Java tutorial
/* * Copyright 2010 Google Inc. * * 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.google.gwt.cell.client; import com.google.gwt.core.client.GWT; import com.google.gwt.dom.client.Element; import com.google.gwt.dom.client.EventTarget; import com.google.gwt.dom.client.NativeEvent; import com.google.gwt.dom.client.Style.Display; import com.google.gwt.resources.client.ClientBundle; import com.google.gwt.resources.client.ImageResource; import com.google.gwt.safehtml.client.SafeHtmlTemplates; import com.google.gwt.safehtml.shared.SafeHtml; import com.google.gwt.safehtml.shared.SafeHtmlBuilder; import com.google.gwt.safehtml.shared.SafeHtmlUtils; import com.google.gwt.text.shared.AbstractSafeHtmlRenderer; import com.google.gwt.text.shared.SafeHtmlRenderer; import com.google.gwt.user.client.ui.AbstractImagePrototype; /** * An {@link AbstractCell} used to render an image. A loading indicator is used * until the image is fully loaded. The String value is the url of the image. */ public class ImageLoadingCell extends AbstractCell<String> { /** * The renderers used by this cell. */ public interface Renderers { /** * Get the renderer used to render an error message when the image does not * load. By default, the broken image is rendered. * * @return the {@link SafeHtmlRenderer} used when the image doesn't load */ SafeHtmlRenderer<String> getErrorRenderer(); /** * Get the renderer used to render the image. This renderer must render an * <code>img</code> element, which triggers the <code>load</code> or <code> * error</code> event that this cell handles. * * @return the {@link SafeHtmlRenderer} used to render the image */ SafeHtmlRenderer<String> getImageRenderer(); /** * Get the renderer used to render a loading message. By default, an * animated loading icon is rendered. * * @return the {@link SafeHtmlRenderer} used to render the loading html */ SafeHtmlRenderer<String> getLoadingRenderer(); } interface Template extends SafeHtmlTemplates { @Template("<div style='height:0px;width:0px;overflow:hidden;'>{0}</div>") SafeHtml image(SafeHtml imageHtml); @Template("<img src=\"{0}\"/>") SafeHtml img(String url); @Template("<div>{0}</div>") SafeHtml loading(SafeHtml loadingHtml); } private static Template template; /** * The default {@link SafeHtmlRenderer SafeHtmlRenderers}. */ public static class DefaultRenderers implements Renderers { private static SafeHtmlRenderer<String> IMAGE_RENDERER; private static SafeHtmlRenderer<String> LOADING_RENDERER; public DefaultRenderers() { if (IMAGE_RENDERER == null) { IMAGE_RENDERER = new AbstractSafeHtmlRenderer<String>() { public SafeHtml render(String object) { return template.img(object); } }; } if (LOADING_RENDERER == null) { Resources resources = GWT.create(Resources.class); ImageResource res = resources.loading(); final String loadingHtml = AbstractImagePrototype.create(res).getHTML(); LOADING_RENDERER = new AbstractSafeHtmlRenderer<String>() { public SafeHtml render(String object) { return SafeHtmlUtils.fromSafeConstant(loadingHtml); } }; } } /** * Returns the renderer for a broken image. * * @return a {@link SafeHtmlRenderer SafeHtmlRenderer<String>} instance */ public SafeHtmlRenderer<String> getErrorRenderer() { // Show the broken image on error. return getImageRenderer(); } /** * Returns the renderer for an image. * * @return a {@link SafeHtmlRenderer SafeHtmlRenderer<String>} instance */ public SafeHtmlRenderer<String> getImageRenderer() { return IMAGE_RENDERER; } /** * Returns the renderer for a loading image. * * @return a {@link SafeHtmlRenderer SafeHtmlRenderer<String>} instance */ public SafeHtmlRenderer<String> getLoadingRenderer() { return LOADING_RENDERER; } } /** * The images used by the {@link DefaultRenderers}. */ interface Resources extends ClientBundle { ImageResource loading(); } private final SafeHtmlRenderer<String> errorRenderer; private final SafeHtmlRenderer<String> imageRenderer; private final SafeHtmlRenderer<String> loadingRenderer; /** * <p> * Construct an {@link ImageResourceCell} using the {@link DefaultRenderers}. * </p> * <p> * The {@link DefaultRenderers} will be constructed using * {@link GWT#create(Class)}, which allows you to replace the class using a * deferred binding. * </p> */ public ImageLoadingCell() { this(GWT.<DefaultRenderers>create(DefaultRenderers.class)); } /** * Construct an {@link ImageResourceCell} using the specified * {@link SafeHtmlRenderer SafeHtmlRenderers}. * * @param renderers an instance of {@link ImageLoadingCell.Renderers Renderers} */ public ImageLoadingCell(Renderers renderers) { super("load", "error"); if (template == null) { template = GWT.create(Template.class); } this.errorRenderer = renderers.getErrorRenderer(); this.imageRenderer = renderers.getImageRenderer(); this.loadingRenderer = renderers.getLoadingRenderer(); } @Override public void onBrowserEvent(Context context, Element parent, String value, NativeEvent event, ValueUpdater<String> valueUpdater) { // The loading indicator can fire its own load or error event, so we check // that the event actually occurred on the main image. String type = event.getType(); if ("load".equals(type) && eventOccurredOnImage(event, parent)) { // Remove the loading indicator. parent.getFirstChildElement().getStyle().setDisplay(Display.NONE); // Show the image. Element imgWrapper = parent.getChild(1).cast(); imgWrapper.getStyle().setProperty("height", "auto"); imgWrapper.getStyle().setProperty("width", "auto"); imgWrapper.getStyle().setProperty("overflow", "auto"); } else if ("error".equals(type) && eventOccurredOnImage(event, parent)) { // Replace the loading indicator with an error message. parent.getFirstChildElement().setInnerHTML(errorRenderer.render(value).asString()); } } @Override public void render(Context context, String value, SafeHtmlBuilder sb) { // We can't use ViewData because we don't know the caching policy of the // browser. The browser may fetch the image every time we render. if (value != null) { sb.append(template.loading(loadingRenderer.render(value))); sb.append(template.image(imageRenderer.render(value))); } } /** * Check whether or not an event occurred within the wrapper around the image * element. * * @param event the event * @param parent the parent element * @return true if the event targets the image */ private boolean eventOccurredOnImage(NativeEvent event, Element parent) { EventTarget eventTarget = event.getEventTarget(); if (!Element.is(eventTarget)) { return false; } Element target = eventTarget.cast(); // Make sure the target occurred within the div around the image. Element imgWrapper = parent.getFirstChildElement().getNextSiblingElement(); return imgWrapper.isOrHasChild(target); } }