    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 * <p/>
    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 * <p/>
    024 * Most Fields also implement {@link org.apache.tapestry5.Field2}, which was introduced to bridge a gap related to
    025 * re-rendering a form as part of an Ajax request.
    026 */
    027public interface Field extends ClientElement
    028{
    029    /**
    030     * Returns the value used as the name attribute of the rendered element. This value will be unique within an
    031     * enclosing form, even if the same component renders multiple times.
    032     *
    033     * @see org.apache.tapestry5.services.FormSupport#allocateControlName(String)
    034     */
    035    String getControlName();
    036
    037    /**
    038     * Returns a user presentable (localized) label for the field, which may be used inside &lt;label&gt; elements on
    039     * the client, and inside client or server-side validation error messages.
    040     *
    041     * @return the label
    042     * @see org.apache.tapestry5.corelib.components.Label
    043     */
    044    String getLabel();
    045
    046    /**
    047     * Returns true if the field is disabled; A disabled field will render a disabled attribute so that it is
    048     * non-responsive on the client (at least, until its disabled status is changed on the client using JavaScript). A
    049     * disabled field will ignore any value passed up in a form submit request. Care must be taken if the disabled
    050     * status of a field can change between the time the field is rendered and the time the enclosing form is
    051     * submitted.
    052     */
    053    boolean isDisabled();
    054
    055    /**
    056     * Returns true if this field required (as per {@link org.apache.tapestry5.FieldValidator#isRequired()}).
    057     *
    058     * @return true if a non-blank value is required for the field
    059     */
    060    boolean isRequired();
    061}