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OpenCms is an enterprise-ready, easy to use website content management system based on Java and XML technology. Offering a complete set of features, OpenCms helps content managers worldwide to create and maintain beautiful websites fast and efficiently.

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/*
 * This library is part of OpenCms -
 * the Open Source Content Management System
 *
 * Copyright (c) Alkacon Software GmbH & Co. KG (http://www.alkacon.com)
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * For further information about Alkacon Software, please see the
 * company website: http://www.alkacon.com
 *
 * For further information about OpenCms, please see the
 * project website: http://www.opencms.org
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package org.opencms.gwt.client.util;

import com.google.gwt.core.client.Scheduler;
import com.google.gwt.core.client.Scheduler.ScheduledCommand;
import com.google.gwt.event.dom.client.ScrollEvent;
import com.google.gwt.event.dom.client.ScrollHandler;
import com.google.gwt.user.client.ui.ScrollPanel;
import com.google.gwt.user.client.ui.Widget;

/**
 * Scroll handler which executes an action when the user has scrolled to the bottom.

* * @since 8.0.0 */ public class CmsScrollToBottomHandler implements ScrollHandler { /** * If the lower edge of the content being scrolled is at most this many pixels below the lower * edge of the scrolling viewport, the action is triggered. */ public static final int DEFAULT_SCROLL_THRESHOLD = 30; /** * An internal flag that, if false, prevents the scroll action from being executed.

*/ protected boolean m_enabled = true; /** * The action which is triggered when the user scrolls to the bottom.

*/ private Runnable m_callback; /** * If the lower edge of the content being scrolled is at most this many pixels below the lower * edge of the scrolling viewport, the action is triggered. */ private int m_scrollThreshold = DEFAULT_SCROLL_THRESHOLD; /** * Constructs a new scroll handler.

* * @param callback the action which should be executed when the user scrolls to the bottom. */ public CmsScrollToBottomHandler(Runnable callback) { m_callback = callback; } /** * Constructs a new scroll handler with a custom scroll threshold. * * The scroll threshold is the distance from the bottom edge of the scrolled content * such that when the distance from the bottom edge of the scroll viewport to the bottom * edge of the scrolled content becomes lower than the distance, the scroll action is triggered. * * @param callback the action which should be executed when the user scrolls to the bottom. * @param scrollThreshold the scroll threshold */ public CmsScrollToBottomHandler(Runnable callback, int scrollThreshold) { m_callback = callback; m_scrollThreshold = scrollThreshold; } /** * @see com.google.gwt.event.dom.client.ScrollHandler#onScroll(com.google.gwt.event.dom.client.ScrollEvent) */ public void onScroll(ScrollEvent event) { if (!m_enabled) { return; } final ScrollPanel scrollPanel = (ScrollPanel)event.getSource(); final int scrollPos = scrollPanel.getVerticalScrollPosition(); Widget child = scrollPanel.getWidget(); int childHeight = child.getOffsetHeight(); int ownHeight = scrollPanel.getOffsetHeight(); boolean isBottom = (scrollPos + ownHeight) >= (childHeight - m_scrollThreshold); if (isBottom) { m_callback.run(); m_enabled = false; scrollPanel.setVerticalScrollPosition(scrollPos); Scheduler.get().scheduleDeferred(new ScheduledCommand() { /** * @see com.google.gwt.core.client.Scheduler.ScheduledCommand#execute() */ public void execute() { scrollPanel.setVerticalScrollPosition(scrollPos); m_enabled = true; } }); } } }





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