DatabaseException: Can’t convert object of type java.lang.String to type

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 command in firebase comes from a separate software. The app is built on top of the Parrot Drone SDK Sample code.

It seems to be able to get the text from the command object and append it to a textview, but when a new child is added it just crashes. I’m getting this error when a new child is added.

E/AndroidRuntime: FATAL EXCEPTION: main
                Process: com.parrot.sdksample, PID: 10592
                com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.parrot.sdksample.activity.CommandObject
                    at com.google.android.gms.internal.zg.zzb(Unknown Source)
                    at com.google.android.gms.internal.zg.zza(Unknown Source)
                    at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
                    at com.parrot.sdksample.activity.MiniDroneActivity$13.onChildAdded(MiniDroneActivity.java:383)
                    at com.google.android.gms.internal.px.zza(Unknown Source)
                    at com.google.android.gms.internal.vj.zzHX(Unknown Source)
                    at com.google.android.gms.internal.vp.run(Unknown Source)
                    at android.os.Handler.handleCallback(Handler.java:739)
                    at android.os.Handler.dispatchMessage(Handler.java:95)
                    at android.os.Looper.loop(Looper.java:148)
                    at android.app.ActivityThread.main(ActivityThread.java:5417)
                    at java.lang.reflect.Method.invoke(Native Method)
                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

A sample of my data structure in firebase is below.

{
"drones" : {
    "commands" : {
    "-L-n9HwaQktOdI2VEVlH" : {
        "executed" : false,
        "text" : "TAKE_OFF",
        "timestamp" : 1.512686825309134E9
    },
    "-L-nAuK5Ifde7Cdnan8K" : {
        "executed" : false,
        "text" : "LAND",
        "timestamp" : 1.512687248764272E9
    }
    }
}
}

The function in my activity to get data from firebase looks like this.

private void initFirebase(){
        mCommandTextView = (TextView) findViewById(R.id.commandTextView);

        FirebaseDatabase database = FirebaseDatabase.getInstance();
        DatabaseReference commandsRef = database.getReference("drones/commands");

        ChildEventListener childEventListener = new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String previousChildName) {
                Log.d(TAG, "onChildAdded:" + dataSnapshot.getKey());
                CommandObject command = dataSnapshot.getValue(CommandObject.class);
                mCommandTextView.append(command.text + "n");
// I've tried commenting out the if statements below this, but it doesn't seem to make a difference.
                if ("TAKE_OFF".equals(command.text)) {
                    mMiniDrone.takeOff();
                } else if ("LAND".equals(command.text)) {
                    mMiniDrone.land();
                }
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String previousChildName){

            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

            }

            public void onChildMoved(DataSnapshot dataSnapshot, String previousChildName){

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        };
        commandsRef.addChildEventListener(childEventListener);
    }

My CommandObject class looks like this.

public class CommandObject {
    public String text;
    public float timestamp;
    public boolean executed;

    public CommandObject() {
    }

    public CommandObject(boolean executed, String text, float timestamp){
        this.executed = executed;
        this.text = text;
        this.timestamp = timestamp;
    }
}

I’ve also tried using a value event listener instead, but the same problem occured.