001// Copyright 2009 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.tapestry5.corelib.base;
016
017import org.apache.tapestry5.BindingConstants;
018import org.apache.tapestry5.Block;
019import org.apache.tapestry5.ComponentResources;
020import org.apache.tapestry5.MarkupWriter;
021import org.apache.tapestry5.annotations.Parameter;
022import org.apache.tapestry5.annotations.SupportsInformalParameters;
023import org.apache.tapestry5.ioc.annotations.Inject;
024
025/**
026 * Base class for {@link org.apache.tapestry5.corelib.components.If} and {@link org.apache.tapestry5.corelib.components.Unless}.
027 * Will render its body or the block from its else parameter.  If it renders anything and it has an element name, then
028 * it renders the element and its informal parameters.
029 */
030@SupportsInformalParameters
031public abstract class AbstractConditional
032{
033    @Inject
034    private ComponentResources resources;
035
036    /**
037     * Performs the test via the parameters; return true to render the body of the component, false to render the else
038     * block (or nothing).
039     *
040     * @return true to render body
041     */
042    protected abstract boolean test();
043
044    /**
045     * An alternate {@link org.apache.tapestry5.Block} to render if {@link #test()} is false. The default, null, means
046     * render nothing in that situation.
047     */
048    @Parameter(name = "else", defaultPrefix = BindingConstants.LITERAL)
049    private Block elseBlock;
050
051    private boolean renderTag;
052
053    /**
054     * Returns null if the {@link #test()} is true, which allows normal rendering (of the body). If the test parameter
055     * is false, returns the else parameter (this may also be null).
056     */
057    Object beginRender(MarkupWriter writer)
058    {
059        Block toRender = test() ? resources.getBody() : elseBlock;
060
061        String elementName = resources.getElementName();
062
063        renderTag = toRender != null && elementName != null;
064
065        if (renderTag)
066        {
067            writer.element(elementName);
068            resources.renderInformalParameters(writer);
069        }
070
071        return toRender;
072    }
073
074    /**
075     * If {@link #test()} is true, then the body is rendered, otherwise not. The component does not have a template or
076     * do any other rendering besides its body.
077     */
078    boolean beforeRenderBody()
079    {
080        return false;
081    }
082
083    void afterRenderBody(MarkupWriter writer)
084    {
085        if (renderTag)
086            writer.end();
087    }
088
089
090}