/*
* Copyright (c) 2011, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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package javafx.collections;
import javafx.beans.
NamedArg;
import javafx.beans.
WeakListener;
import java.lang.ref.
WeakReference;
/**
* A {@code WeakListChangeListener} can be used, if an {@link ObservableList}
* 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.
* <p>
* {@code WeakListChangeListener} are created by passing in the original
* {@link ListChangeListener}. The {@code WeakListChangeListener} should then be
* registered to listen for changes of the observed object.
* <p>
* Note: You have to keep a reference to the {@code ListChangeListener}, that
* was passed in as long as it is in use, otherwise it will be garbage collected
* to soon.
*
* @see ListChangeListener
* @see ObservableList
* @see javafx.beans.WeakListener
*
* @param <E>
* The type of the observed value
*
* @since JavaFX 2.1
*/
public final class
WeakListChangeListener<E> implements
ListChangeListener<E>,
WeakListener {
private final
WeakReference<
ListChangeListener<E>>
ref;
/**
* The constructor of {@code WeakListChangeListener}.
*
* @param listener
* The original listener that should be notified
*/
public
WeakListChangeListener(@
NamedArg("listener")
ListChangeListener<E>
listener) {
if (
listener == null) {
throw new
NullPointerException("Listener must be specified.");
}
this.
ref = new
WeakReference<
ListChangeListener<E>>(
listener);
}
/**
* {@inheritDoc}
*/
@
Override
public boolean
wasGarbageCollected() {
return (
ref.
get() == null);
}
/**
* {@inheritDoc}
*/
@
Override
public void
onChanged(
Change<? extends E>
change) {
final
ListChangeListener<E>
listener =
ref.
get();
if (
listener != null) {
listener.
onChanged(
change);
} else {
// The weakly reference listener has been garbage collected,
// so this WeakListener will now unhook itself from the
// source bean
change.
getList().
removeListener(this);
}
}
}