System.Windows.Controls.ItemContainerGenerator.IndexFromContainer C# (CSharp) Method

		public int IndexFromContainer (DependencyObject container)
		{
			int index;
			if (!ContainerIndexMap.TryMap (container, out index))
				index = -1;
			return index;
		}

        /// <summary>
        /// Sets focus to the next item in the ContextMenu.
        /// </summary>
        /// <param name="down">True to move the focus down; false to move it up.</param>
        private void FocusNextItem(bool down)
        {
            int      count           = Items.Count;
            int      startingIndex   = down ? -1 : count;
            MenuItem focusedMenuItem = FocusManager.GetFocusedElement() as MenuItem;

            if (null != focusedMenuItem && (this == focusedMenuItem.ParentMenuBase))
            {
                startingIndex = ItemContainerGenerator.IndexFromContainer(focusedMenuItem);
            }
            int index = startingIndex;

            do
            {
                index = (index + count + (down ? 1 : -1)) % count;
                MenuItem container = ItemContainerGenerator.ContainerFromIndex(index) as MenuItem;
                if (null != container)
                {
                    if (container.IsEnabled && container.Focus())
                    {
                        break;
                    }
                }
            }while (index != startingIndex);
        }