Catel - Part 4 of n: Unit testing with Catel

// --------------------------------------------------------------------------------------------------------------------
// <copyright file="VisualWrapper.cs" company="Catel development team">
//   Copyright (c) 2008 - 2011 Catel development team. All rights reserved.
// </copyright>
// <summary>
//   This visual wrapper is used by VisualTargetPresentationSource
// </summary>
// --------------------------------------------------------------------------------------------------------------------

using System;
using System.Windows;
using System.Windows.Markup;
using System.Windows.Media;

namespace Catel.Windows.Controls
{
	/// <summary>
	/// This visual wrapper is used by VisualTargetPresentationSource
	/// </summary>
	[ContentProperty("Child")]
	public class VisualWrapper : FrameworkElement
	{
		private Visual _child;

		/// <summary>
		/// Gets or sets the child.
		/// </summary>
		/// <value>The child.</value>
		public Visual Child
		{
			get
			{
			    return _child;
			}

			set
			{
				if (_child != null)
				{
					RemoveVisualChild(_child);
				}

				_child = value;

				if (_child != null)
				{
					AddVisualChild(_child);
				}
			}
		}

		/// <summary>
		/// Overrides <see cref="M:System.Windows.Media.Visual.GetVisualChild(System.Int32)"/>, and returns a child at the specified index from a collection of child elements.
		/// </summary>
		/// <param name="index">The zero-based index of the requested child element in the collection.</param>
		/// <returns>
		/// The requested child element. This should not return null; if the provided index is out of range, an exception is thrown.
		/// </returns>
		protected override Visual GetVisualChild(int index)
		{
			if (_child != null && index == 0)
			{
				return _child;
			}
			
			throw new ArgumentOutOfRangeException("index");
		}

		/// <summary>
		/// Gets the number of visual child elements within this element.
		/// </summary>
		/// <value></value>
		/// <returns>
		/// The number of visual child elements for this element.
		/// </returns>
		protected override int VisualChildrenCount
		{
			get { return _child != null ? 1 : 0; }
		}
	}
}