org.opencms.gwt.client.util.CmsFocusedScrollingHandler Maven / Gradle / Ivy
Show all versions of opencms-gwt Show documentation
/*
* 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.event.shared.HandlerRegistration;
import com.google.gwt.user.client.Event;
import com.google.gwt.user.client.Event.NativePreviewEvent;
import com.google.gwt.user.client.Event.NativePreviewHandler;
import com.google.gwt.user.client.ui.ScrollPanel;
import com.google.gwt.user.client.ui.Widget;
/**
* Native preview handler that focuses the on scroll wheel mouse event on the given scroll panel.
*/
public final class CmsFocusedScrollingHandler implements NativePreviewHandler {
/** The scroll panel. */
private ScrollPanel m_scrollPanel;
/** The scroll handler registration. */
private HandlerRegistration m_handlerRegistration;
/**
* Constructor.
*
* @param scrollPanel the scroll panel to focus on
*/
private CmsFocusedScrollingHandler(ScrollPanel scrollPanel) {
m_scrollPanel = scrollPanel;
}
/**
* Installs a focused scrolling handler on the given widget.
*
* @param scrollPanel the scroll panel
*
* @return the focused scrolling handler
*/
public static CmsFocusedScrollingHandler installFocusedScrollingHandler(ScrollPanel scrollPanel) {
if (scrollPanel == null) {
throw new UnsupportedOperationException("No scroll panel given");
}
CmsFocusedScrollingHandler handler = new CmsFocusedScrollingHandler(scrollPanel);
handler.register();
return handler;
}
/**
* @see com.google.gwt.user.client.Event.NativePreviewHandler#onPreviewNativeEvent(com.google.gwt.user.client.Event.NativePreviewEvent)
*/
public void onPreviewNativeEvent(NativePreviewEvent event) {
if ((Event.ONMOUSEWHEEL == event.getTypeInt()) && (m_handlerRegistration != null)) {
CmsPositionBean position = CmsPositionBean.generatePositionInfo(m_scrollPanel);
if (position.isOverElement(event.getNativeEvent().getClientX(), event.getNativeEvent().getClientY())) {
boolean cancelEvent = false;
int velocity = event.getNativeEvent().getMouseWheelVelocityY();
if (velocity > 0) {
Widget child = m_scrollPanel.getWidget();
int scrollSpace = child.getOffsetHeight()
- m_scrollPanel.getVerticalScrollPosition()
- m_scrollPanel.getOffsetHeight();
CmsDebugLog.getInstance().printLine("Scrolling down: " + scrollSpace);
cancelEvent = scrollSpace <= 0;
} else {
CmsDebugLog.getInstance().printLine("Scrolling up: " + m_scrollPanel.getVerticalScrollPosition());
cancelEvent = m_scrollPanel.getVerticalScrollPosition() == 0;
}
if (cancelEvent) {
event.cancel();
}
} else {
removeHandler();
}
}
}
/**
* Returns if the handler is currently registered.
*
* @return true if the handler is currently registered and active
*/
public boolean isRegistered() {
return m_handlerRegistration != null;
}
/**
* Registers the handler.
*/
public void register() {
removeHandler();
m_handlerRegistration = Event.addNativePreviewHandler(this);
}
/**
* Removes the handler and deactivates it.
* Call {@link #register()} the register again.
*/
public void removeHandler() {
if (m_handlerRegistration != null) {
m_handlerRegistration.removeHandler();
m_handlerRegistration = null;
}
}
}