/* Columns.java{{IS_NOTE	Purpose:			Description:			History:		Tue Oct 25 16:00:29     2005, Created by tomyeh}}IS_NOTECopyright (C) 2005 Potix Corporation. All Rights Reserved.{{IS_RIGHT	This program is distributed under GPL Version 2.0 in the hope that	it will be useful, but WITHOUT ANY WARRANTY.}}IS_RIGHT*/package org.zkoss.zul;import org.zkoss.zk.ui.Component;import org.zkoss.zk.ui.UiException;import org.zkoss.zul.impl.HeadersElement;/** * Defines the columns of a grid. * Each child of a columns element should be a {@link Column} element. * * @author tomyeh */public class Columns extends HeadersElement {	//-- Component --//	public void setParent(Component parent) {		if (parent != null && !(parent instanceof Grid))			throw new UiException("Unsupported parent for columns: "+parent);		final boolean changed = getParent() != parent;		super.setParent(parent);		if (changed && parent != null) ((Grid)parent).initAtClient();	}	public boolean insertBefore(Component child, Component insertBefore) {		if (!(child instanceof Column))			throw new UiException("Unsupported child for columns: "+child);		if (super.insertBefore(child, insertBefore)) {			final Component parent = getParent();			if (parent != null) parent.invalidate();				//FUTURE: optimize the invalidation to attributes of				//certain cells				//It implies initAtClient			return true;		}		return false;	}	public boolean removeChild(Component child) {		if (super.removeChild(child)) {			final Component parent = getParent();			if (parent != null) parent.invalidate();				//FUTURE: optimize the invalidation to attributes of				//certain cells				//It implies initAtClient			return true;		}		return false;	}}