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}