001// Copyright 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;
016
017/**
018 * Defines a field within a form.  Fields have a <a href="http://www.w3.org/TR/html4/interact/forms.html#control-name">control
019 * name</a> that is used when rendering and, later, when the form is submitted, to identify the query parameter.
020 * <p/>
021 * Timing is important, as components may render multiple times, due to looping and other factors. Generally, a
022 * component's {@link #getControlName()} will only be accurate after it has rendered.  In some cases, when generating
023 * JavaScript for example, it is necessary to {@linkplain org.apache.tapestry5.services.Heartbeat#defer(Runnable) wait
024 * until the end of the current Heartbeat} to ensure that all components have had their chance to render.
025 */
026public interface Field extends ClientElement
027{
028    /**
029     * Returns the value used as the name attribute of the rendered element. This value will be unique within an
030     * enclosing form, even if the same component renders multiple times.
031     *
032     * @see org.apache.tapestry5.services.FormSupport#allocateControlName(String)
033     */
034    String getControlName();
035
036    /**
037     * Returns a user presentable (localized) label for the field, which may be used inside &lt;label&gt; elements on
038     * the client, and inside client or server-side validation error messages.
039     *
040     * @return the label
041     * @see org.apache.tapestry5.corelib.components.Label
042     */
043    String getLabel();
044
045    /**
046     * Returns true if the field is disabled; A disabled field will render a disabled attribute so that it is
047     * non-responsive on the client (at least, until its disabled status is changed on the client using JavaScript). A
048     * disabled field will ignore any value passed up in a form submit request. Care must be taken if the disabled
049     * status of a field can change between the time the field is rendered and the time the enclosing form is
050     * submitted.
051     */
052    boolean isDisabled();
053
054    /**
055     * Returns true if this field required (as per {@link org.apache.tapestry5.FieldValidator#isRequired()}).
056     *
057     * @return true if a non-blank value is required for the field
058     */
059    boolean isRequired();
060}