001    // Copyright 2004, 2005 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry.event;
016    
017    import java.util.EventObject;
018    
019    import org.apache.hivemind.util.Defense;
020    import org.apache.tapestry.IComponent;
021    
022    /**
023     * Event which describes a change to a particular {@link IComponent}.
024     * 
025     * @author Howard Ship
026     */
027    
028    public class ObservedChangeEvent extends EventObject
029    {
030        private static final long serialVersionUID = -7693394232554811975L;
031    
032            private IComponent _component;
033    
034        private String _propertyName;
035    
036        private Object _newValue;
037    
038        /**
039         * Creates the event. The new value must be null, or be a serializable object. (It is declared
040         * as Object as a concession to the Java 2 collections framework, where the implementations are
041         * serializable but the interfaces (Map, List, etc.) don't extend Serializable ... so we wait
042         * until runtime to check).
043         * 
044         * @param component
045         *            The component (not necessarily a page) whose property changed.
046         * @param propertyName
047         *            the name of the property which was changed.
048         * @param newValue
049         *            The new value of the property.
050         * @throws IllegalArgumentException
051         *             if propertyName is null, or if the new value is not serializable
052         */
053    
054        public ObservedChangeEvent(IComponent component, String propertyName, Object newValue)
055        {
056            super(component);
057    
058            Defense.notNull(propertyName, "propertyName");
059    
060            _component = component;
061            _propertyName = propertyName;
062            _newValue = newValue;
063        }
064    
065        public IComponent getComponent()
066        {
067            return _component;
068        }
069    
070        public Object getNewValue()
071        {
072            return _newValue;
073        }
074    
075        public String getPropertyName()
076        {
077            return _propertyName;
078        }
079    
080    }