1 /* 2 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package javafx.beans; 27 28 import java.lang.ref.WeakReference; 29 import javafx.beans.NamedArg; 30 31 /** 32 * A {@code WeakInvalidationListener} can be used if an {@link Observable} 33 * should only maintain a weak reference to the listener. This helps to avoid 34 * memory leaks that can occur if observers are not unregistered from observed 35 * objects after use. 36 * <p> 37 * A {@code WeakInvalidationListener} is created by passing in the original 38 * {@link InvalidationListener}. The {@code WeakInvalidationListener} should 39 * then be registered to listen for changes of the observed object. 40 * <p> 41 * Note: You have to keep a reference to the {@code InvalidationListener} that 42 * was passed in as long as it is in use, otherwise it can be garbage collected 43 * too soon. 44 * 45 * @see InvalidationListener 46 * @see Observable 47 * 48 * 49 * @since JavaFX 2.0 50 */ 51 public final class WeakInvalidationListener implements InvalidationListener, WeakListener { 52 53 private final WeakReference<InvalidationListener> ref; 54 55 /** 56 * The constructor of {@code WeakInvalidationListener}. 57 * 58 * @param listener 59 * The original listener that should be notified 60 */ 61 public WeakInvalidationListener(@NamedArg("listener") InvalidationListener listener) { 62 if (listener == null) { 63 throw new NullPointerException("Listener must be specified."); 64 } 65 this.ref = new WeakReference<InvalidationListener>(listener); 66 } 67 68 /** 69 * {@inheritDoc} 70 */ 71 @Override 72 public boolean wasGarbageCollected() { 73 return (ref.get() == null); 74 } 75 76 /** 77 * {@inheritDoc} 78 */ 79 @Override 80 public void invalidated(Observable observable) { 81 InvalidationListener listener = ref.get(); 82 if (listener != null) { 83 listener.invalidated(observable); 84 } else { 85 // The weakly reference listener has been garbage collected, 86 // so this WeakListener will now unhook itself from the 87 // source bean 88 observable.removeListener(this); 89 } 90 } 91 }