    001// Copyright 2011 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
    015package org.apache.tapestry5.corelib.components;
    016
    017import org.apache.tapestry5.BindingConstants;
    018import org.apache.tapestry5.Block;
    019import org.apache.tapestry5.ComponentResources;
    020import org.apache.tapestry5.annotations.Parameter;
    021import org.apache.tapestry5.annotations.SupportsInformalParameters;
    022import org.apache.tapestry5.ioc.annotations.Inject;
    023import org.apache.tapestry5.ioc.util.AvailableValues;
    024import org.apache.tapestry5.ioc.util.UnknownValueException;
    025import org.apache.tapestry5.runtime.RenderCommand;
    026import org.apache.tapestry5.services.dynamic.DynamicDelegate;
    027import org.apache.tapestry5.services.dynamic.DynamicTemplate;
    028import org.apache.tapestry5.services.dynamic.DynamicTemplateParser;
    029
    030/**
    031 * The Dynamic component allows a component to render itself differently at different times, by making use of
    032 * an external template file.
    033 * <p>
    034 * The content of the template file replaces the Dynamic component entirely with one exception: certain elements will be
    035 * replaced with {@linkplain Block}s passed to the Dynamic component as informal parameters; this is triggered by
    036 * <strong>id</strong> of the element. When the id attribute has the prefix {@code param:}, the remainder is the name of
    037 * a Block parameter. There are no limitations on what can appear inside such a Block: text, components, forms, even the
    038 * {@literal <t:body/>} directive.
    039 * <p>
    040 * Dynamic templates emulate how expansions work in standard Tapestry templates: Expansions (the <code>${ ... }</code>
    041 * syntax) can appear in attribute values or interspersed in element text. This allows container properties, messages,
    042 * assets, and so forth to be referenced within the external template. It should be noted that such access is quite a
    043 * bit less efficient than putting such expansions inside a referenced Block, but this should not be a big concern
    044 * outside of some kind of tight rendering loop.
    045 *
    046 * @since 5.3
    047 * @see DynamicTemplate
    048 * @see DynamicTemplateParser
    049 * @tapestrydoc
    050 */
    051@SupportsInformalParameters
    052public class Dynamic
    053{
    054    /** The dynamic template containing the content to be rendered by the component. */
    055    @Parameter(required = true, allowNull = false, defaultPrefix = BindingConstants.ASSET)
    056    private DynamicTemplate template;
    057
    058    @Inject
    059    private ComponentResources resources;
    060
    061    private final DynamicDelegate delegate = new DynamicDelegate()
    062    {
    063        public ComponentResources getComponentResources()
    064        {
    065            return resources;
    066        }
    067
    068        public Block getBlock(String name)
    069        {
    070            Block result = resources.getBlockParameter(name);
    071
    072            if (result != null)
    073                return result;
    074
    075            throw new UnknownValueException(String.format(
    076                    "Component %s does not have an informal Block parameter with id '%s'.", resources.getCompleteId(),
    077                    name), null, null, new AvailableValues("Available Blocks", resources.getInformalParameterNames()));
    078        }
    079    };
    080
    081    RenderCommand beginRender()
    082    {
    083        // Probably some room for caching here as well. It shouldn't be necessary to re-create the outermost
    084        // RenderCommand every time, unless the template has changed from the previous render.
    085        return template.createRenderCommand(delegate);
    086    }
    087}