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/*
 * This library is part of OpenCms -
 * the Open Source Content Management System
 *
 * Copyright (C) Alkacon Software (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.ade.galleries.client.ui;

import org.opencms.ade.galleries.shared.CmsGallerySearchBean;
import org.opencms.ade.galleries.shared.CmsResultItemBean;

import java.util.List;

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;

/**
 * Scroll handler class which loads more items in the front of the search result list when the user scrolls to the
 * top.

*/ public class CmsResultsBackwardsScrollHandler implements ScrollHandler { /** The scroll threshold in pixels. */ public static final int SCROLL_THRESHOLD = 50; /** Flag used to temporarily disable the scroll handler. */ protected boolean m_enabled = true; /** The index of the first shown page. */ protected int m_firstShownPage; /** The number of results per page. */ protected int m_pageSize; /** The list of search result beans. */ protected List m_resultBeans; /** The search results tab. */ protected CmsResultsTab m_resultsTab; /** The search bean. */ protected CmsGallerySearchBean m_searchBean; /** * Creates a new handler instance for a given results tab.

* * @param resultsTab the results tab for which to create the handler */ public CmsResultsBackwardsScrollHandler(CmsResultsTab resultsTab) { m_resultsTab = resultsTab; } /** * Checks whether more items can be loaded at the front of the list.

* * @return true if more items can be loaded at the front of the list */ public boolean hasMore() { return m_firstShownPage > 1; } /** * @see com.google.gwt.event.dom.client.ScrollHandler#onScroll(com.google.gwt.event.dom.client.ScrollEvent) */ public void onScroll(ScrollEvent event) { if (m_searchBean == null) { return; } if (m_resultBeans == null) { return; } if (!m_enabled) { return; } final ScrollPanel scrollPanel = (ScrollPanel)event.getSource(); final int scrollPos = scrollPanel.getVerticalScrollPosition(); if ((scrollPos <= SCROLL_THRESHOLD) && hasMore()) { m_enabled = false; Scheduler.get().scheduleDeferred(new ScheduledCommand() { /** * @see com.google.gwt.core.client.Scheduler.ScheduledCommand#execute() */ public void execute() { m_enabled = true; m_resultsTab.getList().setVerticalScrollPosition(50); } }); loadPreviousPage(); } } /** * Updates the handler with a new search bean.

* * @param searchBean the search bean */ public void updateSearchBean(CmsGallerySearchBean searchBean) { m_searchBean = searchBean; if (searchBean != null) { m_pageSize = searchBean.getMatchesPerPage(); int lastPage = searchBean.getLastPage(); // we don't just store the search bean because it gets reused for multiple searches // and so the result list may change. m_resultBeans = searchBean.getResults(); if (lastPage != -1) { loadPage(lastPage); m_firstShownPage = lastPage; if (lastPage > 1) { loadPage(lastPage - 1); m_firstShownPage = lastPage - 1; } } } else { m_resultBeans = null; } } /** * Loads a page with a given index.

* * @param pageNum the index of the page to load */ protected void loadPage(int pageNum) { int start = (pageNum - 1) * m_pageSize; List results = m_resultBeans; int end = start + m_pageSize; if (end > results.size()) { end = results.size(); } List page = results.subList(start, end); m_resultsTab.addContentItems(page, true); } /** * Loads the page before the first shown page.

*/ protected void loadPreviousPage() { loadPage(m_firstShownPage - 1); m_firstShownPage -= 1; } }





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