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}