    001// Copyright 2010-2013 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.ComponentResources;
    019import org.apache.tapestry5.Field;
    020import org.apache.tapestry5.MarkupWriter;
    021import org.apache.tapestry5.annotations.HeartbeatDeferred;
    022import org.apache.tapestry5.annotations.Parameter;
    023import org.apache.tapestry5.annotations.SupportsInformalParameters;
    024import org.apache.tapestry5.dom.Element;
    025import org.apache.tapestry5.ioc.annotations.Inject;
    026
    027/**
    028 * Provides a client-side element to contain validation errors; this renders as a {@code <p class="help-block">}.
    029 * Must be enclosed by a
    030 * {@link org.apache.tapestry5.corelib.components.Form} component and assumes the field and the Error component
    031 * are enclosed by a {@code <div class="form-group">}.
    032 * <p/>
    033 * It is acceptable to include multiple Errors components for a single field; this is sometimes necessary
    034 * when creating a responsive layout - which should probably ensure that only one of the Errors is
    035 * visible at any time.
    036 * <p/>
    037 * Errors is optional, and Tapestry's client-side logic will do a reasonable job of placing a help block
    038 * dynamically when a validation error must be presented; this component is intended for use when the default logic
    039 * doesn't place the help block in the right spot.
    040 *
    041 * @tapestrydoc
    042 * @since 5.2.0
    043 */
    044@SupportsInformalParameters
    045public class Error
    046{
    047    /**
    048     * The for parameter is used to identify the {@link Field} to present errors of.
    049     */
    050    @Parameter(name = "for", required = true, allowNull = false, defaultPrefix = BindingConstants.COMPONENT)
    051    private Field field;
    052
    053    @Inject
    054    private ComponentResources resources;
    055
    056    boolean beginRender(final MarkupWriter writer)
    057    {
    058        // Initially invisible; will be shown on client if an error exists.
    059        Element element = writer.element("p", "class", "help-block invisible");
    060
    061        resources.renderInformalParameters(writer);
    062
    063        // Wait until the end of the heartbeat to ensure the Field has had a chance to render.
    064        updateElement(element);
    065
    066        writer.end();
    067
    068        return false;
    069    }
    070
    071    @HeartbeatDeferred
    072    private void updateElement(final Element element)
    073    {
    074        // The field may add an id attribute because of this call.
    075        element.attribute("data-error-block-for", field.getClientId());
    076    }
    077}