user/src/com/google/gwt/cell/client/ButtonCellBase.java - gwt - Git at Google

 /*
  * Copyright 2011 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 static com.google.gwt.dom.client.BrowserEvents.CLICK;
 import static com.google.gwt.dom.client.BrowserEvents.KEYDOWN;
 import static com.google.gwt.dom.client.BrowserEvents.MOUSEDOWN;

 import com.google.gwt.core.client.GWT;
 import com.google.gwt.dom.client.BrowserEvents;
 import com.google.gwt.dom.client.Element;
 import com.google.gwt.dom.client.NativeEvent;
 import com.google.gwt.dom.client.Style.Unit;
 import com.google.gwt.event.shared.HandlerRegistration;
 import com.google.gwt.i18n.client.LocaleInfo;
 import com.google.gwt.resources.client.ClientBundle;
 import com.google.gwt.resources.client.CommonResources;
 import com.google.gwt.resources.client.CssResource;
 import com.google.gwt.resources.client.CssResource.ImportedWithPrefix;
 import com.google.gwt.resources.client.ImageResource;
 import com.google.gwt.resources.client.ImageResource.ImageOptions;
 import com.google.gwt.resources.client.ImageResource.RepeatStyle;
 import com.google.gwt.safecss.shared.SafeStyles;
 import com.google.gwt.safecss.shared.SafeStylesBuilder;
 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.SafeHtmlRenderer;
 import com.google.gwt.user.client.Event;
 import com.google.gwt.user.client.Event.NativePreviewEvent;
 import com.google.gwt.user.client.Event.NativePreviewHandler;
 import com.google.gwt.user.client.ui.AbstractImagePrototype;
 import com.google.gwt.user.client.ui.HasEnabled;

 /**
  * Base class for button Cells.
  *
  * @param <C> the type that this Cell represents
  */
 public class ButtonCellBase<C> extends AbstractCell<C> implements IsCollapsible, HasEnabled {

   /**
    * The appearance used to render this Cell.
    *
    * @param <C> the type that this Cell represents
    */
   public interface Appearance<C> {

     /**
      * Called when the user pushes the button down.
      *
      * @param parent the parent Element
      */
     void onPush(Element parent);

     /**
      * Called when the user releases the button from being pushed.
      *
      * @param parent the parent Element
      */
     void onUnpush(Element parent);

     /**
      * Render the button and its contents.
      *
      * @param cell the cell that is being rendered
      * @param context the {@link Context} of the cell
      * @param value the value that generated the content
      * @param sb the {@link SafeHtmlBuilder} to render into
      */
     void render(ButtonCellBase<C> cell, Context context, C value, SafeHtmlBuilder sb);

     /**
      * Explicitly focus/unfocus this cell.
      *
      * @param parent the parent element
      * @param focused whether this cell should take focus or release it
      */
     void setFocus(Element parent, boolean focused);
   }

   /**
    * The decoration applied to the button.
    *
    * <dl>
    * <dt>DEFAULT</dt>
    * <dd>A general button used in any context.</dd>
    * <dt>PRIMARY</dt>
    * <dd>A primary button that stands out against other buttons.</dd>
    * <dt>NEGATIVE</dt>
    * <dd>A button that results in a negative action, such as delete or cancel</dd>
    * </dl>
    */
   public static enum Decoration {
     DEFAULT, PRIMARY, NEGATIVE;
   }

   /**
    * The default implementation of the {@link ButtonCellBase.Appearance}.
    *
    * @param <C> the type that this Cell represents
    */
   public static class DefaultAppearance<C> implements Appearance<C> {

     /**
      * The resources used by this appearance.
      */
     public interface Resources extends ClientBundle {

       /**
        * The background image applied to the button.
        */
       @ImageOptions(repeatStyle = RepeatStyle.Horizontal, flipRtl = true)
       ImageResource buttonCellBaseBackground();

       @Source(Style.DEFAULT_CSS)
       Style buttonCellBaseStyle();
     }

     /**
      * The Styles used by this appearance.
      */
     @ImportedWithPrefix("gwt-ButtonCellBase")
     public interface Style extends CssResource {
       String DEFAULT_CSS = "com/google/gwt/cell/client/ButtonCellBase.css";

       /**
        * Applied to the button.
        */
       String buttonCellBase();

       /**
        * Applied to the button when it has a collapsed left side.
        */
       String buttonCellBaseCollapseLeft();

       /**
        * Applied to the button when it has a collapsed right side.
        */
       String buttonCellBaseCollapseRight();

       /**
        * Applied to default buttons.
        */
       String buttonCellBaseDefault();

       /**
        * Applied to negative buttons.
        */
       String buttonCellBaseNegative();

       /**
        * Applied to primary buttons.
        */
       String buttonCellBasePrimary();

       /**
        * Applied to the button when being pushed.
        */
       String buttonCellBasePushing();
     }

     /**
      * The templates used by this appearance.
      */
     interface Template extends SafeHtmlTemplates {
       /**
        * Positions the icon next to the text.
        *
        * NOTE: zoom:0 is a workaround for an IE7 bug where the button contents
        * wrap even when they do not need to.
        */
       @SafeHtmlTemplates.Template("<div class=\"{0}\""
           + " style=\"{1}position:relative;zoom:0;\">{2}{3}</div>")
       SafeHtml iconContentLayout(
           String classes, SafeStyles styles, SafeHtml icon, SafeHtml cellContents);

       /**
        * The wrapper around the icon that aligns it vertically with the text.
        */
       @SafeHtmlTemplates.Template("<div style=\"{0}position:absolute;top:50%;line-height:0px;\">"
           + "{1}</div>")
       SafeHtml iconWrapper(SafeStyles styles, SafeHtml image);
     }

     private static final int DEFAULT_ICON_PADDING = 3;
     private static Resources defaultResources;
     private static Template template;

     private static Resources getDefaultResources() {
       if (defaultResources == null) {
         defaultResources = GWT.create(Resources.class);
       }
       return defaultResources;
     }

     private SafeHtml iconSafeHtml = SafeHtmlUtils.EMPTY_SAFE_HTML;
     private ImageResource lastIcon;
     private final SafeHtmlRenderer<C> renderer;
     private final Style style;

     /**
      * Construct a new {@link ButtonCellBase.DefaultAppearance} using the default styles.
      *
      * @param renderer the {@link SafeHtmlRenderer} used to render the contents
      */
     public DefaultAppearance(SafeHtmlRenderer<C> renderer) {
       this(renderer, getDefaultResources());
     }

     /**
      * Construct a new {@link ButtonCellBase.DefaultAppearance} using the specified resources.
      *
      * @param renderer the {@link SafeHtmlRenderer} used to render the contents
      * @param resources the resources and styles to apply to the button
      */
     public DefaultAppearance(SafeHtmlRenderer<C> renderer, Resources resources) {
       this.renderer = renderer;
       this.style = resources.buttonCellBaseStyle();
       this.style.ensureInjected();
       if (template == null) {
         template = GWT.create(Template.class);
       }
     }

     /**
      * Return the {@link SafeHtmlRenderer} used by this Appearance to render the
      * contents of the button.
      *
      * @return a {@link SafeHtmlRenderer} instance
      */
     public SafeHtmlRenderer<C> getRenderer() {
       return renderer;
     }

     @Override
     public void onPush(Element parent) {
       parent.getFirstChildElement().addClassName(style.buttonCellBasePushing());
     }

     @Override
     public void onUnpush(Element parent) {
       parent.getFirstChildElement().removeClassName(style.buttonCellBasePushing());
     }

     @Override
     public void render(ButtonCellBase<C> cell, Context context, C value, SafeHtmlBuilder sb) {
       // Determine the classes from the state of the button.
       SafeHtmlBuilder classes = new SafeHtmlBuilder();
       classes.appendEscaped(style.buttonCellBase());
       Decoration decoration = cell.getDecoration();
       if (decoration == Decoration.PRIMARY) {
         classes.appendEscaped(" " + style.buttonCellBasePrimary());
       } else if (decoration == Decoration.NEGATIVE) {
         classes.appendEscaped(" " + style.buttonCellBaseNegative());
       } else {
         classes.appendEscaped(" " + style.buttonCellBaseDefault());
       }
       if (cell.isCollapseLeft()) {
         classes.appendEscaped(" " + style.buttonCellBaseCollapseLeft());
       }
       if (cell.isCollapseRight()) {
         classes.appendEscaped(" " + style.buttonCellBaseCollapseRight());
       }

       // Update the cached HTML string used for the icon if the icon changes.
       ImageResource icon = cell.getIcon();
       if (icon != lastIcon) {
         if (icon == null) {
           iconSafeHtml = SafeHtmlUtils.EMPTY_SAFE_HTML;
         } else {
           AbstractImagePrototype proto = AbstractImagePrototype.create(icon);
           SafeHtml iconOnly = proto.getSafeHtml();
           int halfHeight = (int) Math.round(icon.getHeight() / 2.0);
           SafeStylesBuilder styles = new SafeStylesBuilder();
           styles.marginTop(-halfHeight, Unit.PX);
           if (LocaleInfo.getCurrentLocale().isRTL()) {
             styles.right(0, Unit.PX);
           } else {
             styles.left(0, Unit.PX);
           }
           iconSafeHtml = template.iconWrapper(styles.toSafeStyles(), iconOnly);
         }
       }

       // Figure out the attributes.
       char accessKey = cell.getAccessKey();
       StringBuilder attributes = new StringBuilder();
       if (!cell.isEnabled()) {
         attributes.append("disabled=disabled ");
       }
       if (accessKey != 0) {
         attributes.append("accessKey=\"").append(SafeHtmlUtils.htmlEscape("" + accessKey));
         attributes.append("\" ");
       }

       // Create the button.
       SafeStylesBuilder styles = new SafeStylesBuilder();
       int iconWidth = (icon == null) ? 0 : icon.getWidth();
       int iconPadding = iconWidth + DEFAULT_ICON_PADDING;
       if (LocaleInfo.getCurrentLocale().isRTL()) {
         styles.paddingRight(iconPadding, Unit.PX);
       } else {
         styles.paddingLeft(iconPadding, Unit.PX);
       }
       SafeHtml safeValue = renderer.render(value);
       SafeHtml content = template.iconContentLayout(
           CommonResources.getInlineBlockStyle(), styles.toSafeStyles(), iconSafeHtml, safeValue);
       int tabIndex = cell.getTabIndex();
       StringBuilder openTag = new StringBuilder();
       openTag.append("<button type=\"button\"");
       openTag.append(" class=\"" + classes.toSafeHtml().asString() + "\"");
       openTag.append(" tabindex=\"" + tabIndex + "\" ");
       openTag.append(attributes.toString()).append(">");
       sb.append(SafeHtmlUtils.fromTrustedString(openTag.toString()));
       sb.append(content);
       sb.appendHtmlConstant("</button>");
     }

     @Override
     public void setFocus(Element parent, boolean focused) {
       Element focusable = parent.getFirstChildElement().cast();
       if (focused) {
         focusable.focus();
       } else {
         focusable.blur();
       }
     }
   }

   /**
    * The {@link NativePreviewHandler} used to unpush a button onmouseup, even if
    * the event doesn't occur over the button.
    */
   private class UnpushHandler implements NativePreviewHandler {

     private final Element parent;
     private final HandlerRegistration reg;

     public UnpushHandler(Element parent) {
       this.parent = parent;
       this.reg = Event.addNativePreviewHandler(this);
     }

     @Override
     public void onPreviewNativeEvent(NativePreviewEvent event) {
       if (BrowserEvents.MOUSEUP.equals(event.getNativeEvent().getType())) {
         // Unregister self.
         reg.removeHandler();

         // Unpush the element.
         appearance.onUnpush(parent);
       }
     }
   }

   private char accessKey;
   private final Appearance<C> appearance;
   private Decoration decoration = Decoration.DEFAULT;
   private ImageResource icon;
   private boolean isCollapsedLeft;
   private boolean isCollapsedRight;
   private boolean isEnabled = true;

   /**
    * The tab index applied to the buttons. If the button is used in a list of
    * table, a tab index of -1 should be used so it doesn't interrupt the tab
    * sequence.
    */
   private int tabIndex = -1;

   /**
    * Construct a new {@link ButtonCellBase} using the specified
    * {@link Appearance} to render the contents.
    *
    * @param appearance the appearance of the cell
    */
   public ButtonCellBase(Appearance<C> appearance) {
     super(CLICK, KEYDOWN, MOUSEDOWN);
     this.appearance = appearance;
   }

   /**
    * Get the access key.
    *
    * @return the access key, or 0 if one is not defined
    */
   public char getAccessKey() {
     return accessKey;
   }

   /**
    * Get the decoration style of the button.
    */
   public Decoration getDecoration() {
     return decoration;
   }

   /**
    * Get the icon displayed next to the button text.
    *
    * @return the icon resource
    */
   public ImageResource getIcon() {
     return icon;
   }

   /**
    * Return the tab index that is given to all rendered cells.
    *
    * @return the tab index
    */
   public int getTabIndex() {
     return tabIndex;
   }

   @Override
   public boolean isCollapseLeft() {
     return this.isCollapsedLeft;
   }

   @Override
   public boolean isCollapseRight() {
     return this.isCollapsedRight;
   }

   @Override
   public boolean isEnabled() {
     return isEnabled;
   }

   @Override
   public void onBrowserEvent(Context context, Element parent, C value, NativeEvent event,
       ValueUpdater<C> valueUpdater) {
     // Ignore all events if disabled.
     if (!isEnabled()) {
       return;
     }

     // Let AbstractCell handle the enter key.
     super.onBrowserEvent(context, parent, value, event, valueUpdater);

     // Ignore events that occur outside of the button element.
     Element target = event.getEventTarget().cast();
     if (!parent.getFirstChildElement().isOrHasChild(target)) {
       return;
     }

     String eventType = event.getType();
     if (CLICK.equals(eventType)) {
       // Click the button.
       onEnterKeyDown(context, parent, value, event, valueUpdater);
     } else if (MOUSEDOWN.equals(eventType)) {
       // Push.
       appearance.onPush(parent);

       /*
        * Add a preview handler to unpush the button onmouseup or onblur, even if
        * the event doesn't occur over the button.
        */
       new UnpushHandler(parent);

       // We will be handling all user visual feedback manually. Prevent browser
       // doing default handling (i.e. double-click highlights button text).
       event.preventDefault();
     }
   }

   @Override
   public void render(Context context, C value, SafeHtmlBuilder sb) {
     appearance.render(this, context, value, sb);
   }

   /**
    * Sets the cell's 'access key'. This key is used (in conjunction with a
    * browser-specific modifier key) to automatically focus the cell.
    *
    * <p>
    * The change takes effect the next time the Cell is rendered.
    *
    * @param key the cell's access key
    */
   public void setAccessKey(char key) {
     this.accessKey = key;
   }

   /**
    * {@inheritDoc}
    *
    * <p>
    * The change takes effect the next time the Cell is rendered.
    */
   @Override
   public void setCollapseLeft(boolean isCollapsed) {
     this.isCollapsedLeft = isCollapsed;
   }

   /**
    * {@inheritDoc}
    *
    * <p>
    * The change takes effect the next time the Cell is rendered.
    */
   @Override
   public void setCollapseRight(boolean isCollapsed) {
     this.isCollapsedRight = isCollapsed;
   }

   /**
    * Set the {@link Decoration} of the button.
    *
    * <p>
    * This change takes effect the next time the cell is rendered.
    *
    * @param decoration the button decoration
    */
   public void setDecoration(Decoration decoration) {
     this.decoration = decoration;
   }

   /**
    * {@inheritDoc}
    *
    * <p>
    * The change takes effect the next time the Cell is rendered.
    */
   @Override
   public void setEnabled(boolean isEnabled) {
     this.isEnabled = isEnabled;
   }

   /**
    * Explicitly focus/unfocus this cell. Only one UI component can have focus at
    * a time, and the component that does will receive all keyboard events.
    *
    * @param parent the parent element
    * @param focused whether this cell should take focus or release it
    */
   public void setFocus(Element parent, boolean focused) {
     appearance.setFocus(parent, focused);
   }

   /**
    * Set the icon to display next to the button text.
    *
    * @param icon the icon resource, or null not to show an icon
    */
   public void setIcon(ImageResource icon) {
     this.icon = icon;
   }

   /**
    * Set the tab index to apply to the button. By default, the tab index is set
    * to -1 so that the button does not interrupt the tab chain when in a table
    * or list. The change takes effect the next time the Cell is rendered.
    *
    * @param tabIndex the tab index
    */
   public void setTabIndex(int tabIndex) {
     this.tabIndex = tabIndex;
   }

   @Override
   protected void onEnterKeyDown(Context context, Element parent, C value, NativeEvent event,
       ValueUpdater<C> valueUpdater) {
     if (valueUpdater != null) {
       valueUpdater.update(value);
     }
   }
 }
	/*
	* Copyright 2011 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 static com.google.gwt.dom.client.BrowserEvents.CLICK;
	import static com.google.gwt.dom.client.BrowserEvents.KEYDOWN;
	import static com.google.gwt.dom.client.BrowserEvents.MOUSEDOWN;

	import com.google.gwt.core.client.GWT;
	import com.google.gwt.dom.client.BrowserEvents;
	import com.google.gwt.dom.client.Element;
	import com.google.gwt.dom.client.NativeEvent;
	import com.google.gwt.dom.client.Style.Unit;
	import com.google.gwt.event.shared.HandlerRegistration;
	import com.google.gwt.i18n.client.LocaleInfo;
	import com.google.gwt.resources.client.ClientBundle;
	import com.google.gwt.resources.client.CommonResources;
	import com.google.gwt.resources.client.CssResource;
	import com.google.gwt.resources.client.CssResource.ImportedWithPrefix;
	import com.google.gwt.resources.client.ImageResource;
	import com.google.gwt.resources.client.ImageResource.ImageOptions;
	import com.google.gwt.resources.client.ImageResource.RepeatStyle;
	import com.google.gwt.safecss.shared.SafeStyles;
	import com.google.gwt.safecss.shared.SafeStylesBuilder;
	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.SafeHtmlRenderer;
	import com.google.gwt.user.client.Event;
	import com.google.gwt.user.client.Event.NativePreviewEvent;
	import com.google.gwt.user.client.Event.NativePreviewHandler;
	import com.google.gwt.user.client.ui.AbstractImagePrototype;
	import com.google.gwt.user.client.ui.HasEnabled;

	/**
	* Base class for button Cells.
	*
	* @param <C> the type that this Cell represents
	*/
	public class ButtonCellBase<C> extends AbstractCell<C> implements IsCollapsible, HasEnabled {

	/**
	* The appearance used to render this Cell.
	*
	* @param <C> the type that this Cell represents
	*/
	public interface Appearance<C> {

	/**
	* Called when the user pushes the button down.
	*
	* @param parent the parent Element
	*/
	void onPush(Element parent);

	/**
	* Called when the user releases the button from being pushed.
	*
	* @param parent the parent Element
	*/
	void onUnpush(Element parent);

	/**
	* Render the button and its contents.
	*
	* @param cell the cell that is being rendered
	* @param context the {@link Context} of the cell
	* @param value the value that generated the content
	* @param sb the {@link SafeHtmlBuilder} to render into
	*/
	void render(ButtonCellBase<C> cell, Context context, C value, SafeHtmlBuilder sb);

	/**
	* Explicitly focus/unfocus this cell.
	*
	* @param parent the parent element
	* @param focused whether this cell should take focus or release it
	*/
	void setFocus(Element parent, boolean focused);
	}

	/**
	* The decoration applied to the button.
	*
	* <dl>
	* <dt>DEFAULT</dt>
	* <dd>A general button used in any context.</dd>
	* <dt>PRIMARY</dt>
	* <dd>A primary button that stands out against other buttons.</dd>
	* <dt>NEGATIVE</dt>
	* <dd>A button that results in a negative action, such as delete or cancel</dd>
	* </dl>
	*/
	public static enum Decoration {
	DEFAULT, PRIMARY, NEGATIVE;
	}

	/**
	* The default implementation of the {@link ButtonCellBase.Appearance}.
	*
	* @param <C> the type that this Cell represents
	*/
	public static class DefaultAppearance<C> implements Appearance<C> {

	/**
	* The resources used by this appearance.
	*/
	public interface Resources extends ClientBundle {

	/**
	* The background image applied to the button.
	*/
	@ImageOptions(repeatStyle = RepeatStyle.Horizontal, flipRtl = true)
	ImageResource buttonCellBaseBackground();

	@Source(Style.DEFAULT_CSS)
	Style buttonCellBaseStyle();
	}

	/**
	* The Styles used by this appearance.
	*/
	@ImportedWithPrefix("gwt-ButtonCellBase")
	public interface Style extends CssResource {
	String DEFAULT_CSS = "com/google/gwt/cell/client/ButtonCellBase.css";

	/**
	* Applied to the button.
	*/
	String buttonCellBase();

	/**
	* Applied to the button when it has a collapsed left side.
	*/
	String buttonCellBaseCollapseLeft();

	/**
	* Applied to the button when it has a collapsed right side.
	*/
	String buttonCellBaseCollapseRight();

	/**
	* Applied to default buttons.
	*/
	String buttonCellBaseDefault();

	/**
	* Applied to negative buttons.
	*/
	String buttonCellBaseNegative();

	/**
	* Applied to primary buttons.
	*/
	String buttonCellBasePrimary();

	/**
	* Applied to the button when being pushed.
	*/
	String buttonCellBasePushing();
	}

	/**
	* The templates used by this appearance.
	*/
	interface Template extends SafeHtmlTemplates {
	/**
	* Positions the icon next to the text.
	*
	* NOTE: zoom:0 is a workaround for an IE7 bug where the button contents
	* wrap even when they do not need to.
	*/
	@SafeHtmlTemplates.Template("<div class=\"{0}\""
	+ " style=\"{1}position:relative;zoom:0;\">{2}{3}</div>")
	SafeHtml iconContentLayout(
	String classes, SafeStyles styles, SafeHtml icon, SafeHtml cellContents);

	/**
	* The wrapper around the icon that aligns it vertically with the text.
	*/
	@SafeHtmlTemplates.Template("<div style=\"{0}position:absolute;top:50%;line-height:0px;\">"
	+ "{1}</div>")
	SafeHtml iconWrapper(SafeStyles styles, SafeHtml image);
	}

	private static final int DEFAULT_ICON_PADDING = 3;
	private static Resources defaultResources;
	private static Template template;

	private static Resources getDefaultResources() {
	if (defaultResources == null) {
	defaultResources = GWT.create(Resources.class);
	}
	return defaultResources;
	}

	private SafeHtml iconSafeHtml = SafeHtmlUtils.EMPTY_SAFE_HTML;
	private ImageResource lastIcon;
	private final SafeHtmlRenderer<C> renderer;
	private final Style style;

	/**
	* Construct a new {@link ButtonCellBase.DefaultAppearance} using the default styles.
	*
	* @param renderer the {@link SafeHtmlRenderer} used to render the contents
	*/
	public DefaultAppearance(SafeHtmlRenderer<C> renderer) {
	this(renderer, getDefaultResources());
	}

	/**
	* Construct a new {@link ButtonCellBase.DefaultAppearance} using the specified resources.
	*
	* @param renderer the {@link SafeHtmlRenderer} used to render the contents
	* @param resources the resources and styles to apply to the button
	*/
	public DefaultAppearance(SafeHtmlRenderer<C> renderer, Resources resources) {
	this.renderer = renderer;
	this.style = resources.buttonCellBaseStyle();
	this.style.ensureInjected();
	if (template == null) {
	template = GWT.create(Template.class);
	}
	}

	/**
	* Return the {@link SafeHtmlRenderer} used by this Appearance to render the
	* contents of the button.
	*
	* @return a {@link SafeHtmlRenderer} instance
	*/
	public SafeHtmlRenderer<C> getRenderer() {
	return renderer;
	}

	@Override
	public void onPush(Element parent) {
	parent.getFirstChildElement().addClassName(style.buttonCellBasePushing());
	}

	@Override
	public void onUnpush(Element parent) {
	parent.getFirstChildElement().removeClassName(style.buttonCellBasePushing());
	}

	@Override
	public void render(ButtonCellBase<C> cell, Context context, C value, SafeHtmlBuilder sb) {
	// Determine the classes from the state of the button.
	SafeHtmlBuilder classes = new SafeHtmlBuilder();
	classes.appendEscaped(style.buttonCellBase());
	Decoration decoration = cell.getDecoration();
	if (decoration == Decoration.PRIMARY) {
	classes.appendEscaped(" " + style.buttonCellBasePrimary());
	} else if (decoration == Decoration.NEGATIVE) {
	classes.appendEscaped(" " + style.buttonCellBaseNegative());
	} else {
	classes.appendEscaped(" " + style.buttonCellBaseDefault());
	}
	if (cell.isCollapseLeft()) {
	classes.appendEscaped(" " + style.buttonCellBaseCollapseLeft());
	}
	if (cell.isCollapseRight()) {
	classes.appendEscaped(" " + style.buttonCellBaseCollapseRight());
	}

	// Update the cached HTML string used for the icon if the icon changes.
	ImageResource icon = cell.getIcon();
	if (icon != lastIcon) {
	if (icon == null) {
	iconSafeHtml = SafeHtmlUtils.EMPTY_SAFE_HTML;
	} else {
	AbstractImagePrototype proto = AbstractImagePrototype.create(icon);
	SafeHtml iconOnly = proto.getSafeHtml();
	int halfHeight = (int) Math.round(icon.getHeight() / 2.0);
	SafeStylesBuilder styles = new SafeStylesBuilder();
	styles.marginTop(-halfHeight, Unit.PX);
	if (LocaleInfo.getCurrentLocale().isRTL()) {
	styles.right(0, Unit.PX);
	} else {
	styles.left(0, Unit.PX);
	}
	iconSafeHtml = template.iconWrapper(styles.toSafeStyles(), iconOnly);
	}
	}

	// Figure out the attributes.
	char accessKey = cell.getAccessKey();
	StringBuilder attributes = new StringBuilder();
	if (!cell.isEnabled()) {
	attributes.append("disabled=disabled ");
	}
	if (accessKey != 0) {
	attributes.append("accessKey=\"").append(SafeHtmlUtils.htmlEscape("" + accessKey));
	attributes.append("\" ");
	}

	// Create the button.
	SafeStylesBuilder styles = new SafeStylesBuilder();
	int iconWidth = (icon == null) ? 0 : icon.getWidth();
	int iconPadding = iconWidth + DEFAULT_ICON_PADDING;
	if (LocaleInfo.getCurrentLocale().isRTL()) {
	styles.paddingRight(iconPadding, Unit.PX);
	} else {
	styles.paddingLeft(iconPadding, Unit.PX);
	}
	SafeHtml safeValue = renderer.render(value);
	SafeHtml content = template.iconContentLayout(
	CommonResources.getInlineBlockStyle(), styles.toSafeStyles(), iconSafeHtml, safeValue);
	int tabIndex = cell.getTabIndex();
	StringBuilder openTag = new StringBuilder();
	openTag.append("<button type=\"button\"");
	openTag.append(" class=\"" + classes.toSafeHtml().asString() + "\"");
	openTag.append(" tabindex=\"" + tabIndex + "\" ");
	openTag.append(attributes.toString()).append(">");
	sb.append(SafeHtmlUtils.fromTrustedString(openTag.toString()));
	sb.append(content);
	sb.appendHtmlConstant("</button>");
	}

	@Override
	public void setFocus(Element parent, boolean focused) {
	Element focusable = parent.getFirstChildElement().cast();
	if (focused) {
	focusable.focus();
	} else {
	focusable.blur();
	}
	}
	}

	/**
	* The {@link NativePreviewHandler} used to unpush a button onmouseup, even if
	* the event doesn't occur over the button.
	*/
	private class UnpushHandler implements NativePreviewHandler {

	private final Element parent;
	private final HandlerRegistration reg;

	public UnpushHandler(Element parent) {
	this.parent = parent;
	this.reg = Event.addNativePreviewHandler(this);
	}

	@Override
	public void onPreviewNativeEvent(NativePreviewEvent event) {
	if (BrowserEvents.MOUSEUP.equals(event.getNativeEvent().getType())) {
	// Unregister self.
	reg.removeHandler();

	// Unpush the element.
	appearance.onUnpush(parent);
	}
	}
	}

	private char accessKey;
	private final Appearance<C> appearance;
	private Decoration decoration = Decoration.DEFAULT;
	private ImageResource icon;
	private boolean isCollapsedLeft;
	private boolean isCollapsedRight;
	private boolean isEnabled = true;

	/**
	* The tab index applied to the buttons. If the button is used in a list of
	* table, a tab index of -1 should be used so it doesn't interrupt the tab
	* sequence.
	*/
	private int tabIndex = -1;

	/**
	* Construct a new {@link ButtonCellBase} using the specified
	* {@link Appearance} to render the contents.
	*
	* @param appearance the appearance of the cell
	*/
	public ButtonCellBase(Appearance<C> appearance) {
	super(CLICK, KEYDOWN, MOUSEDOWN);
	this.appearance = appearance;
	}

	/**
	* Get the access key.
	*
	* @return the access key, or 0 if one is not defined
	*/
	public char getAccessKey() {
	return accessKey;
	}

	/**
	* Get the decoration style of the button.
	*/
	public Decoration getDecoration() {
	return decoration;
	}

	/**
	* Get the icon displayed next to the button text.
	*
	* @return the icon resource
	*/
	public ImageResource getIcon() {
	return icon;
	}

	/**
	* Return the tab index that is given to all rendered cells.
	*
	* @return the tab index
	*/
	public int getTabIndex() {
	return tabIndex;
	}

	@Override
	public boolean isCollapseLeft() {
	return this.isCollapsedLeft;
	}

	@Override
	public boolean isCollapseRight() {
	return this.isCollapsedRight;
	}

	@Override
	public boolean isEnabled() {
	return isEnabled;
	}

	@Override
	public void onBrowserEvent(Context context, Element parent, C value, NativeEvent event,
	ValueUpdater<C> valueUpdater) {
	// Ignore all events if disabled.
	if (!isEnabled()) {
	return;
	}

	// Let AbstractCell handle the enter key.
	super.onBrowserEvent(context, parent, value, event, valueUpdater);

	// Ignore events that occur outside of the button element.
	Element target = event.getEventTarget().cast();
	if (!parent.getFirstChildElement().isOrHasChild(target)) {
	return;
	}

	String eventType = event.getType();
	if (CLICK.equals(eventType)) {
	// Click the button.
	onEnterKeyDown(context, parent, value, event, valueUpdater);
	} else if (MOUSEDOWN.equals(eventType)) {
	// Push.
	appearance.onPush(parent);

	/*
	* Add a preview handler to unpush the button onmouseup or onblur, even if
	* the event doesn't occur over the button.
	*/
	new UnpushHandler(parent);

	// We will be handling all user visual feedback manually. Prevent browser
	// doing default handling (i.e. double-click highlights button text).
	event.preventDefault();
	}
	}

	@Override
	public void render(Context context, C value, SafeHtmlBuilder sb) {
	appearance.render(this, context, value, sb);
	}

	/**
	* Sets the cell's 'access key'. This key is used (in conjunction with a
	* browser-specific modifier key) to automatically focus the cell.
	*
	* <p>
	* The change takes effect the next time the Cell is rendered.
	*
	* @param key the cell's access key
	*/
	public void setAccessKey(char key) {
	this.accessKey = key;
	}

	/**
	* {@inheritDoc}
	*
	* <p>
	* The change takes effect the next time the Cell is rendered.
	*/
	@Override
	public void setCollapseLeft(boolean isCollapsed) {
	this.isCollapsedLeft = isCollapsed;
	}

	/**
	* {@inheritDoc}
	*
	* <p>
	* The change takes effect the next time the Cell is rendered.
	*/
	@Override
	public void setCollapseRight(boolean isCollapsed) {
	this.isCollapsedRight = isCollapsed;
	}

	/**
	* Set the {@link Decoration} of the button.
	*
	* <p>
	* This change takes effect the next time the cell is rendered.
	*
	* @param decoration the button decoration
	*/
	public void setDecoration(Decoration decoration) {
	this.decoration = decoration;
	}

	/**
	* {@inheritDoc}
	*
	* <p>
	* The change takes effect the next time the Cell is rendered.
	*/
	@Override
	public void setEnabled(boolean isEnabled) {
	this.isEnabled = isEnabled;
	}

	/**
	* Explicitly focus/unfocus this cell. Only one UI component can have focus at
	* a time, and the component that does will receive all keyboard events.
	*
	* @param parent the parent element
	* @param focused whether this cell should take focus or release it
	*/
	public void setFocus(Element parent, boolean focused) {
	appearance.setFocus(parent, focused);
	}

	/**
	* Set the icon to display next to the button text.
	*
	* @param icon the icon resource, or null not to show an icon
	*/
	public void setIcon(ImageResource icon) {
	this.icon = icon;
	}

	/**
	* Set the tab index to apply to the button. By default, the tab index is set
	* to -1 so that the button does not interrupt the tab chain when in a table
	* or list. The change takes effect the next time the Cell is rendered.
	*
	* @param tabIndex the tab index
	*/
	public void setTabIndex(int tabIndex) {
	this.tabIndex = tabIndex;
	}

	@Override
	protected void onEnterKeyDown(Context context, Element parent, C value, NativeEvent event,
	ValueUpdater<C> valueUpdater) {
	if (valueUpdater != null) {
	valueUpdater.update(value);
	}
	}
	}