    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.commons.util.AvailableValues;
    021import org.apache.tapestry5.commons.util.UnknownValueException;
    022import org.apache.tapestry5.ioc.annotations.Inject;
    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}