tapestry-framework/src/org/apache/tapestry/components/RenderBlock.java

//  Copyright 2004 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package org.apache.tapestry.components;

import org.apache.tapestry.AbstractComponent;
import org.apache.tapestry.IComponent;
import org.apache.tapestry.IMarkupWriter;
import org.apache.tapestry.IRequestCycle;

/**
 *  Renders the text and components wrapped by a {@link Block} component.
 *
 *  [<a href="../../../../../ComponentReference/RenderBlock.html">Component Reference</a>]
 *
 *  <p>It is possible for an RenderBlock to obtain a Block
 *  from a page <em>other than</em> the render page.  This works, even when
 *  the Block contains links, forms and form components.  The action and
 *  direct services will create URLs that properly address this situation.
 *
 *  <p>However, because the rendering page can't know
 *  ahead of time about these foriegn Blocks,
 *  {@link org.apache.tapestry.event.PageRenderListener} methods
 *  (for components and objects of the foriegn page)
 *  via RenderBlock will <em>not</em> be executed.  This specifically
 *  affects the methods of the {@link org.apache.tapestry.event.PageRenderListener} 
 *  interface.
 * 
 *  <p>Before rendering its {@link Block}, RenderBlock will set itself as the 
 *  Block's inserter, and will reset the inserter after the {@link Block} is 
 *  rendered.  This gives the components contained in the {@link Block} access
 *  to its inserted environment via the RenderBlock.  In particular this allows
 *  the contained components to access the informal parameters of the RenderBlock
 *  which effectively allows parameters to be passed to the components contained
 *  in a Block.
 *
 * @author Howard Lewis Ship
 * @version $Id$
 * 
 **/

public abstract class RenderBlock extends AbstractComponent
{
    /**
     *  If block is not null,
     *  then the block's inserter is set (to this),
     * {@link org.apache.tapestry.IComponent#renderBody(IMarkupWriter, IRequestCycle)}
     *  is invoked on it, and the Block's inserter is set back to its previous state.
     *
     **/

    protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle)
    {
    	Block block = getBlock();
    	
        if (block != null)
        {
            // make a copy of the inserter so we don't overwrite completely
            IComponent previousInserter = block.getInserter();
            block.setInserter(this);
            block.renderBody(writer, cycle);
            // reset the inserter as it was before we changed it
            block.setInserter(previousInserter);
        }
    }

    public abstract Block getBlock();

}