org.eclipse.gmf.runtime.emf.type.core/src/org/eclipse/gmf/runtime/emf/type/core/NullElementType.java

/******************************************************************************
 * Copyright (c) 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.gmf.runtime.emf.type.core;

import org.eclipse.gmf.runtime.common.core.command.ICommand;
import org.eclipse.gmf.runtime.emf.type.core.edithelper.AbstractEditHelper;
import org.eclipse.gmf.runtime.emf.type.core.requests.IEditCommandRequest;

/**
 * Singleton element type that has no <code>EClass</code>. Clients can
 * specialized this element type if they wish to declare types that do not have
 * a matching <code>EClass</code>.
 * 
 * @author ldamus
 */
public class NullElementType
	extends MetamodelType {

	/**
	 * Edit helper for the NullElementType that considers before and after
	 * advice, only.
	 */
	private static class NullEditHelper
		extends AbstractEditHelper {

		protected ICommand getInsteadCommand(IEditCommandRequest req) {
			return null;
		}
	}

	/**
	 * The ID.
	 */
	public static final String ID = "org.eclipse.gmf.runtime.emf.type.core.null"; //$NON-NLS-1$

	/**
	 * The singleton instance.
	 */
	private static NullElementType _instance;

	/**
	 * Gets the singleton instance.
	 * 
	 * @return the singleton instance
	 */
	public static NullElementType getInstance() {
		if (_instance == null) {
			_instance = new NullElementType();
		}
		return _instance;
	}

	/**
	 * Private constructor.
	 */
	private NullElementType() {
		super(ID, null, null, null, new NullEditHelper());
	}

}