would strongly encourage changing the model to store a ChatMessage class (or struct) in the array
class ChatMessage {
var fbKey = "" // the key like Kjws99ol6qjFt7ET9C
var content = "" // like "Hehd"
var displayName "" // "John Doe"
}
var chatMessages = [ChatMessage]()
it will be easier to maintain and the array search is simplified and faster.
With this use case, to find a specific index do this
let searchKey = "Kjws99ol6qjFt7ET9C"
let index = chatMessages.index(where: { $0.fbKey == searchKey} )

Answer 2

I'm confused as to why you are storing the dictionary inside an array. It looks to me like
var chatMessages = [String: ChatMessage]()
would satisfy your model as each message push id (e.g. -Kjws99ol6qjFt7ET9C) would be unique from the database, so you could have a valid Dictionary by storing this push id as the key.
When you receive a childChanged event, you can then quickly locate the message that has changed by looking up the snapshot.key in the dictionary and updating it.