ComponentEditPolicy.java

/*******************************************************************************
 * Copyright (c) 2000, 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.gef.editpolicies;

import org.eclipse.gef.Request;
import org.eclipse.gef.commands.Command;
import org.eclipse.gef.requests.GroupRequest;

/**
 * A model-based EditPolicy for <i>components within a </i>container</i>. A model-based
 * EditPolicy only knows about the host's model and the basic operations it supports. A
 * <i>component</i> is anything that is inside a container. By default,
 * ComponentEditPolicy understands being DELETEd from its container, and being ORPHANed
 * from its container. Subclasses can add support to handle additional behavior specific
 * to the model.
 * <P>ORPHAN is forwarded to the <i>parent</i> EditPart for it to handle.
 * <P>DELETE is also forwarded to the <i>parent</i> EditPart, but subclasses may also
 * contribute to the delete by overriding {@link #createDeleteCommand(GroupRequest)}.
 * <P>
 * This EditPolicy is not a {@link org.eclipse.gef.editpolicies.GraphicalEditPolicy}, and
 * should not be used to show feedback or interact with the host's visuals in any way.
 * <P>
 * This EditPolicy should not be used with {@link org.eclipse.gef.ConnectionEditPart}.
 * Connections do not really have a parent; use {@link ConnectionEditPolicy}.
 * @since 2.0
 */
public abstract class ComponentEditPolicy
	extends AbstractEditPolicy
{

/**
 * Override to contribute to the component's being deleted.
 * @param deleteRequest the DeleteRequest
 * @return Command <code>null</code> or a contribution to the delete
 */
protected Command createDeleteCommand(GroupRequest deleteRequest) {
	return null;
}

/**
 * Factors the incoming Request into ORPHANs and DELETEs.
 * @see org.eclipse.gef.EditPolicy#getCommand(Request)
 */
public Command getCommand(Request request) {
	if (REQ_ORPHAN.equals(request.getType()))
		return getOrphanCommand();
	if (REQ_DELETE.equals(request.getType()))
		return getDeleteCommand((GroupRequest)request);
	return null;
}

/**
 * Calls and returns {@link #createDeleteCommand(GroupRequest)}. This method is here for
 * historical reasons and used to perform additional function.
 * @param request the DeleteRequest
 * @return a delete command
 */
protected Command getDeleteCommand(GroupRequest request) {
	return createDeleteCommand(request);
}

/**
 * Returns the command contribution for orphaning this component from its container. By
 * default, ORPHAN is redispatched to the host's parent as an ORPHAN_CHILDREN Request. The
 * parents contribution is then returned.
 * @return the contribution obtained from the host's parent.
 */
protected Command getOrphanCommand() {
	GroupRequest req = new GroupRequest(REQ_ORPHAN_CHILDREN);
	req.setEditParts(getHost());
	return getHost().getParent().getCommand(req);
}

}