    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.BindingConstants;
    016import org.apache.tapestry5.ComponentResources;
    017import org.apache.tapestry5.Field;
    018import org.apache.tapestry5.MarkupWriter;
    019import org.apache.tapestry5.SymbolConstants;
    020import org.apache.tapestry5.annotations.HeartbeatDeferred;
    021import org.apache.tapestry5.annotations.Parameter;
    022import org.apache.tapestry5.annotations.SupportsInformalParameters;
    023import org.apache.tapestry5.dom.Element;
    024import org.apache.tapestry5.ioc.annotations.Inject;
    025import org.apache.tapestry5.ioc.annotations.Symbol;
    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 CSS class]">}, where {@code [form group CSS class]}
    032 * is defined by the value of the {@link SymbolConstants#FORM_GROUP_WRAPPER_CSS_CLASS}
    033 * configuration symbol ({@code tapestry.form-group-wrapper-css-class}).
    034 *
    035 * It is acceptable to include multiple Errors components for a single field; this is sometimes necessary
    036 * when creating a responsive layout - which should probably ensure that only one of the Errors is
    037 * visible at any time.
    038 *
    039 * Errors is optional, and Tapestry's client-side logic will do a reasonable job of placing a help block
    040 * dynamically when a validation error must be presented; this component is intended for use when the default logic
    041 * doesn't place the help block in the right spot.
    042 *
    043 * @tapestrydoc
    044 * @since 5.2.0
    045 */
    046@SupportsInformalParameters
    047public class Error
    048{
    049    /**
    050     * The for parameter is used to identify the {@link Field} to present errors of.
    051     */
    052    @Parameter(name = "for", required = true, allowNull = false, defaultPrefix = BindingConstants.COMPONENT)
    053    private Field field;
    054
    055    @Inject
    056    private ComponentResources resources;
    057
    058    @Inject
    059    @Symbol(SymbolConstants.ERROR_CSS_CLASS)
    060    private String cssClass;
    061
    062    boolean beginRender(final MarkupWriter writer)
    063    {
    064        // Initially invisible; will be shown on client if an error exists.
    065        Element element = writer.element("p", "class",
    066                !("help-block".equals(cssClass)) ? ("help-block " + cssClass) : cssClass + " invisible",
    067                        "role", "alert");
    068
    069        resources.renderInformalParameters(writer);
    070
    071        // Wait until the end of the heartbeat to ensure the Field has had a chance to render.
    072        updateElement(element);
    073
    074        writer.end();
    075
    076        return false;
    077    }
    078
    079    @HeartbeatDeferred
    080    private void updateElement(final Element element)
    081    {
    082        // The field may add an id attribute because of this call.
    083        element.attribute("data-error-block-for", field.getClientId());
    084        String id = field.getClientId() + "-help-block";
    085        element.attribute("id", id);
    086        Element input = element.getDocument().getElementById(field.getClientId());
    087        if (input != null) {
    088            input.attribute("aria-describedby", id);
    089        }
    090    }
    091}