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.components;
016
017import org.apache.hivemind.HiveMind;
018import org.apache.tapestry.AbstractComponent;
019import org.apache.tapestry.IMarkupWriter;
020import 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
029public 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}