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Guise™ Internet application framework.
There is a newer version: 0.5.3
/*
 * Copyright © 2005-2008 GlobalMentor, Inc. 
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.guise.framework.component.layout;

import java.util.*;

import io.guise.framework.component.Component;

/**
 * A layout for components bound to component references such as IDs.
 * @author Garret Wilson
 */
public class ReferenceLayout extends AbstractLayout {

	/** The lazily-created map of components mapped to reference IDs. */
	private Map referenceIDComponentMap = null;

	/** @return The lazily-created map of components mapped to reference IDs. */
	protected Map getReferenceIDComponentMap() {
		if(referenceIDComponentMap == null) { //if the map hasn't been created, yet
			referenceIDComponentMap = new HashMap(); //create a new map
		}
		return referenceIDComponentMap; //return the map of components keyed to IDs
	}

	@Override
	public Class getConstraintsClass() {
		return ReferenceConstraints.class;
	}

	/**
	 * {@inheritDoc}
	 * 
	 * This version adds or removes the component reference ID to the map.
	 * 
	 */
	@Override
	protected void componentConstraintsChanged(final Component component, final Constraints oldConstraints, final Constraints newConstraints) {
		final Class constraintsClass = getConstraintsClass(); //get the type of constraints we expect
		if(constraintsClass.isInstance(oldConstraints)) { //if the old constraints is of the type of we expect
			getReferenceIDComponentMap().remove(constraintsClass.cast(oldConstraints).getID()); //remove the ID/component association from the map
		}
		if(constraintsClass.isInstance(newConstraints)) { //if the new constraints is of the type of we expect
			getReferenceIDComponentMap().put(constraintsClass.cast(newConstraints).getID(), component); //associate the component with the reference ID
		}
	}

	@Override
	public ReferenceConstraints createDefaultConstraints() {
		throw new IllegalStateException("Component cannot have default constraints; it must be bound to some ID.");
	}

	/**
	 * Retrieves a component bound to a given ID.
	 * @param id The ID with which a component may be bound.
	 * @return A component with constraints specifying the given ID, or null if there is no component bound to the given ID.
	 */
	public Component getComponentByID(final String id) {
		return getReferenceIDComponentMap().get(id); //look up the component by its reference ID
	}

}