Java tutorial
/* * Copyright 2000-2018 Vaadin Ltd. * * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy of * the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations under * the License. */ package com.vaadin.client.ui.aria; import com.google.gwt.aria.client.Id; import com.google.gwt.aria.client.InvalidValue; import com.google.gwt.aria.client.Roles; import com.google.gwt.dom.client.Element; import com.google.gwt.user.client.DOM; import com.google.gwt.user.client.ui.Widget; /** * Helper class that helps to implement the WAI-ARIA functionality. */ public class AriaHelper { public static final String ASSISTIVE_DEVICE_ONLY_STYLE = "v-assistive-device-only"; /** * Binds a caption (label in HTML speak) to the form element as required by * WAI-ARIA specification. * * @param widget * Widget, that should be bound to the caption * @param captionElement * Element with of caption to bind */ public static void bindCaption(Widget widget, Element captionElement) { assert widget != null : "Valid Widget required"; if (widget instanceof HandlesAriaCaption) { // Let the widget handle special cases itself if (captionElement == null) { ((HandlesAriaCaption) widget).bindAriaCaption(null); } else { ensureHasId(captionElement); ((HandlesAriaCaption) widget).bindAriaCaption(DOM.asOld(captionElement)); } } else if (captionElement != null) { // Handle the default case ensureHasId(captionElement); String ownerId = ensureHasId(widget.getElement()); captionElement.setAttribute("for", ownerId); Roles.getTextboxRole().setAriaLabelledbyProperty(widget.getElement(), Id.of(captionElement)); } else { clearCaption(widget); } } /** * Removes a binding to a caption added with bindCaption() from the provided * Widget. * * @param widget * Widget, that was bound to a caption before */ private static void clearCaption(Widget widget) { Roles.getTextboxRole().removeAriaLabelledbyProperty(widget.getElement()); } /** * Handles the required actions depending of the input Widget being required * or not. * * @param widget * Widget, typically an input Widget like TextField * @param required * boolean, true when the element is required */ public static void handleInputRequired(Widget widget, boolean required) { assert widget != null : "Valid Widget required"; if (widget instanceof HandlesAriaRequired) { ((HandlesAriaRequired) widget).setAriaRequired(required); } else { handleInputRequired(widget.getElement(), required); } } /** * Handles the required actions depending of the input element being * required or not. * * @param element * Element, typically from an input Widget like TextField * @param required * boolean, true when the element is required */ public static void handleInputRequired(Element element, boolean required) { if (required) { Roles.getTextboxRole().setAriaRequiredProperty(element, required); } else { Roles.getTextboxRole().removeAriaRequiredProperty(element); } } /** * Handles the required actions depending of the input Widget contains * unaccepted input. * * @param widget * Widget, typically an input Widget like TextField * @param invalid * boolean, true when the Widget input has an error */ public static void handleInputInvalid(Widget widget, boolean invalid) { assert widget != null : "Valid Widget required"; if (widget instanceof HandlesAriaInvalid) { ((HandlesAriaInvalid) widget).setAriaInvalid(invalid); } else { handleInputInvalid(widget.getElement(), invalid); } } /** * Handles the required actions depending of the input element contains * unaccepted input. * * @param element * Element, typically an input Widget like TextField * @param invalid * boolean, true when the element input has an error */ public static void handleInputInvalid(Element element, boolean invalid) { if (invalid) { Roles.getTextboxRole().setAriaInvalidState(element, InvalidValue.TRUE); } else { Roles.getTextboxRole().removeAriaInvalidState(element); } } /** * Makes sure that the provided element has an id attribute. Adds a new * unique id if not. * * @param element * Element to check * @return String with the id of the element */ public static String ensureHasId(Element element) { assert element != null : "Valid Element required"; String id = element.getId(); if (null == id || id.isEmpty()) { id = DOM.createUniqueId(); element.setId(id); } return id; } /** * Allows to move an element out of the visible area of the browser window. * * This makes it possible to have additional information for an assistive * device, that is not in the way for visual users. * * @param element * Element to move out of sight * @param assistiveOnly * {@code true} when element should only be visible for assistive * devices, {@code false} to make the element visible for all */ public static void setVisibleForAssistiveDevicesOnly(Element element, boolean assistiveOnly) { if (assistiveOnly) { element.addClassName(ASSISTIVE_DEVICE_ONLY_STYLE); } else { element.removeClassName(ASSISTIVE_DEVICE_ONLY_STYLE); } } }