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.util.Defense;
018    import org.apache.tapestry.AbstractComponent;
019    import org.apache.tapestry.IComponent;
020    import org.apache.tapestry.IMarkupWriter;
021    import org.apache.tapestry.IRequestCycle;
022    
023    /**
024     * Prevents its contents from being rendered until triggered by an {@link RenderBlock} component. [<a
025     * href="../../../../../ComponentReference/Block.html">Component Reference</a>]
026     * <p>
027     * Block and {@link RenderBlock} are used to build a certain class of complicated component that
028     * can't be assembled using the normal wrapping containment. Such a super component would have two
029     * or more sections that need to be supplied by the containing page (or component).
030     * <p>
031     * Using Blocks, the blocks can be provided as parameters to the super component.
032     * <p>
033     * The invoker property gives the components inside the block access to the component (typically an
034     * {@link RenderBlock}) that rendered the block. More often, the {@link #getParameter(String)}
035     * method is used to get parameters <em>of the invoking component</em>.
036     * 
037     * @author Howard Lewis Ship
038     * @since 0.2.9
039     */
040    
041    public abstract class Block extends AbstractComponent
042    {
043        private IComponent _invoker;
044    
045        /**
046         * Provides access to the invoking component's parameters.
047         * 
048         * @since 4.0
049         */
050    
051        public Object getParameter(String name)
052        {
053            return _invoker.getBinding(name).getObject();
054        }
055    
056        public void renderForComponent(IMarkupWriter writer, IRequestCycle cycle, IComponent invoker)
057        {
058            Defense.notNull(invoker, "invoker");
059    
060            IComponent oldInvoker = _invoker;
061    
062            try
063            {
064                _invoker = invoker;
065                renderBody(writer, cycle);
066            }
067            finally
068            {
069                _invoker = oldInvoker;
070    
071            }
072        }
073    
074        /**
075         * Does nothing; the idea of a Block is to defer the rendering of the body of the block until an
076         * {@link RenderBlock} forces it out.
077         */
078    
079        protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle)
080        {
081            // Nothing!
082        }
083    
084        /**
085         * Returns the object which invoked this Block's
086         * {@link #renderForComponent(IMarkupWriter, IRequestCycle, IComponent)} method. This is often
087         * used to access the informal parameters of a {@link RenderBlock} component.
088         * 
089         * @since 4.0
090         */
091        public IComponent getInvoker()
092        {
093            return _invoker;
094        }
095    
096        /**
097         * Used for testing only.
098         * 
099         * @since 4.0
100         */
101    
102        void setInvoker(IComponent invoker)
103        {
104            _invoker = invoker;
105        }
106    }