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.*;
016import org.apache.tapestry5.annotations.Environmental;
017import org.apache.tapestry5.annotations.HeartbeatDeferred;
018import org.apache.tapestry5.annotations.Parameter;
019import org.apache.tapestry5.annotations.SupportsInformalParameters;
020import org.apache.tapestry5.dom.Element;
021import org.apache.tapestry5.ioc.annotations.Inject;
022import org.apache.tapestry5.ioc.annotations.Symbol;
023import org.apache.tapestry5.ioc.internal.util.InternalUtils;
024import org.apache.tapestry5.services.javascript.JavaScriptSupport;
025
026/**
027 * Generates a <label> element for a particular field. It writes the CSS class "control-label".
028 *
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    @Inject
053    private JavaScriptSupport javaScriptSupport;
054
055    @Inject
056    @Symbol(SymbolConstants.PRODUCTION_MODE)
057    private boolean productionMode;
058
059    /**
060     * If true, then the body of the label element (in the template) is ignored. This is used when a designer places a
061     * value inside the <label> element for WYSIWYG purposes, but it should be replaced with a different
062     * (probably, localized) value at runtime. The default is false, so a body will be used if present and the field's
063     * label will only be used if the body is empty or blank.
064     */
065    @Parameter
066    private boolean ignoreBody;
067
068    private Element labelElement;
069
070    boolean beginRender(MarkupWriter writer)
071    {
072        decorator.beforeLabel(field);
073
074        labelElement = writer.element("label", "class", "control-label");
075
076        resources.renderInformalParameters(writer);
077
078        // Since we don't know if the field has rendered yet, we need to defer writing the for and id
079        // attributes until we know the field has rendered (and set its clientId property). That's
080        // exactly what Heartbeat is for.
081
082        updateAttributes();
083
084        return !ignoreBody;
085    }
086
087    @HeartbeatDeferred
088    private void updateAttributes()
089    {
090        String fieldId = field.getClientId();
091
092        if (!productionMode && fieldId == null)
093        {
094            // TAP5-2500
095            String warningText = "The Label component " + resources.getCompleteId()
096              + " is linked to a Field that failed to return a clientId. The 'for' attibute will not be rendered.";
097            javaScriptSupport.require("t5/core/console").invoke("warn").with(warningText);
098        }
099
100        labelElement.forceAttributes("for", fieldId);
101        decorator.insideLabel(field, labelElement);
102    }
103
104    void afterRender(MarkupWriter writer)
105    {
106        // If the Label element has a body that renders some non-blank output, that takes precedence
107        // over the label string provided by the field.
108
109        boolean bodyIsBlank = InternalUtils.isBlank(labelElement.getChildMarkup());
110
111        if (bodyIsBlank)
112            writer.write(field.getLabel());
113
114        writer.end(); // label
115
116        decorator.afterLabel(field);
117    }
118}