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
015package org.apache.tapestry.event;
016
017import java.util.EventObject;
018
019import org.apache.hivemind.util.Defense;
020import org.apache.tapestry.IComponent;
021
022/**
023 * Event which describes a change to a particular {@link IComponent}.
024 * 
025 * @author Howard Ship
026 */
027
028public 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}