org.opencms.ade.galleries.client.ui.CmsResultsBackwardsScrollHandler Maven / Gradle / Ivy
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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 org.opencms.ade.galleries.shared.I_CmsGalleryProviderConstants.SortParams;
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);
boolean showPath = SortParams.path_asc.name().equals(m_searchBean.getSortOrder())
|| SortParams.path_desc.name().equals(m_searchBean.getSortOrder());
m_resultsTab.addContentItems(page, true, showPath);
}
/**
* Loads the page before the first shown page.
*/
protected void loadPreviousPage() {
loadPage(m_firstShownPage - 1);
m_firstShownPage -= 1;
}
}