EmptyContainer.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.Collection;

import org.apache.wicket.markup.html.WebMarkupContainer;
import org.apache.wicket.model.IModel;
import org.apache.wicket.util.string.Strings;

/**
 * A WebMarkupContainer that is visible only if its model object is empty. This
 * is useful for displaying a conditional message when an accompanying list view
 * is empty.
 * <p>
 * For example:
 *
 * <pre class="example">
 * <wicket:enclosure>
 *   <ul>
 *     <li wicket:id="friends">...</li>
 *   </ul>
 * </wicket:enclosure>
 * <p wicket:id="no-friends">
 *   Your friends list is empty.
 * </p>
 * </pre>
 *
 * <pre class="example">
 * IModel<List<Friend>> friendsModel = ...;
 * add(new ConditionalListView("friends", friendsModel) {
 *     @Override
 *     protected void populateItem(ListItem<Friend> item)
 *     {
 *         ...
 *     }
 * });
 * // This will be visible only when friendsModel is empty
 * add(new EmptyContainer("no-friends", friendsModel));
 * </pre>
 *
 * @since 2.0
 */
public class EmptyContainer extends WebMarkupContainer {
    /**
     * Constructor with an implied model.
     */
    public EmptyContainer(String id) {
        super(id);
    }

    /**
     * Constructor with an explicit model.
     */
    public EmptyContainer(String id, IModel<?> model) {
        super(id, model);
    }

    /**
     * Returns {@code true} if the model object of this component is empty.
     */
    public boolean isModelEmpty() {
        return empty(getDefaultModelObject());
    }

    /**
     * Sets the visibility of this component to {@code true} if
     * {@link #isModelEmpty} returns {@code true}. Otherwise sets visibility to
     * {@code false}.
     */
    @Override
    protected void onConfigure() {
        super.onConfigure();
        setVisible(isModelEmpty());
    }

    private static boolean empty(Object obj) {
        boolean empty = false;
        if (null == obj) {
            empty = true;
        } else if (obj instanceof Boolean) {
            empty = !(Boolean) obj;
        } else if (obj instanceof Collection) {
            empty = ((Collection<?>) obj).size() == 0;
        } else if (obj instanceof String) {
            empty = Strings.isEmpty((String) obj);
        } else if (obj.getClass().isArray()) {
            empty = ((Object[]) obj).length == 0;
        }
        return empty;
    }

}