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. 024 * 025 * @author Howard Lewis Ship, David Solis 026 */ 027 028 public abstract class Conditional extends AbstractComponent 029 { 030 /** 031 * Renders its wrapped components only if the condition is true (technically, if condition 032 * matches invert). Additionally, if element is specified, can emulate that HTML element if 033 * condition is met 034 */ 035 036 protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle) 037 { 038 if (evaluateCondition()) 039 { 040 String element = getElement(); 041 042 boolean render = !cycle.isRewinding() && HiveMind.isNonBlank(element); 043 044 if (render) 045 { 046 writer.begin(element); 047 renderInformalParameters(writer, cycle); 048 } 049 050 renderBody(writer, cycle); 051 052 if (render) 053 writer.end(element); 054 } 055 } 056 057 protected boolean evaluateCondition() 058 { 059 return getCondition() != getInvert(); 060 } 061 062 public abstract boolean getCondition(); 063 064 public abstract boolean getInvert(); 065 066 public abstract String getElement(); 067 }