| /******************************************************************************* |
| * Copyright (c) 2004, 2005 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.contexts; |
| |
| import java.util.HashSet; |
| import java.util.Iterator; |
| import java.util.Set; |
| |
| import org.eclipse.core.commands.common.NamedHandleObject; |
| import org.eclipse.core.commands.common.NotDefinedException; |
| import org.eclipse.core.internal.commands.util.Util; |
| |
| /** |
| * <p> |
| * A context is an answer to the question "when". Other services can listen for |
| * the activation and deactivation of contexts, and change their own state in |
| * response to these changes. For example, Eclipse's key binding service listens |
| * to context activation and deactivation to determine which key bindings should |
| * be active. |
| * </p> |
| * <p> |
| * An instance of this interface can be obtained from an instance of |
| * <code>ContextManager</code> for any identifier, whether or not an context |
| * with that identifier is defined in the extension registry. |
| * </p> |
| * <p> |
| * The handle-based nature of this API allows it to work well with runtime |
| * plugin activation and deactivation. If a context is defined, that means that |
| * its corresponding plug-in is active. If the plug-in is then deactivated, the |
| * context will still exist but it will be undefined. An attempts to use an |
| * undefined context will result in a <code>NotDefinedException</code> being |
| * thrown. |
| * </p> |
| * <p> |
| * This class is not intended to be extended by clients. |
| * </p> |
| * |
| * @since 3.1 |
| * @see ContextManager |
| */ |
| public final class Context extends NamedHandleObject implements Comparable { |
| |
| /** |
| * The collection of all objects listening to changes on this context. This |
| * value is <code>null</code> if there are no listeners. |
| */ |
| private Set listeners = null; |
| |
| /** |
| * The parent identifier for this context. The meaning of a parent is |
| * dependent on the system using contexts. This value can be |
| * <code>null</code> if the context has no parent. |
| */ |
| private String parentId = null; |
| |
| /** |
| * Constructs a new instance of <code>Context</code>. |
| * |
| * @param id |
| * The id for this context; must not be <code>null</code>. |
| */ |
| Context(final String id) { |
| super(id); |
| } |
| |
| /** |
| * Registers an instance of <code>IContextListener</code> to listen for |
| * changes to properties of this instance. |
| * |
| * @param listener |
| * the instance to register. Must not be <code>null</code>. If |
| * an attempt is made to register an instance which is already |
| * registered with this instance, no operation is performed. |
| */ |
| public final void addContextListener(final IContextListener listener) { |
| if (listener == null) { |
| throw new NullPointerException(); |
| } |
| |
| if (listeners == null) { |
| listeners = new HashSet(); |
| } |
| |
| listeners.add(listener); |
| } |
| |
| /* (non-Javadoc) |
| * @see java.lang.Comparable#compareTo(java.lang.Object) |
| */ |
| public final int compareTo(final Object object) { |
| final Context scheme = (Context) object; |
| int compareTo = Util.compare(this.id, scheme.id); |
| if (compareTo == 0) { |
| compareTo = Util.compare(this.name, scheme.name); |
| if (compareTo == 0) { |
| compareTo = Util.compare(this.parentId, scheme.parentId); |
| if (compareTo == 0) { |
| compareTo = Util.compare(this.description, |
| scheme.description); |
| if (compareTo == 0) { |
| compareTo = Util.compare(this.defined, scheme.defined); |
| } |
| } |
| } |
| } |
| |
| return compareTo; |
| } |
| |
| /** |
| * <p> |
| * Defines this context by giving it a name, and possibly a description and |
| * a parent identifier as well. The defined property automatically becomes |
| * <code>true</code>. |
| * </p> |
| * <p> |
| * Notification is sent to all listeners that something has changed. |
| * </p> |
| * |
| * @param name |
| * The name of this context; must not be <code>null</code>. |
| * @param description |
| * The description for this context; may be <code>null</code>. |
| * @param parentId |
| * The parent identifier for this context; may be |
| * <code>null</code>. |
| */ |
| public final void define(final String name, final String description, |
| final String parentId) { |
| if (name == null) { |
| throw new NullPointerException( |
| "The name of a scheme cannot be null"); //$NON-NLS-1$ |
| } |
| |
| final boolean definedChanged = !this.defined; |
| this.defined = true; |
| |
| final boolean nameChanged = !Util.equals(this.name, name); |
| this.name = name; |
| |
| final boolean descriptionChanged = !Util.equals(this.description, |
| description); |
| this.description = description; |
| |
| final boolean parentIdChanged = !Util.equals(this.parentId, parentId); |
| this.parentId = parentId; |
| |
| fireContextChanged(new ContextEvent(this, definedChanged, nameChanged, |
| descriptionChanged, parentIdChanged)); |
| } |
| |
| /** |
| * Notifies all listeners that this context has changed. This sends the |
| * given event to all of the listeners, if any. |
| * |
| * @param event |
| * The event to send to the listeners; must not be |
| * <code>null</code>. |
| */ |
| private final void fireContextChanged(final ContextEvent event) { |
| if (event == null) { |
| throw new NullPointerException( |
| "Cannot send a null event to listeners."); //$NON-NLS-1$ |
| } |
| |
| if (listeners == null) { |
| return; |
| } |
| |
| final Iterator listenerItr = listeners.iterator(); |
| while (listenerItr.hasNext()) { |
| final IContextListener listener = (IContextListener) listenerItr |
| .next(); |
| listener.contextChanged(event); |
| } |
| } |
| |
| /** |
| * Returns the identifier of the parent of this instance. |
| * <p> |
| * Notification is sent to all registered listeners if this property |
| * changes. |
| * </p> |
| * |
| * @return the identifier of the parent of this instance. May be |
| * <code>null</code>. |
| * @throws NotDefinedException |
| * if this instance is not defined. |
| */ |
| public final String getParentId() throws NotDefinedException { |
| if (!defined) { |
| throw new NotDefinedException( |
| "Cannot get the parent identifier from an undefined context."); //$NON-NLS-1$ |
| } |
| |
| return parentId; |
| } |
| |
| /** |
| * Unregisters an instance of <code>IContextListener</code> listening for |
| * changes to properties of this instance. |
| * |
| * @param contextListener |
| * the instance to unregister. Must not be <code>null</code>. |
| * If an attempt is made to unregister an instance which is not |
| * already registered with this instance, no operation is |
| * performed. |
| */ |
| public final void removeContextListener( |
| final IContextListener contextListener) { |
| if (contextListener == null) { |
| throw new NullPointerException("Cannot remove a null listener."); //$NON-NLS-1$ |
| } |
| |
| if (listeners == null) { |
| return; |
| } |
| |
| listeners.remove(contextListener); |
| |
| if (listeners.isEmpty()) { |
| listeners = null; |
| } |
| } |
| |
| /** |
| * The string representation of this context -- for debugging purposes only. |
| * This string should not be shown to an end user. |
| * |
| * @return The string representation; never <code>null</code>. |
| */ |
| public final String toString() { |
| if (string == null) { |
| final StringBuffer stringBuffer = new StringBuffer(); |
| stringBuffer.append("Context("); //$NON-NLS-1$ |
| stringBuffer.append(id); |
| stringBuffer.append(','); |
| stringBuffer.append(name); |
| stringBuffer.append(','); |
| stringBuffer.append(description); |
| stringBuffer.append(','); |
| stringBuffer.append(parentId); |
| stringBuffer.append(','); |
| stringBuffer.append(defined); |
| stringBuffer.append(')'); |
| string = stringBuffer.toString(); |
| } |
| return string; |
| } |
| |
| /** |
| * Makes this context become undefined. This has the side effect of changing |
| * the name, description and parent identifier to <code>null</code>. |
| * Notification is sent to all listeners. |
| */ |
| public final void undefine() { |
| string = null; |
| |
| final boolean definedChanged = defined; |
| defined = false; |
| |
| final boolean nameChanged = name != null; |
| name = null; |
| |
| final boolean descriptionChanged = description != null; |
| description = null; |
| |
| final boolean parentIdChanged = parentId != null; |
| parentId = null; |
| |
| fireContextChanged(new ContextEvent(this, definedChanged, nameChanged, |
| descriptionChanged, parentIdChanged)); |
| } |
| } |