wicket-examples/src/java/wicket/examples/displaytag/list/SortableListViewHeader.java

/*
 * $Id$
 * $Revision$
 * $Date$
 *
 * ====================================================================
 * 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 wicket.examples.displaytag.list;

import java.util.Collections;
import java.util.Comparator;

import wicket.markup.ComponentTag;
import wicket.markup.html.border.Border;
import wicket.markup.html.link.Link;


/**
 * Sortable list view header component for a single list view column. Functionality provided
 * includes sorting the underlying list view and changing the colours (style) of the header.
 * @see SortableListViewHeaderGroup
 * @see SortableListViewHeaders
 * @author Juergen Donnerstag
 */
public abstract class SortableListViewHeader extends Border
{
	/** Sort ascending or descending */
	private boolean ascending;
	
	/** All sortable columns of a single list view are grouped */
	private final SortableListViewHeaderGroup group;

	/**
	 * Construct.
	 * @param id The component's id
	 * @param group The group of headers the new one will be added to
	 */
	public SortableListViewHeader(final String id, final SortableListViewHeaderGroup group)
	{
		super(id);

		// Default to descending.
		this.ascending = false;
		this.group = group;

		// If user clicks on the header, sorting will reverse
		add(new Link("actionLink")
		{
			public void onClick()
			{
				// call SortableTableHeaders implementation
				SortableListViewHeader.this.linkClicked();
			}
		});
	}

	/**
	 * Compare two objects (list elements of list view's model object). Both objects must
	 * implement Comparable. In order to compare basic types like int or double, simply
	 * subclass the method.
	 * @param o1 first object
	 * @param o2 second object
	 * @return comparision result
	 */
	protected int compareTo(Object o1, Object o2)
	{
		Comparable obj1 = getObjectToCompare(o1);
		Comparable obj2 = getObjectToCompare(o2);
		return obj1.compareTo(obj2);
	}

	/**
	 * Get CSS style for the header based on ascending / descending. Delegate to the header
	 * group to determine the style.
	 * @return css class
	 */
	protected final String getCssClass()
	{
		// TODO This needs to be integrated with our CSS design
		return group.getCssClass(getId(), ascending);
	}

	/**
	 * Returns the comparable object of the list view the header/column is referring to, e.g.
	 * obj.getId();
	 * @param object the ListItems model object
	 * @return The object to compare
	 */
	protected Comparable getObjectToCompare(Object object)
	{
		return (Comparable)object;
	}

	/**
	 * Header has been clicked. Define what to do.
	 */
	protected void linkClicked()
	{
		// change sorting order: ascending <-> descending
		ascending = !ascending;

		// Tell the header group that something has changed
		group.setSortedColumn(getId());

		// sort the list view's model data accordingly
		sort();
	}

	/**
	 * Delegate to the header group to handle the tag.
	 * @see wicket.Component#onComponentTag(wicket.markup.ComponentTag)
	 * @param tag The current ComponentTag to handle
	 */
	protected void onComponentTag(final ComponentTag tag)
	{
		group.handleComponentTag(tag, getCssClass());
	}

	/**
	 * Sort list view's model object based on column data
	 */
	protected void sort()
	{
		Collections.sort(group.getListViewModelObject(), new Comparator()
		{
			public int compare(Object o1, Object o2)
			{
				if (ascending)
				{
					return compareTo(o1, o2);
				}
				else
				{
					return compareTo(o2, o1);
				}
			}
		});
	}
}