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* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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*
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package javafx.beans;
import java.lang.ref.WeakReference;
/**
* A {@code WeakInvalidationListener} can be used, if an {@link Observable}
* should only maintain a weak reference to the listener. This helps to avoid
* memory leaks, that can occur if observers are not unregistered from observed
* objects after use.
*
* {@code WeakInvalidationListener} are created by passing in the original
* {@link InvalidationListener}. The {@code WeakInvalidationListener} should
* then be registered to listen for changes of the observed object.
*
* Note: You have to keep a reference to the {@code InvalidationListener}, that
* was passed in as long as it is in use, otherwise it will be garbage collected
* to soon.
*
* @see InvalidationListener
* @see Observable
*
*
* @since JavaFX 2.0
*/
public final class WeakInvalidationListener implements InvalidationListener, WeakListener {
private final WeakReference ref;
/**
* The constructor of {@code WeakInvalidationListener}.
*
* @param listener
* The original listener that should be notified
*/
public WeakInvalidationListener(InvalidationListener listener) {
if (listener == null) {
throw new NullPointerException("Listener must be specified.");
}
this.ref = new WeakReference(listener);
}
/**
* {@inheritDoc}
*/
@Override
public boolean wasGarbageCollected() {
return (ref.get() == null);
}
/**
* {@inheritDoc}
*/
@Override
public void invalidated(Observable observable) {
InvalidationListener listener = ref.get();
if (listener != null) {
listener.invalidated(observable);
} else {
// The weakly reference listener has been garbage collected,
// so this WeakListener will now unhook itself from the
// source bean
observable.removeListener(this);
}
}
}