    001// Copyright 2006-2013 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.*;
    018import org.apache.tapestry5.annotations.Environmental;
    019import org.apache.tapestry5.annotations.HeartbeatDeferred;
    020import org.apache.tapestry5.annotations.Parameter;
    021import org.apache.tapestry5.annotations.SupportsInformalParameters;
    022import org.apache.tapestry5.dom.Element;
    023import org.apache.tapestry5.ioc.annotations.Inject;
    024import org.apache.tapestry5.ioc.internal.util.InternalUtils;
    025
    026/**
    027 * Generates a &lt;label&gt; element for a particular field. It writes the CSS class "control-label".
    028 * <p/>
    029 * A Label will render its body, if it has one. However, in most cases it will not have a body, and will render its
    030 * {@linkplain org.apache.tapestry5.Field#getLabel() field's label} as its body. Remember, however, that it is the
    031 * field label that will be used in any error messages. The Label component allows for client- and server-side
    032 * validation error decorations.
    033 *
    034 * @tapestrydoc
    035 */
    036@SupportsInformalParameters
    037public class Label
    038{
    039    /**
    040     * The for parameter is used to identify the {@link Field} linked to this label (it is named this way because it
    041     * results in the for attribute of the label element).
    042     */
    043    @Parameter(name = "for", required = true, allowNull = false, defaultPrefix = BindingConstants.COMPONENT)
    044    private Field field;
    045
    046    @Environmental
    047    private ValidationDecorator decorator;
    048
    049    @Inject
    050    private ComponentResources resources;
    051
    052    /**
    053     * If true, then the body of the label element (in the template) is ignored. This is used when a designer places a
    054     * value inside the &lt;label&gt; element for WYSIWYG purposes, but it should be replaced with a different
    055     * (probably, localized) value at runtime. The default is false, so a body will be used if present and the field's
    056     * label will only be used if the body is empty or blank.
    057     */
    058    @Parameter
    059    private boolean ignoreBody;
    060
    061    private Element labelElement;
    062
    063    boolean beginRender(MarkupWriter writer)
    064    {
    065        decorator.beforeLabel(field);
    066
    067        labelElement = writer.element("label", "class", "control-label");
    068
    069        resources.renderInformalParameters(writer);
    070
    071        // Since we don't know if the field has rendered yet, we need to defer writing the for and id
    072        // attributes until we know the field has rendered (and set its clientId property). That's
    073        // exactly what Heartbeat is for.
    074
    075        updateAttributes();
    076
    077        return !ignoreBody;
    078    }
    079
    080    @HeartbeatDeferred
    081    private void updateAttributes()
    082    {
    083        String fieldId = field.getClientId();
    084
    085        labelElement.forceAttributes("for", fieldId);
    086
    087        decorator.insideLabel(field, labelElement);
    088    }
    089
    090    void afterRender(MarkupWriter writer)
    091    {
    092        // If the Label element has a body that renders some non-blank output, that takes precedence
    093        // over the label string provided by the field.
    094
    095        boolean bodyIsBlank = InternalUtils.isBlank(labelElement.getChildMarkup());
    096
    097        if (bodyIsBlank)
    098            writer.write(field.getLabel());
    099
    100        writer.end(); // label
    101
    102        decorator.afterLabel(field);
    103    }
    104}