WPF.JoshSmith

// Copyright (C) Josh Smith - July 2006
using System;
using System.Globalization;
using System.Windows.Data;
using System.Xml;

namespace WPF.JoshSmith.Data.ValueConverters
{
    /// <summary>
    /// This value converter creates a .NET object from the XAML contained in an XmlElement.  The object
    /// created can be used as the content of a WPF control or ui element, such as the ContentPresenter.
    /// The inner xml of the XmlElement passed to the converter must contain valid XAML.
    /// </summary>
    [ValueConversion(typeof(XmlElement), typeof(object))]
    public class XamlToObjectConverter : IValueConverter
    {
        #region Data

        // Every call to the XamlReader requires a ParserContext, so a static instance is kept
        // to reduce the overhead of creating one every time a value is converted.
        private static System.Windows.Markup.ParserContext parserContext;

        #endregion // Data

        #region Static Constructor

        static XamlToObjectConverter()
        {
            // Initialize the parser context, which provides xml namespace mappings used when
            // the loose XAML is loaded and converted into a .NET object.
            parserContext = new System.Windows.Markup.ParserContext();
            parserContext.XmlnsDictionary.Add("", "http://schemas.microsoft.com/winfx/2006/xaml/presentation");
            parserContext.XmlnsDictionary.Add("x", "http://schemas.microsoft.com/winfx/2006/xaml");
        }

        #endregion // Static Constructor

        #region Convert

        object IValueConverter.Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            // The 'value' parameter must be an XmlElement.
            XmlElement elem = value as XmlElement;

            // We need to create a MemoryStream because the XamlReader requires a stream
            // from which the XAML is read.  
            using (System.IO.MemoryStream stream = new System.IO.MemoryStream())
            {
                // Convert the inner xml of the element into a byte array so
                // that it can be loaded into the memory stream.
                byte[] bytes = System.Text.Encoding.UTF8.GetBytes(elem.InnerXml);

                // Write the XAML element into the memory stream.
                stream.Write(bytes, 0, bytes.Length);

                // Reset the stream's current position back to the beginning so that when it
                // is read from, the reading will begin at the correct place.
                stream.Position = 0;

                // This is the magic method call which converts XAML into a .NET object.
                return System.Windows.Markup.XamlReader.Load(stream, parserContext);
            }
        }

        #endregion // Convert

        #region ConvertBack

        object IValueConverter.ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotSupportedException("ConvertBack not supported.");
        }

        #endregion // ConvertBack
    }
}