Bindings.and() in JavaFX not firing? - javafx

Question

On startup my JavaFX app fires off two background tasks, one to initialize the database and the other to authenticate against an email server. Each task has a Boolean property indicating successful completion. Once both of those tasks complete I want to start a third task to start polling for new emails.
I thought I could use javafx.beans.binding.Bindings.and() to combine the result of these two tasks, but it's not firing. Here's some code:
BooleanBinding databaseInitializedProperty = NotesLocalDatabase.initializationStateProperty().isEqualTo( State.SUCCEEDED );
BooleanProperty isLoggedInProperty = loginPanel.isLoggedInProperty();
databaseInitializedProperty.addListener( (value, oldVal, newVal ) -> {
if( newVal ) log.info( "DATABASE INITIALIZED" ); } );
isLoggedInProperty.addListener( (value, oldVal, newVal ) -> {
if( newVal ) log.info( "IS LOGGED IN" ); } );
Bindings.and( databaseInitializedProperty, isLoggedInProperty ).addListener( (value, oldVal, newVal) -> {
log.info( "COMPOUND BINDING CHANGED: " + value + ", " + oldVal + ", " + newVal );
if( newVal ) {
log.info( "Login and database initialization both complete. Starting message check service." );
startUpdates();
}
} );
I know my properties are working correctly because I see both "DATABASE INITIALIZED" and "IS LOGGED IN" in the logs. However, I never see "COMPOUND BINDING CHANGED". From reading the docs I was under the impression that the change listener on Bindings.and() binding be fired whenever either property changes. Is that not the case?

Answer 1

You are running into another version of this: Bidirectional JavaFX Binding is destroyed by unrelated code
The problem is that the result of Bindings.and(...) has gone out of scope by the time the properties change. This makes it eligible for garbage collection. It's not unreasonable to assume your tasks are consuming enough memory to force the garbage collector to run, so the binding gets destroyed.
For a simple example, run the following with and without the call to System.gc();:
import javafx.beans.binding.Bindings;
import javafx.beans.property.BooleanProperty;
import javafx.beans.property.SimpleBooleanProperty;
public class BindingTest {
public static void main(String[] args) {
BooleanProperty x = new SimpleBooleanProperty(false);
BooleanProperty y = new SimpleBooleanProperty(false);
x.addListener((obs, oldX, newX) -> System.out.printf("x changed from %s to %s%n", oldX, newX));
y.addListener((obs, oldY, newY) -> System.out.printf("y changed from %s to %s%n", oldY, newY));
Bindings.and(x, y).addListener((obs, oldXAndY, newXAndY) -> System.out.printf("x&y changed from %s to %s%n", oldXAndY, newXAndY));
x.set(true);
// System.gc();
y.set(true);
}
}
The fix is to force the binding to stay in scope. You may need to (somewhat unnaturally) make it an instance variable somewhere:
public class SomeClass {
private BooleanBinding initializationComplete ;
public void whereverYouHadThisCodeBefore() {
// ..
initializationComplete = Bindings.and(databaseInitializedProperty, isLoggedInProperty);
initializationComplete.addListener(...);
}
}