Changing JavaFX nodes in Firebase onDataChange not working - firebase

Question

I'm working on a JavaFX admin application that works with Firebase Realtime Database. I've created a ValueEventListener that acquires the data I need in onDataChange. With this data I want to call a call a method that does something with this data. The problem I ran into is that changing JavaFX elements from inside this onDataChange method isn't working at all.
I've tried narrowing the problem down by putting everything in one class and put all the functionality in the onDataChange method, but that wouldn't work either.
What's confusing me the most about this is that reading these elements is working just fine, while changing them doesn't result in anything. It does work when I execute this code from outside onDataChange.
Code in database helper class:
public void startDropsListener() {
dropsRef.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
OverviewController.getInstance().changeNodes();
}
#Override
public void onCancelled(DatabaseError databaseError) {
System.out.println("Reading from database failed: " + databaseError.getCode());
}
});
}
Method for changing nodes:
public void changeNodes() {
System.out.println(title.getText()); // This does return the node's text.
title.setText("New title"); // Does not update the node's text.
}
UPDATE:
Printing the title after changing seems to be working, so the value appears to update despite it not showing. Here's the instance related code in case that might be the issue:
private static OverviewController instance;
public OverviewController() {
instance = this;
}
public static OverviewController getInstance() {
if(instance == null){
instance = new OverviewController();
}
return instance;
}

Answer 1

Don't make the controller a singleton.
and do like this...
public class OverviewController implements Initializable{
#FXML
public Label label;
#Override
public void initialize(URL location, ResourceBundle bundle){
DatabaseReference dropsRef = FirbaseDatabase.DatabaseReference("Node");
dropsRef.addValueEventListener(valueEventListener);
}
ValueEventListener valueEventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
Plateform.runLater(()->label.setText(dataSnashot.getValue(SomeClass.class).getLabel());
}
#Override
public void onCancelled(DatabaseError databaseError) {
System.out.println("Reading from database failed: " + databaseError.getCode());
}
});
}