Databaseexception: Can't Convert Object Of Type Java.lang.string To Type

December 13, 2023 Post a Comment

I've looked at a few other answers for similar problems but don't understand why mine isn't working. I'm trying to get my app to read commands from Firebase and move a drone. The c

Solution 1:

You are getting this error:

Can't convert object of typejava.lang.String to typecom.parrot.sdksample.activity.CommandObject

Because you are trying to read the data of type String which is of type CommandObject and that why you are getting this error.

A more simple way to get those values would be to use the String class like this:

DatabaseReferencerootRef= FirebaseDatabase.getInstance().getReference();
DatabaseReferencecommandsRef= rootRef.child("drones").child("commands");
ValueEventListenereventListener=newValueEventListener() {
    @OverridepublicvoidonDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            booleanexecuted= ds.child("executed").getValue(Boolean.class);
            Stringtext= ds.child("text").getValue(String.class);
            doubletimestamp= ds.child("timestamp").getValue(Double.class);
            Log.d("TAG", executed + " / " + text + " / " + timestamp);
        }
    }

    @OverridepublicvoidonCancelled(DatabaseError databaseError) {}
};
commandsRef.addListenerForSingleValueEvent(eventListener);

And this the approach using an object of CommandObject class:

DatabaseReferencerootRef= FirebaseDatabase.getInstance().getReference();
DatabaseReferencecommandsRef= rootRef.child("drones").child("commands");
ValueEventListenereventListener=newValueEventListener() {
    @OverridepublicvoidonDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            CommandObjectcommandObject= ds.getValue(CommandObject.class);
            Log.d("TAG", commandObject.getExecuted() + " / " + 
                commandObject.getText() + " / " + 
                commandObject.getTimestamp());
        }
    }

    @OverridepublicvoidonCancelled(DatabaseError databaseError) {}
};
commandsRef.addListenerForSingleValueEvent(eventListener);

In both cases your output will be:

false / TAKE_OFF / 1.512686825309134E9
false / LAND / 1.512687248764272E9

Solution 2:

The solution provided by Alex worked but didn't quite answer why I couldn't get store my data in an object, and for my app while the child added listener, the app is able to read data that was already on Firebase but when new child is added, the value is empty.

    onChildAdded:DataSnapshot { key = -L0JjGo-3QMYDsuTMQcN, value =  }

I've done a little more digging to find out what might be causing this and found that it is probably caused because the values were not all written at the same time. And looking at firebase it seems that the key is added first, then the values are added. This is why the error says can't convert, it is because it doesn't exist. I'm using the Python Firebase Admin SDK to add the data to Firebase, so I'm not sure if this is the reason for that.

So to fix my problem I moved my code to the onChildChanged function and added a check so that the code only runs when all of the data I need exists. This way I can get the values stored in an object straight away.

    @Override
    publicvoidonChildChanged(DataSnapshot dataSnapshot, String previousChildName){
        if (dataSnapshot.child("text").exists() &&
                dataSnapshot.child("executed").exists() &&
                dataSnapshot.child("timestamp").exists()){
            Log.d(TAG, "onChildChanged:" + dataSnapshot.toString());
            CommandObject command = dataSnapshot.getValue(CommandObject.class);
            if ("TAKE_OFF".equals(command.text)) {
                mMiniDrone.takeOff();
            } elseif ("LAND".equals(command.text)) {
                mMiniDrone.land();
            }
        }
    }

Solution 3:

Alex posted the right solution for me, but since I was using firebase-ui and kotlin, the code used is different. More info here

Baca Juga

val options = FirebaseRecyclerOptions.Builder<ChatMessage>()
            .setQuery(query, ChatMessage::class.java)
            .build()

    // equivalent options object with manual parsing, use it to debug which field gives errorval options = FirebaseRecyclerOptions.Builder<ChatMessage>()
            .setQuery(query, object : SnapshotParser<ChatMessage> {

                overridefunparseSnapshot(snapshot: DataSnapshot): ChatMessage {

                    val senderId = snapshot.child("senderId").getValue(String::class.java)
                    val receiverId = snapshot.child("receiverId").getValue(String::class.java)
                    val senderName = snapshot.child("senderName").getValue(String::class.java)
                    val text = snapshot.child("text").getValue(String::class.java)
                    val timestamp = snapshot.child("timestamp").getValue(Long::class.java)

                    return ChatMessage(senderId, receiverId, senderName, text, timestamp)
                }

            })
            .build()


    adapterMessages = object : FirebaseRecyclerAdapter<ChatMessage, ChatHolder>(options) {

        overridefunonCreateViewHolder(parent: ViewGroup, viewType: Int): ChatHolder {

            val rootView = LayoutInflater.from(parent.context).inflate(R.layout.chat_message_item, parent, false)

            return ChatHolder(rootView)
        }

        overridefunonBindViewHolder(holder: ChatHolder, position: Int, model: ChatMessage) {

            holder.populateItem(model)
        }
    }

Solution 4:

if u are using map object in your database should use get method directly with your object

doc: DocumentSnapshot val data = doc.get("location", SaleLocations::class.java)

Solution 5:

I faced a similar issue where I could not retrieve the data from the database; having a DatabaseException error with a message

can't convert from this type to that type.

The mistake I was making was I was writing incorrectly to the database. I wrote something like ...

mdatabaseReference.setValue(myObject)

instead of

mdatabaseReference.child(myObject.getId()).setValue(myObject)

So essentially the answer I am suggesting is: you should ensure your data is written correctly to the database at the right node in the JSON tree if not you would likely get this kind of error when you are reading from the database.

accessories-cc4u