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.components;
016    
017    import org.apache.hivemind.HiveMind;
018    import org.apache.tapestry.AbstractComponent;
019    import org.apache.tapestry.IMarkupWriter;
020    import org.apache.tapestry.IRequestCycle;
021    
022    /**
023     * A conditional element on a page which will render its wrapped elements zero or one times. [ <a
024     * href="../../../../../ComponentReference/Conditional.html">Component Reference </a>]
025     * 
026     * @author Howard Lewis Ship, David Solis
027     */
028    
029    public abstract class Conditional extends AbstractComponent
030    {
031        /**
032         * Renders its wrapped components only if the condition is true (technically, if condition
033         * matches invert). Additionally, if element is specified, can emulate that HTML element if
034         * condition is met
035         */
036    
037        protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle)
038        {
039            if (evaluateCondition())
040            {
041                String element = getElement();
042    
043                boolean render = !cycle.isRewinding() && HiveMind.isNonBlank(element);
044    
045                if (render)
046                {
047                    writer.begin(element);
048                    renderInformalParameters(writer, cycle);
049                }
050    
051                renderBody(writer, cycle);
052    
053                if (render)
054                    writer.end(element);
055            }
056        }
057    
058        protected boolean evaluateCondition()
059        {
060            return getCondition() != getInvert();
061        }
062    
063        public abstract boolean getCondition();
064    
065        public abstract boolean getInvert();
066    
067        public abstract String getElement();
068    }