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;
014
015/**
016 * Defines a field within a form.  Fields have a <a href="http://www.w3.org/TR/html4/interact/forms.html#control-name">control
017 * name</a> that is used when rendering and, later, when the form is submitted, to identify the query parameter.
018 *
019 * Timing is important, as components may render multiple times, due to looping and other factors. Generally, a
020 * component's {@link #getControlName()} will only be accurate after it has rendered.  In some cases, when generating
021 * JavaScript for example, it is necessary to {@linkplain org.apache.tapestry5.services.Heartbeat#defer(Runnable) wait
022 * until the end of the current Heartbeat} to ensure that all components have had their chance to render.
023 */
024public interface Field extends ClientElement
025{
026    /**
027     * @return the value used as the name attribute of the rendered element. This value will be unique within an
028     * enclosing form, even if the same component renders multiple times.
029     *
030     * @see org.apache.tapestry5.services.FormSupport#allocateControlName(String)
031     */
032    String getControlName();
033
034    /**
035     * Returns a user presentable (localized) label for the field, which may be used inside &lt;label&gt; elements on
036     * the client, and inside client or server-side validation error messages.
037     *
038     * @return the label
039     * @see org.apache.tapestry5.corelib.components.Label
040     */
041    String getLabel();
042
043    /**
044     * Returns true if the field is disabled; A disabled field will render a disabled attribute so that it is
045     * non-responsive on the client (at least, until its disabled status is changed on the client using JavaScript). A
046     * disabled field will ignore any value passed up in a form submit request. Care must be taken if the disabled
047     * status of a field can change between the time the field is rendered and the time the enclosing form is
048     * submitted.
049     * @return true if disabled, false otherwise
050     */
051    boolean isDisabled();
052
053    /**
054     * Returns true if this field required (as per {@link org.apache.tapestry5.FieldValidator#isRequired()}).
055     *
056     * @return true if a non-blank value is required for the field
057     */
058    boolean isRequired();
059}