text: // Copyright 2007 The Closure Library Authors. All Rights Reserved.
  //
  // 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.
  
  /**
   * @fileoverview A menu button control.
   *
   * @see ../demos/menubutton.html
   */
  
  goog.provide('goog.ui.MenuButton');
  
  goog.require('goog.Timer');
  goog.require('goog.dom');
  goog.require('goog.dom.a11y');
  goog.require('goog.dom.a11y.State');
  goog.require('goog.events.EventType');
  goog.require('goog.events.KeyCodes');
  goog.require('goog.events.KeyHandler.EventType');
  goog.require('goog.math.Box');
  goog.require('goog.math.Rect');
  goog.require('goog.positioning.Corner');
  goog.require('goog.positioning.MenuAnchoredPosition');
  goog.require('goog.style');
  goog.require('goog.ui.Button');
  goog.require('goog.ui.Component.EventType');
  goog.require('goog.ui.Component.State');
  goog.require('goog.ui.ControlContent');
  goog.require('goog.ui.Menu');
  goog.require('goog.ui.MenuButtonRenderer');
  goog.require('goog.ui.registry');
  goog.require('goog.userAgent');
  goog.require('goog.userAgent.product');
  
  
  
  /**
   * A menu button control.  Extends {@link goog.ui.Button} by composing a button
   * with a dropdown arrow and a popup menu.
   *
   * @param {goog.ui.ControlContent} content Text caption or existing DOM
   *     structure to display as the button's caption (if any).
   * @param {goog.ui.Menu=} opt_menu Menu to render under the button when clicked.
   * @param {goog.ui.ButtonRenderer=} opt_renderer Renderer used to render or
   *     decorate the menu button; defaults to {@link goog.ui.MenuButtonRenderer}.
   * @param {goog.dom.DomHelper=} opt_domHelper Optional DOM hepler, used for
   *     document interaction.
   * @constructor
   * @extends {goog.ui.Button}
   */
  goog.ui.MenuButton = function(content, opt_menu, opt_renderer, opt_domHelper) {
    goog.ui.Button.call(this, content, opt_renderer ||
        goog.ui.MenuButtonRenderer.getInstance(), opt_domHelper);
  
    // Menu buttons support the OPENED state.
    this.setSupportedState(goog.ui.Component.State.OPENED, true);
  
    if (opt_menu) {
      this.setMenu(opt_menu);
    }
    this.menuMargin_ = null;
    this.timer_ = new goog.Timer(500);  // 0.5 sec
  
    // Phones running iOS prior to version 4.2.
    if ((goog.userAgent.product.IPHONE || goog.userAgent.product.IPAD) &&
        // Check the webkit version against the version for iOS 4.2.1.
        !goog.userAgent.isVersion('533.17.9')) {
      // @bug 4322060 This is required so that the menu works correctly on
      // iOS prior to version 4.2. Otherwise, the blur action closes the menu
      // before the menu button click can be processed.
      this.setFocusablePopupMenu(true);
    }
  };
  goog.inherits(goog.ui.MenuButton, goog.ui.Button);
  
  
  /**
   * The menu.
   * @type {goog.ui.Menu|undefined}
   * @private
   */
  goog.ui.MenuButton.prototype.menu_;
  
  
  /**
   * The position element.  If set, use positionElement_ to position the
   * popup menu instead of the default which is to use the menu button element.
   * @type {Element|undefined}
   * @private
   */
  goog.ui.MenuButton.prototype.positionElement_;
  
  
  /**
   * The margin to apply to the menu's position when it is shown.  If null, no
   * margin will be applied.
   * @type {goog.math.Box}
   * @private
   */
  goog.ui.MenuButton.prototype.menuMargin_;
  
  
  /**
   * Whether the popup menu should be aligned to the start or the end of the
   * button; defaults to true (align to start).
   * @type {boolean}
   * @private
   */
  goog.ui.MenuButton.prototype.alignToStart_ = true;
  
  
  /**
   * Whether the popup menu should scroll when it's to big to fit vertically
   * on the screen. Defaults to false, use the adjust logic to reposition the
   * menu on overflow rather then scroll.
   * @type {boolean}
   * @private
   */
  goog.ui.MenuButton.prototype.scrollOnOverflow_ = false;
  
  
  /**
   * Whether the attached popup menu is focusable or not (defaults to false).
   * Popup menus attached to menu buttons usually don't need to be focusable,
   * i.e. the button retains keyboard focus, and forwards key events to the
   * menu for processing.  However, menus like {@link goog.ui.FilteredMenu}
   * need to be focusable.
   * @type {boolean}
   * @private
   */
  goog.ui.MenuButton.prototype.isFocusablePopupMenu_ = false;
  
  
  /**
   * A Timer to correct menu position.
   * @type {goog.Timer}
   * @private
   */
  goog.ui.MenuButton.prototype.timer_;
  
  
  /**
   * The bounding rectangle of the button element.
   * @type {goog.math.Rect}
   * @private
   */
  goog.ui.MenuButton.prototype.buttonRect_;
  
  
  /**
   * The viewport rectangle.
   * @type {goog.math.Box}
   * @private
   */
  goog.ui.MenuButton.prototype.viewportBox_;
  
  
  /**
   * The original size.
   * @type {goog.math.Size|undefined}
   * @private
   */
  goog.ui.MenuButton.prototype.originalSize_;
  
  
  /**
   * Do we render the drop down menu as a sibling to the label, or at the end
   * of the current dom?
   * @type {boolean}
   * @private
   */
  goog.ui.MenuButton.prototype.renderMenuAsSibling_ = false;
  
  
  /**
   * Sets up event handlers specific to menu buttons.
   * @override
   */
  goog.ui.MenuButton.prototype.enterDocument = function() {
    goog.ui.MenuButton.superClass_.enterDocument.call(this);
    if (this.menu_) {
      this.attachMenuEventListeners_(this.menu_, true);
    }
    goog.dom.a11y.setState(this.getElement(),
        goog.dom.a11y.State.HASPOPUP, 'true');
  };
  
  
  /**
   * Removes event handlers specific to menu buttons, and ensures that the
   * attached menu also exits the document.
   * @override
   */
  goog.ui.MenuButton.prototype.exitDocument = function() {
    goog.ui.MenuButton.superClass_.exitDocument.call(this);
    if (this.menu_) {
      this.setOpen(false);
      this.menu_.exitDocument();
      this.attachMenuEventListeners_(this.menu_, false);
  
      var menuElement = this.menu_.getElement();
      if (menuElement) {
        goog.dom.removeNode(menuElement);
      }
    }
  };
  
  
  /** @override */
  goog.ui.MenuButton.prototype.disposeInternal = function() {
    goog.ui.MenuButton.superClass_.disposeInternal.call(this);
    if (this.menu_) {
      this.menu_.dispose();
      delete this.menu_;
    }
    delete this.positionElement_;
    this.timer_.dispose();
  };
  
  
  /**
   * Handles mousedown events.  Invokes the superclass implementation to dispatch
   * an ACTIVATE event and activate the button.  Also toggles the visibility of
   * the attached menu.
   * @param {goog.events.Event} e Mouse event to handle.
   * @override
   * @protected
   */
  goog.ui.MenuButton.prototype.handleMouseDown = function(e) {
    goog.ui.MenuButton.superClass_.handleMouseDown.call(this, e);
    if (this.isActive()) {
      // The component was allowed to activate; toggle menu visibility.
      this.setOpen(!this.isOpen(), e);
      if (this.menu_) {
        this.menu_.setMouseButtonPressed(this.isOpen());
      }
    }
  };
  
  
  /**
   * Handles mouseup events.  Invokes the superclass implementation to dispatch
   * an ACTION event and deactivate the button.
   * @param {goog.events.Event} e Mouse event to handle.
   * @override
   * @protected
   */
  goog.ui.MenuButton.prototype.handleMouseUp = function(e) {
    goog.ui.MenuButton.superClass_.handleMouseUp.call(this, e);
    if (this.menu_ && !this.isActive()) {
      this.menu_.setMouseButtonPressed(false);
    }
  };
  
  
  /**
   * Performs the appropriate action when the menu button is activated by the
   * user.  Overrides the superclass implementation by not dispatching an {@code
   * ACTION} event, because menu buttons exist only to reveal menus, not to
   * perform actions themselves.  Calls {@link #setActive} to deactivate the
   * button.
   * @param {goog.events.Event} e Mouse or key event that triggered the action.
   * @return {boolean} Whether the action was allowed to proceed.
   * @override
   * @protected
   */
  goog.ui.MenuButton.prototype.performActionInternal = function(e) {
    this.setActive(false);
    return true;
  };
  
  
  /**
   * Handles mousedown events over the document.  If the mousedown happens over
   * an element unrelated to the component, hides the menu.
   * TODO(user): Reconcile this with goog.ui.Popup (and handle frames/windows).
   * @param {goog.events.BrowserEvent} e Mouse event to handle.
   * @protected
   */
  goog.ui.MenuButton.prototype.handleDocumentMouseDown = function(e) {
    if (this.menu_ &&
        this.menu_.isVisible() &&
        !this.containsElement(/** @type {Element} */ (e.target))) {
      // User clicked somewhere else in the document while the menu was visible;
      // dismiss menu.
      this.setOpen(false);
    }
  };
  
  
  /**
   * Returns true if the given element is to be considered part of the component,
   * even if it isn't a DOM descendant of the component's root element.
   * @param {Element} element Element to test (if any).
   * @return {boolean} Whether the element is considered part of the component.
   * @protected
   */
  goog.ui.MenuButton.prototype.containsElement = function(element) {
    return element && goog.dom.contains(this.getElement(), element) ||
        this.menu_ && this.menu_.containsElement(element) || false;
  };
  
  
  /** @override */
  goog.ui.MenuButton.prototype.handleKeyEventInternal = function(e) {
    // Handle SPACE on keyup and all other keys on keypress.
    if (e.keyCode == goog.events.KeyCodes.SPACE) {
      // Prevent page scrolling in Chrome.
      e.preventDefault();
      if (e.type != goog.events.EventType.KEYUP) {
        return false;
      }
    } else if (e.type != goog.events.KeyHandler.EventType.KEY) {
      return false;
    }
  
    if (this.menu_ && this.menu_.isVisible()) {
      // Menu is open.
      var handledByMenu = this.menu_.handleKeyEvent(e);
      if (e.keyCode == goog.events.KeyCodes.ESC) {
        // Dismiss the menu.
        this.setOpen(false);
        return true;
      }
      return handledByMenu;
    }
  
    if (e.keyCode == goog.events.KeyCodes.DOWN ||
        e.keyCode == goog.events.KeyCodes.UP ||
        e.keyCode == goog.events.KeyCodes.SPACE) {
      // Menu is closed, and the user hit the down/up/space key; open menu.
      this.setOpen(true);
      return true;
    }
  
    // Key event wasn't handled by the component.
    return false;
  };
  
  
  /**
   * Handles {@code ACTION} events dispatched by an activated menu item.
   * @param {goog.events.Event} e Action event to handle.
   * @protected
   */
  goog.ui.MenuButton.prototype.handleMenuAction = function(e) {
    // Close the menu on click.
    this.setOpen(false);
  };
  
  
  /**
   * Handles {@code BLUR} events dispatched by the popup menu by closing it.
   * Only registered if the menu is focusable.
   * @param {goog.events.Event} e Blur event dispatched by a focusable menu.
   */
  goog.ui.MenuButton.prototype.handleMenuBlur = function(e) {
    // Close the menu when it reports that it lost focus, unless the button is
    // pressed (active).
    if (!this.isActive()) {
      this.setOpen(false);
    }
  };
  
  
  /**
   * Handles blur events dispatched by the button's key event target when it
   * loses keyboard focus by closing the popup menu (unless it is focusable).
   * Only registered if the button is focusable.
   * @param {goog.events.Event} e Blur event dispatched by the menu button.
   * @override
   * @protected
   */
  goog.ui.MenuButton.prototype.handleBlur = function(e) {
    if (!this.isFocusablePopupMenu()) {
      this.setOpen(false);
    }
    goog.ui.MenuButton.superClass_.handleBlur.call(this, e);
  };
  
  
  /**
   * Returns the menu attached to the button.  If no menu is attached, creates a
   * new empty menu.
   * @return {goog.ui.Menu} Popup menu attached to the menu button.
   */
  goog.ui.MenuButton.prototype.getMenu = function() {
    if (!this.menu_) {
      this.setMenu(new goog.ui.Menu(this.getDomHelper()));
    }
    return this.menu_ || null;
  };
  
  
  /**
   * Replaces the menu attached to the button with the argument, and returns the
   * previous menu (if any).
   * @param {goog.ui.Menu?} menu New menu to be attached to the menu button (null
   *     to remove the menu).
   * @return {goog.ui.Menu|undefined} Previous menu (undefined if none).
   */
  goog.ui.MenuButton.prototype.setMenu = function(menu) {
    var oldMenu = this.menu_;
  
    // Do nothing unless the new menu is different from the current one.
    if (menu != oldMenu) {
      if (oldMenu) {
        this.setOpen(false);
        if (this.isInDocument()) {
          this.attachMenuEventListeners_(oldMenu, false);
        }
        delete this.menu_;
      }
      if (menu) {
        this.menu_ = menu;
        menu.setParent(this);
        menu.setVisible(false);
        menu.setAllowAutoFocus(this.isFocusablePopupMenu());
        if (this.isInDocument()) {
          this.attachMenuEventListeners_(menu, true);
        }
      }
    }
  
    return oldMenu;
  };
  
  
  /**
   * Sets an element for anchoring the menu.
   * @param {Element} positionElement New element to use for
   *     positioning the dropdown menu.  Null to use the default behavior
   *     of positioning to this menu button.
   */
  goog.ui.MenuButton.prototype.setPositionElement = function(
      positionElement) {
    this.positionElement_ = positionElement;
    this.positionMenu();
  };
  
  
  /**
   * Sets a margin that will be applied to the menu's position when it is shown.
   * If null, no margin will be applied.
   * @param {goog.math.Box} margin Margin to apply.
   */
  goog.ui.MenuButton.prototype.setMenuMargin = function(margin) {
    this.menuMargin_ = margin;
  };
  
  
  /**
   * Adds a new menu item at the end of the menu.
   * @param {goog.ui.MenuItem|goog.ui.MenuSeparator|goog.ui.Control} item Menu
   *     item to add to the menu.
   */
  goog.ui.MenuButton.prototype.addItem = function(item) {
    this.getMenu().addChild(item, true);
  };
  
  
  /**
   * Adds a new menu item at the specific index in the menu.
   * @param {goog.ui.MenuItem|goog.ui.MenuSeparator} item Menu item to add to the
   *     menu.
   * @param {number} index Index at which to insert the menu item.
   */
  goog.ui.MenuButton.prototype.addItemAt = function(item, index) {
    this.getMenu().addChildAt(item, index, true);
  };
  
  
  /**
   * Removes the item from the menu and disposes of it.
   * @param {goog.ui.MenuItem|goog.ui.MenuSeparator} item The menu item to remove.
   */
  goog.ui.MenuButton.prototype.removeItem = function(item) {
    var child = this.getMenu().removeChild(item, true);
    if (child) {
      child.dispose();
    }
  };
  
  
  /**
   * Removes the menu item at a given index in the menu and disposes of it.
   * @param {number} index Index of item.
   */
  goog.ui.MenuButton.prototype.removeItemAt = function(index) {
    var child = this.getMenu().removeChildAt(index, true);
    if (child) {
      child.dispose();
    }
  };
  
  
  /**
   * Returns the menu item at a given index.
   * @param {number} index Index of menu item.
   * @return {goog.ui.MenuItem?} Menu item (null if not found).
   */
  goog.ui.MenuButton.prototype.getItemAt = function(index) {
    return this.menu_ ?
        /** @type {goog.ui.MenuItem} */ (this.menu_.getChildAt(index)) : null;
  };
  
  
  /**
   * Returns the number of items in the menu (including separators).
   * @return {number} The number of items in the menu.
   */
  goog.ui.MenuButton.prototype.getItemCount = function() {
    return this.menu_ ? this.menu_.getChildCount() : 0;
  };
  
  
  /**
   * Shows/hides the menu button based on the value of the argument.  Also hides
   * the popup menu if the button is being hidden.
   * @param {boolean} visible Whether to show or hide the button.
   * @param {boolean=} opt_force If true, doesn't check whether the component
   *     already has the requested visibility, and doesn't dispatch any events.
   * @return {boolean} Whether the visibility was changed.
   * @override
   */
  goog.ui.MenuButton.prototype.setVisible = function(visible, opt_force) {
    var visibilityChanged = goog.ui.MenuButton.superClass_.setVisible.call(this,
        visible, opt_force);
    if (visibilityChanged && !this.isVisible()) {
      this.setOpen(false);
    }
    return visibilityChanged;
  };
  
  
  /**
   * Enables/disables the menu button based on the value of the argument, and
   * updates its CSS styling.  Also hides the popup menu if the button is being
   * disabled.
   * @param {boolean} enable Whether to enable or disable the button.
   * @override
   */
  goog.ui.MenuButton.prototype.setEnabled = function(enable) {
    goog.ui.MenuButton.superClass_.setEnabled.call(this, enable);
    if (!this.isEnabled()) {
      this.setOpen(false);
    }
  };
  
  
  /**
   * @return {boolean} Whether the menu is aligned to the start of the button
   *     (left if the render direction is left-to-right, right if the render
   *     direction is right-to-left).
   */
  goog.ui.MenuButton.prototype.isAlignMenuToStart = function() {
    return this.alignToStart_;
  };
  
  
  /**
   * Sets whether the menu is aligned to the start or the end of the button.
   * @param {boolean} alignToStart Whether the menu is to be aligned to the start
   *     of the button (left if the render direction is left-to-right, right if
   *     the render direction is right-to-left).
   */
  goog.ui.MenuButton.prototype.setAlignMenuToStart = function(alignToStart) {
    this.alignToStart_ = alignToStart;
  };
  
  
  /**
   * Sets whether the menu should scroll when it's too big to fix vertically on
   * the screen.  The css of the menu element should have overflow set to auto.
   * Note: Adding or removing items while the menu is open will not work correctly
   * if scrollOnOverflow is on.
   * @param {boolean} scrollOnOverflow Whether the menu should scroll when too big
   *     to fit on the screen.  If false, adjust logic will be used to try and
   *     reposition the menu to fit.
   */
  goog.ui.MenuButton.prototype.setScrollOnOverflow = function(scrollOnOverflow) {
    this.scrollOnOverflow_ = scrollOnOverflow;
  };
  
  
  /**
   * @return {boolean} Wether the menu will scroll when it's to big to fit
   *     vertically on the screen.
   */
  goog.ui.MenuButton.prototype.isScrollOnOverflow = function() {
    return this.scrollOnOverflow_;
  };
  
  
  /**
   * @return {boolean} Whether the attached menu is focusable.
   */
  goog.ui.MenuButton.prototype.isFocusablePopupMenu = function() {
    return this.isFocusablePopupMenu_;
  };
  
  
  /**
   * Sets whether the attached popup menu is focusable.  If the popup menu is
   * focusable, it may steal keyboard focus from the menu button, so the button
   * will not hide the menu on blur.
   * @param {boolean} focusable Whether the attached menu is focusable.
   */
  goog.ui.MenuButton.prototype.setFocusablePopupMenu = function(focusable) {
    // TODO(user):  The menu itself should advertise whether it is focusable.
    this.isFocusablePopupMenu_ = focusable;
  };
  
  
  /**
   * Sets whether to render the menu as a sibling element of the button.
   * Normally, the menu is a child of document.body.  This option is useful if
   * you need the menu to inherit styles from a common parent element, or if you
   * otherwise need it to share a parent element for desired event handling.  One
   * example of the latter is if the parent is in a goog.ui.Popup, to ensure that
   * clicks on the menu are considered being within the popup.
   * @param {boolean} renderMenuAsSibling Whether we render the menu at the end
   *     of the dom or as a sibling to the button/label that renders the drop
   *     down.
   */
  goog.ui.MenuButton.prototype.setRenderMenuAsSibling = function(
      renderMenuAsSibling) {
    this.renderMenuAsSibling_ = renderMenuAsSibling;
  };
  
  
  /**
   * Reveals the menu and hooks up menu-specific event handling.
   * @deprecated Use {@link #setOpen} instead.
   */
  goog.ui.MenuButton.prototype.showMenu = function() {
    this.setOpen(true);
  };
  
  
  /**
   * Hides the menu and cleans up menu-specific event handling.
   * @deprecated Use {@link #setOpen} instead.
   */
  goog.ui.MenuButton.prototype.hideMenu = function() {
    this.setOpen(false);
  };
  
  
  /**
   * Opens or closes the attached popup menu.
   * @param {boolean} open Whether to open or close the menu.
   * @param {goog.events.Event=} opt_e Mousedown event that caused the menu to
   *     be opened.
   * @override
   */
  goog.ui.MenuButton.prototype.setOpen = function(open, opt_e) {
    goog.ui.MenuButton.superClass_.setOpen.call(this, open);
    if (this.menu_ && this.hasState(goog.ui.Component.State.OPENED) == open) {
      if (open) {
        if (!this.menu_.isInDocument()) {
          if (this.renderMenuAsSibling_) {
            this.menu_.render(/** @type {Element} */ (
                this.getElement().parentNode));
          } else {
            this.menu_.render();
          }
        }
        this.viewportBox_ =
            goog.style.getVisibleRectForElement(this.getElement());
        this.buttonRect_ = goog.style.getBounds(this.getElement());
        this.positionMenu();
        this.menu_.setHighlightedIndex(-1);
      } else {
        this.setActive(false);
        this.menu_.setMouseButtonPressed(false);
  
        // Clear any remaining a11y state.
        if (this.getElement()) {
          goog.dom.a11y.setState(this.getElement(),
              goog.dom.a11y.State.ACTIVEDESCENDANT, '');
        }
  
        // Clear any sizes that might have been stored.
        if (goog.isDefAndNotNull(this.originalSize_)) {
          this.originalSize_ = undefined;
          var elem = this.menu_.getElement();
          if (elem) {
            goog.style.setSize(elem, '', '');
          }
        }
      }
      this.menu_.setVisible(open, false, opt_e);
      // In Pivot Tables the menu button somehow gets disposed of during the
      // setVisible call, causing attachPopupListeners_ to fail.
      // TODO(user): Debug what happens.
      if (!this.isDisposed()) {
        this.attachPopupListeners_(open);
      }
    }
  };
  
  
  /**
   * Positions the menu under the button.  May be called directly in cases when
   * the menu size is known to change.
   */
  goog.ui.MenuButton.prototype.positionMenu = function() {
    if (!this.menu_.isInDocument()) {
      return;
    }
  
    var positionElement = this.positionElement_ || this.getElement();
  
    var anchorCorner = this.isAlignMenuToStart() ?
        goog.positioning.Corner.BOTTOM_START : goog.positioning.Corner.BOTTOM_END;
    var position = new goog.positioning.MenuAnchoredPosition(positionElement,
        anchorCorner, /* opt_adjust */ !this.scrollOnOverflow_,
        /* opt_resize */ this.scrollOnOverflow_);
  
    var elem = this.menu_.getElement();
    if (!this.menu_.isVisible()) {
      elem.style.visibility = 'hidden';
      goog.style.showElement(elem, true);
    }
  
    if (!this.originalSize_ && this.scrollOnOverflow_) {
      this.originalSize_ = goog.style.getSize(elem);
    }
    var popupCorner = this.isAlignMenuToStart() ?
        goog.positioning.Corner.TOP_START : goog.positioning.Corner.TOP_END;
    position.reposition(elem, popupCorner, this.menuMargin_, this.originalSize_);
  
    if (!this.menu_.isVisible()) {
      goog.style.showElement(elem, false);
      elem.style.visibility = 'visible';
    }
  };
  
  
  /**
   * Periodically repositions the menu while it is visible.
   *
   * @param {goog.events.Event} e An event object.
   * @private
   */
  goog.ui.MenuButton.prototype.onTick_ = function(e) {
    // Call positionMenu() only if the button position or size was
    // changed, or if the window's viewport was changed.
    var currentButtonRect = goog.style.getBounds(this.getElement());
    var currentViewport = goog.style.getVisibleRectForElement(this.getElement());
    if (!goog.math.Rect.equals(this.buttonRect_, currentButtonRect) ||
        !goog.math.Box.equals(this.viewportBox_, currentViewport)) {
      this.buttonRect_ = currentButtonRect;
      this.viewportBox_ = currentViewport;
      this.positionMenu();
    }
  };
  
  
  /**
   * Attaches or detaches menu event listeners to/from the given menu.
   * Called each time a menu is attached to or detached from the button.
   * @param {goog.ui.Menu} menu Menu on which to listen for events.
   * @param {boolean} attach Whether to attach or detach event listeners.
   * @private
   */
  goog.ui.MenuButton.prototype.attachMenuEventListeners_ = function(menu,
      attach) {
    var handler = this.getHandler();
    var method = attach ? handler.listen : handler.unlisten;
  
    // Handle events dispatched by menu items.
    method.call(handler, menu, goog.ui.Component.EventType.ACTION,
        this.handleMenuAction);
    method.call(handler, menu, goog.ui.Component.EventType.HIGHLIGHT,
        this.handleHighlightItem);
    method.call(handler, menu, goog.ui.Component.EventType.UNHIGHLIGHT,
        this.handleUnHighlightItem);
  };
  
  
  /**
   * Handles {@code HIGHLIGHT} events dispatched by the attached menu.
   * @param {goog.events.Event} e Highlight event to handle.
   */
  goog.ui.MenuButton.prototype.handleHighlightItem = function(e) {
    goog.dom.a11y.setState(this.getElement(),
        goog.dom.a11y.State.ACTIVEDESCENDANT, e.target.getElement().id);
  };
  
  
  /**
   * Handles UNHIGHLIGHT events dispatched by the associated menu.
   * @param {goog.events.Event} e Unhighlight event to handle.
   */
  goog.ui.MenuButton.prototype.handleUnHighlightItem = function(e) {
    if (!this.menu_.getHighlighted()) {
      goog.dom.a11y.setState(this.getElement(),
          goog.dom.a11y.State.ACTIVEDESCENDANT, '');
    }
  };
  
  
  /**
   * Attaches or detaches event listeners depending on whether the popup menu
   * is being shown or hidden.  Starts listening for document mousedown events
   * and for menu blur events when the menu is shown, and stops listening for
   * these events when it is hidden.  Called from {@link #setOpen}.
   * @param {boolean} attach Whether to attach or detach event listeners.
   * @private
   */
  goog.ui.MenuButton.prototype.attachPopupListeners_ = function(attach) {
    var handler = this.getHandler();
    var method = attach ? handler.listen : handler.unlisten;
  
    // Listen for document mousedown events in the capture phase, because
    // the target may stop propagation of the event in the bubble phase.
    method.call(handler, this.getDomHelper().getDocument(),
        goog.events.EventType.MOUSEDOWN, this.handleDocumentMouseDown, true);
  
    // Only listen for blur events dispatched by the menu if it is focusable.
    if (this.isFocusablePopupMenu()) {
      method.call(handler, /** @type {goog.events.EventTarget} */ (this.menu_),
          goog.ui.Component.EventType.BLUR, this.handleMenuBlur);
    }
  
    method.call(handler, this.timer_, goog.Timer.TICK, this.onTick_);
    if (attach) {
      this.timer_.start();
    } else {
      this.timer_.stop();
    }
  };
  
  
  // Register a decorator factory function for goog.ui.MenuButtons.
  goog.ui.registry.setDecoratorByClassName(goog.ui.MenuButtonRenderer.CSS_CLASS,
      function() {
        // MenuButton defaults to using MenuButtonRenderer.
        return new goog.ui.MenuButton(null);
      });
  