Conceptual Children: A powerful new concept in WPF

using System;
using System.Collections;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Media;

namespace WpfDiscipleBlogViewer3D
{
    /// <summary>
    /// Hosts an Viewport3D in the adorner layer above a Panel3D.
    /// </summary>
    public class Panel3DAdorner : Adorner
    {
        #region Data

        private ArrayList _logicalChildren;
        private readonly DockPanel _viewportHost = new DockPanel();

        #endregion // Data

        #region Constructor

        public Panel3DAdorner(Panel3D adornedPanel3D, Viewport3D viewport)
            : base(adornedPanel3D)
        {
            _viewportHost.Children.Add(viewport);
            _viewportHost.Background = Brushes.Transparent;
            base.AddLogicalChild(_viewportHost);
            base.AddVisualChild(_viewportHost);
        }

        #endregion // Constructor

        #region Measure/Arrange

        /// <summary>
        /// Allows the control to determine how big it wants to be.
        /// </summary>
        /// <param name="constraint">A limiting size for the control.</param>
        protected override Size MeasureOverride(Size constraint)
        {
            //_viewport.Measure(constraint);
            //return _viewport.DesiredSize;
            return constraint;
        }

        /// <summary>
        /// Positions and sizes the control.
        /// </summary>
        /// <param name="finalSize">The actual size of the control.</param>		
        protected override Size ArrangeOverride(Size finalSize)
        {
            Rect rect = new Rect(new Point(), finalSize);

            _viewportHost.Arrange(rect);

            return finalSize;
        }

        #endregion // Measure/Arrange

        #region Visual Children

        /// <summary>
        /// Required for the element to be rendered.
        /// </summary>
        protected override int VisualChildrenCount
        {
            get { return 1; }
        }

        /// <summary>
        /// Required for the element to be rendered.
        /// </summary>
        protected override Visual GetVisualChild(int index)
        {
            if (index != 0)
                throw new ArgumentOutOfRangeException("index");

            return _viewportHost;
        }

        #endregion // Visual Children

        #region Logical Children

        /// <summary>
        /// Required for the displayed element to inherit property values
        /// from the logical tree, such as FontSize.
        /// </summary>
        protected override IEnumerator LogicalChildren
        {
            get
            {
                if (_logicalChildren == null)
                {
                    _logicalChildren = new ArrayList();
                    _logicalChildren.Add(_viewportHost);
                }

                return _logicalChildren.GetEnumerator();
            }
        }

        #endregion // Logical Children
    }
}