| /******************************************************************************* |
| * Copyright (c) 2005, 2016 IBM Corporation and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License v1.0 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/epl-v10.html |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| *******************************************************************************/ |
| |
| package org.eclipse.core.commands.common; |
| |
| import org.eclipse.core.runtime.ListenerList; |
| |
| /** |
| * <p> |
| * A manager to which listeners can be attached. This handles the management of |
| * a list of listeners -- optimizing memory and performance. All the methods on |
| * this class are guaranteed to be thread-safe. |
| * </p> |
| * <p> |
| * Clients may extend. |
| * </p> |
| * <p> |
| * <b>Warning:</b> Do not use this class! Use {@link ListenerList} directly. See |
| * <a href="https://bugs.eclipse.org/486067">bug 486067</a>. |
| * </p> |
| * |
| * @since 3.2 |
| */ |
| public abstract class EventManager { |
| |
| /** |
| * An empty array that can be returned from a call to |
| * {@link #getListeners()} when {@link #listenerList} is <code>null</code>. |
| */ |
| private static final Object[] EMPTY_ARRAY = new Object[0]; |
| |
| /** |
| * A collection of objects listening to changes to this manager. This |
| * collection is <code>null</code> if there are no listeners. |
| */ |
| private volatile ListenerList<Object> listenerList = null; |
| |
| /** |
| * Adds a listener to this manager that will be notified when this manager's |
| * state changes. |
| * |
| * @param listener |
| * The listener to be added; must not be <code>null</code>. |
| */ |
| protected synchronized final void addListenerObject(final Object listener) { |
| if (listenerList == null) { |
| listenerList = new ListenerList<>(ListenerList.IDENTITY); |
| } |
| |
| listenerList.add(listener); |
| } |
| |
| /** |
| * Clears all of the listeners from the listener list. |
| */ |
| protected final void clearListeners() { |
| listenerList = null; |
| } |
| |
| /** |
| * Returns an array containing all the listeners attached to this event |
| * manager. The resulting array is unaffected by subsequent adds or removes. |
| * If there are no listeners registered, the result is an empty array. Use |
| * this method when notifying listeners, so that any modifications to the |
| * listener list during the notification will have no effect on the |
| * notification itself. |
| * <p> |
| * Note: Callers of this method <b>must not</b> modify the returned array. |
| * </p> |
| * |
| * @return The listeners currently attached; may be empty, but never |
| * <code>null</code> |
| */ |
| protected final Object[] getListeners() { |
| final ListenerList<Object> list = listenerList; |
| if (list == null) { |
| return EMPTY_ARRAY; |
| } |
| |
| return list.getListeners(); |
| } |
| |
| /** |
| * Whether one or more listeners are attached to the manager. |
| * |
| * @return <code>true</code> if listeners are attached to the manager; |
| * <code>false</code> otherwise. |
| */ |
| protected final boolean isListenerAttached() { |
| return listenerList != null; |
| } |
| |
| /** |
| * Removes a listener from this manager. Has no effect if the same listener |
| * was not already registered. |
| * |
| * @param listener |
| * The listener to be removed; must not be <code>null</code>. |
| */ |
| protected synchronized final void removeListenerObject(final Object listener) { |
| if (listener == null) { |
| throw new IllegalArgumentException(); |
| } |
| |
| if (listenerList != null) { |
| listenerList.remove(listener); |
| |
| if (listenerList.isEmpty()) { |
| listenerList = null; |
| } |
| } |
| } |
| } |