org.opencms.gwt.client.util.CmsScrollToBottomHandler Maven / Gradle / Ivy
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/*
* This library is part of OpenCms -
* the Open Source Content Management System
*
* Copyright (c) Alkacon Software GmbH (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;
}
});
}
}
}