ConditionalListView.java

/**
 * Copyright 2013 55 Minutes (http://www.55minutes.com)
 *
 * 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 lt.inventi.wicket.component.repeater;

import java.util.List;

import org.apache.wicket.markup.html.list.ListView;
import org.apache.wicket.model.IModel;

/**
 * A {@link ListView} that returns <code>false</code> for {@link #isVisible} if
 * its list is empty. This allows you to use the
 * <code><wicket:enclosure></code> tag to hide surrounding markup.
 * Therefore you can use this component to ensure that, for example, the
 * <code><ul></code> is ommitted when you have zero
 * <code><li></code> elements.
 * <em>This is necessary for valid XHTML markup.</em>
 * <p>
 * Example usage:
 *
 * <pre class="example">
 * <wicket:enclosure child="item">
 *   <ul>
 *     <li wicket:id="item">...</li>
 *   </ul>
 * </wicket:enclosure>
 *
 * add(new ConditionalListView<Person>("people", personList) {
 *     @Override protected void populateItem(ListItem<Person> item)
 *     {
 *         item.add(...);
 *     }
 * });
 * </pre>
 * <p>
 * In this example, if the {@code personList} model is {@code null} or empty,
 * the entire enclosure will be omitted from the HTML output.
 */
public abstract class ConditionalListView<T> extends ListView<T>
{
    public ConditionalListView(String id) {
        super(id);
    }

    public ConditionalListView(String id, IModel<? extends List<? extends T>> model) {
        super(id, model);
    }

    public ConditionalListView(String id, List<? extends T> list) {
        super(id, list);
    }

    /**
     * Returns <code>false</code> if the list is empty.
     */
    @Override
    public boolean isVisible() {
        return getViewSize() > 0;
    }
}