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.tapestry.AbstractComponent;
018    import org.apache.tapestry.IMarkupWriter;
019    import org.apache.tapestry.IRequestCycle;
020    
021    /**
022     * Renders the text and components wrapped by a {@link Block}component. [ <a
023     * href="../../../../../ComponentReference/RenderBlock.html">Component Reference
024     * </a>]
025     * <p>
026     * It is possible for an RenderBlock to obtain a Block from a page
027     * <em>other than</em> the render page. This works, even when the Block
028     * contains links, forms and form components. The action and direct services
029     * will create URLs that properly address this situation.
030     * <p>
031     * However, because the rendering page can't know ahead of time about these
032     * foreign Blocks, {@link org.apache.tapestry.event.PageBeginRenderListener} and
033     * {@link org.apache.tapestry.event.PageEndRenderListener} methods (for
034     * components and objects of the foreign page) via RenderBlock will <em>not</em>
035     * be executed. This specifically affects the methods of the
036     * {@link org.apache.tapestry.event.PageBeginRenderListener} and
037     * {@link org.apache.tapestry.event.PageEndRenderListener} interfaces.
038     * <p>
039     * Before rendering its {@link Block}, RenderBlock will set itself as the
040     * Block's inserter, and will reset the inserter after the {@link Block}is
041     * rendered. This gives the components contained in the {@link Block}access to
042     * its inserted environment via the RenderBlock. In particular this allows the
043     * contained components to access the informal parameters of the RenderBlock
044     * which effectively allows parameters to be passed to the components contained
045     * in a Block.
046     * 
047     * @author Howard Lewis Ship
048     */
049    
050    public abstract class RenderBlock extends AbstractComponent
051    {
052    
053        /**
054         * If block is not null, then
055         * {@link Block#renderForComponent(IMarkupWriter, IRequestCycle, IComponent)}
056         * is invoked.
057         */
058    
059        protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle)
060        {
061            Block block = getBlock();
062    
063            if (block == null) return;
064    
065            block.renderForComponent(writer, cycle, this);
066        }
067    
068        public abstract Block getBlock();
069    
070    }