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