com.sun.javafx.binding.LazyObjectBinding Maven / Gradle / Ivy
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package com.sun.javafx.binding;
import javafx.beans.InvalidationListener;
import javafx.beans.binding.ObjectBinding;
import javafx.beans.value.ChangeListener;
import javafx.util.Subscription;
/**
* Extends {@link ObjectBinding} with the ability to lazily register and eagerly unregister listeners on its
* dependencies.
*
* @param the type of the wrapped {@code Object}
*/
abstract class LazyObjectBinding extends ObjectBinding {
private Subscription subscription;
private boolean wasObserved;
@Override
public void addListener(ChangeListener listener) {
super.addListener(listener);
updateSubscriptionAfterAdd();
}
@Override
public void removeListener(ChangeListener listener) {
super.removeListener(listener);
updateSubscriptionAfterRemove();
}
@Override
public void addListener(InvalidationListener listener) {
super.addListener(listener);
updateSubscriptionAfterAdd();
}
@Override
public void removeListener(InvalidationListener listener) {
super.removeListener(listener);
updateSubscriptionAfterRemove();
}
@Override
protected boolean allowValidation() {
return isObserved();
}
/**
* Called after a listener was added to start observing inputs if they're not observed already.
*/
private void updateSubscriptionAfterAdd() {
if (!wasObserved) { // was first observer registered?
subscription = observeSources(); // start observing source
wasObserved = true;
}
}
/**
* Called after a listener was removed to stop observing inputs if this was the last listener
* observing this binding.
*/
private void updateSubscriptionAfterRemove() {
if (wasObserved && !isObserved()) { // was last observer unregistered?
subscription.unsubscribe();
subscription = null;
invalidate(); // make binding invalid as source is no longer tracked
wasObserved = false;
}
}
/**
* Called when this binding was previously not observed and a new observer was added. Implementors must return a
* {@link Subscription} which will be cancelled when this binding no longer has any observers.
*
* @return a {@link Subscription} which will be cancelled when this binding no longer has any observers, never null
*/
protected abstract Subscription observeSources();
}