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/*
 * 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 {

  /**
   * 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 getErrorRenderer();

    /**
     * Get the renderer used to render the image. This renderer must render an
     * img element, which triggers the load or 
     * error event that this cell handles.
     *
     * @return the {@link SafeHtmlRenderer} used to render the image
     */
    SafeHtmlRenderer 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 getLoadingRenderer();
  }

  interface Template extends SafeHtmlTemplates {
    @Template("
{0}
") SafeHtml image(SafeHtml imageHtml); @Template("") SafeHtml img(String url); @Template("
{0}
") SafeHtml loading(SafeHtml loadingHtml); } private static Template template; /** * The default {@link SafeHtmlRenderer SafeHtmlRenderers}. */ public static class DefaultRenderers implements Renderers { private static SafeHtmlRenderer IMAGE_RENDERER; private static SafeHtmlRenderer LOADING_RENDERER; public DefaultRenderers() { if (IMAGE_RENDERER == null) { IMAGE_RENDERER = new AbstractSafeHtmlRenderer() { 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() { public SafeHtml render(String object) { return SafeHtmlUtils.fromSafeConstant(loadingHtml); } }; } } /** * Returns the renderer for a broken image. * * @return a {@link SafeHtmlRenderer SafeHtmlRenderer} instance */ public SafeHtmlRenderer getErrorRenderer() { // Show the broken image on error. return getImageRenderer(); } /** * Returns the renderer for an image. * * @return a {@link SafeHtmlRenderer SafeHtmlRenderer} instance */ public SafeHtmlRenderer getImageRenderer() { return IMAGE_RENDERER; } /** * Returns the renderer for a loading image. * * @return a {@link SafeHtmlRenderer SafeHtmlRenderer} instance */ public SafeHtmlRenderer getLoadingRenderer() { return LOADING_RENDERER; } } /** * The images used by the {@link DefaultRenderers}. */ interface Resources extends ClientBundle { ImageResource loading(); } private final SafeHtmlRenderer errorRenderer; private final SafeHtmlRenderer imageRenderer; private final SafeHtmlRenderer loadingRenderer; /** *

* Construct an {@link ImageResourceCell} using the {@link DefaultRenderers}. *

*

* The {@link DefaultRenderers} will be constructed using * {@link GWT#create(Class)}, which allows you to replace the class using a * deferred binding. *

*/ public ImageLoadingCell() { this(GWT. 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 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); } }




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