how to retrive data from firebase realtime database as a list

Question

I am working on an Android project and have a button that inserts data into the Realtime Database child and it's working fine. but now i need to get that data as a list and append it to listof to be able then to display it in a lazyColumn. here are images from Firebase and Kotlin files

have seen many ways to add data but couldn't find any solution about how to get data as a list. here is my last code update : when i click display, my app get crush. could you please check what's missing here

fun Greeting() {
val mydb = Firebase.database.reference
var authorText by remember { mutableStateOf("") }
var contentText by remember { mutableStateOf("") }
var myList = mutableListOf<Message>()

Column(modifier = Modifier.fillMaxSize()) {
    TextField(value = authorText, onValueChange = {authorText=it})
    TextField(value = contentText, onValueChange = {contentText=it})
    
    Button(onClick = {
        val message = Message(authorText,contentText)
        mydb.child("messages").push().setValue(message) }) {
        Text(text = "insert")
    }
    Button(onClick = {
        val rf = mydb.child("messages")
        rf.get().addOnCompleteListener {
            if (it.isSuccessful) {
                val snapshot = it.result
                val messages = mutableListOf<Message>()
                for (messageSnapshot in snapshot.children) {
                    val message = messageSnapshot.getValue(Message::class.java)
                    messages.add(message!!)
                }
                myList=messages

            } else {
                Log.d(TAG, "${it.exception?.message}") //Never ignore potential errors!
            }
        }
        
        }) { Text(text = "display")
    }
    LazyColumn {
        items(myList){
            Row {
                Text(text = it.author)
                Spacer(modifier = Modifier.width(2.dp))
                Text(text = it.content)
            }
        }
    }
}

} data class Message(var author:String,var content:String)

Answer 1

Because you said in the last comment that you're looking for a solution to read the data under the messages node on Android, then please check the below solution using Kotlin:

val db = Firebase.database.reference
val messagesRef = db.child("messages")
messagesRef.get().addOnCompleteListener {
    if (it.isSuccessful) {
        val snapshot = it.result
        for (messageSnapshot in snapshot.children) {
            val author = messageSnapshot.getValue(String::class.java)
            val content = messageSnapshot.getValue(String::class.java)
            Log.d(TAG, "$author/$content")
        }
    } else {
        Log.d(TAG, "${it.exception?.message}") //Never ignore potential errors!
    }
}

So as you can see, you have to create a reference that points to the messages node, call get(), and then iterate through all children to get the data. However, this solution will work only if the messages node is a direct child of your root reference.

Or if you already have a clas called Message and you want to create a list of messages, then you can use:

val db = Firebase.database.reference
val messagesRef = db.child("messages")
messagesRef.get().addOnCompleteListener {
    if (it.isSuccessful) {
        val snapshot = it.result
        val messages = mutableListOf<Message>()
        for (messageSnapshot in snapshot.children) {
            val message = messageSnapshot.getValue(Message::class.java)
            messages.add(message!!) //
        }
        Log.d(TAG, "${messages.size}") //
    } else {
        Log.d(TAG, "${it.exception?.message}") //Never ignore potential errors!
    }
}

The result in your logcat will be:

2