001// Licensed under the Apache License, Version 2.0 (the "License");
002// you may not use this file except in compliance with the License.
003// You may obtain a copy of the License at
004//
005// http://www.apache.org/licenses/LICENSE-2.0
006//
007// Unless required by applicable law or agreed to in writing, software
008// distributed under the License is distributed on an "AS IS" BASIS,
009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
010// See the License for the specific language governing permissions and
011// limitations under the License.
012
013package org.apache.tapestry5.corelib.components;
014
015import org.apache.tapestry5.BindingConstants;
016import org.apache.tapestry5.Block;
017import org.apache.tapestry5.ComponentResources;
018import org.apache.tapestry5.annotations.Parameter;
019import org.apache.tapestry5.annotations.SupportsInformalParameters;
020import org.apache.tapestry5.ioc.annotations.Inject;
021import org.apache.tapestry5.ioc.util.AvailableValues;
022import org.apache.tapestry5.ioc.util.UnknownValueException;
023import org.apache.tapestry5.runtime.RenderCommand;
024import org.apache.tapestry5.services.dynamic.DynamicDelegate;
025import org.apache.tapestry5.services.dynamic.DynamicTemplate;
026import org.apache.tapestry5.services.dynamic.DynamicTemplateParser;
027
028/**
029 * The Dynamic component allows a component to render itself differently at different times, by making use of
030 * an external template file.
031 *
032 * The content of the template file replaces the Dynamic component entirely with one exception: certain elements will be
033 * replaced with {@linkplain Block}s passed to the Dynamic component as informal parameters; this is triggered by
034 * <strong>id</strong> of the element. When the id attribute has the prefix {@code param:}, the remainder is the name of
035 * a Block parameter. There are no limitations on what can appear inside such a Block: text, components, forms, even the
036 * {@literal <t:body/>} directive.
037 *
038 * Dynamic templates emulate how expansions work in standard Tapestry templates: Expansions (the <code>${ ... }</code>
039 * syntax) can appear in attribute values or interspersed in element text. This allows container properties, messages,
040 * assets, and so forth to be referenced within the external template. It should be noted that such access is quite a
041 * bit less efficient than putting such expansions inside a referenced Block, but this should not be a big concern
042 * outside of some kind of tight rendering loop.
043 * 
044 * @since 5.3
045 * @see DynamicTemplate
046 * @see DynamicTemplateParser
047 * @tapestrydoc
048 */
049@SupportsInformalParameters
050public class Dynamic
051{
052    /** The dynamic template containing the content to be rendered by the component. */
053    @Parameter(required = true, allowNull = false, defaultPrefix = BindingConstants.ASSET)
054    private DynamicTemplate template;
055
056    @Inject
057    private ComponentResources resources;
058
059    private final DynamicDelegate delegate = new DynamicDelegate()
060    {
061        public ComponentResources getComponentResources()
062        {
063            return resources;
064        }
065
066        public Block getBlock(String name)
067        {
068            Block result = resources.getBlockParameter(name);
069
070            if (result != null)
071                return result;
072
073            throw new UnknownValueException(String.format(
074                    "Component %s does not have an informal Block parameter with id '%s'.", resources.getCompleteId(),
075                    name), null, null, new AvailableValues("Available Blocks", resources.getInformalParameterNames()));
076        }
077    };
078
079    RenderCommand beginRender()
080    {
081        // Probably some room for caching here as well. It shouldn't be necessary to re-create the outermost
082        // RenderCommand every time, unless the template has changed from the previous render.
083        return template.createRenderCommand(delegate);
084    }
085}