how to retrive data from firebase realtime database as a list

alihamad
April 1, 2024
246 views
0 votes
2 Answers

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)

Answers

Chosen as BEST ANSWER

I did a little one change on Alex Mamo code .I don't know if its correct way, but it works for me.

fun Greeting() {
val cntx = LocalContext.current
val mydb = Firebase.database
val messages = remember { mutableStateListOf<Message>() } // 👈
var authorText  by remember { mutableStateOf("") }
var contentText  by remember { mutableStateOf("") }

Column {
    Spacer(modifier = Modifier.height(5.dp))
    TextField(value = authorText, onValueChange = {authorText=it})
    TextField(value = contentText, onValueChange = {contentText=it})
    // ------------------------------------------------------------- Adding to List
    Button(onClick = {
        val myref = mydb.getReference("messages")
        var newRecord = Message(authorText,contentText)
        myref.push().setValue(newRecord)
            .addOnSuccessListener {
                authorText=""
                contentText=""
                Toast.makeText(cntx,"successful", Toast.LENGTH_LONG).show() }
            .addOnFailureListener { Toast.makeText(cntx,"Error", Toast.LENGTH_LONG).show() }
    }) { Text(text = "Add") }
    // ------------------------------------------------ Click to show List
    Button(onClick = {
        val ref = mydb.getReference("messages")
        ref.get().addOnCompleteListener {
            if (it.isSuccessful) {
                val snapshot = it.result
                //  val messages = mutableListOf<CarClass>() 👈
                for (messageSnapshot in snapshot.children) {
                    val message = messageSnapshot.getValue(Message::class.java)
                    messages.add(message!!)
                }


            } else {
                Toast.makeText(cntx,"Error", Toast.LENGTH_LONG).show()

            }

        }

    }) { Text(text = "Show List") }
    Spacer(modifier = Modifier.height(10.dp))
    // ------------------------------------------------- Showing List Here 
    LazyColumn {
        items(messages.reversed()){
            Row {
                Text(text = it.author )
                Spacer(modifier = Modifier.width(10.dp))
                Text(text = it.content)
            }

        }
        messages.clear()
    }


}

}

data class Message(var author:String="",var content:String="")

(Edit)

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:

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