WPF: A Beginner's Guide - Part 4 of n

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Shapes;
using System.Windows.Media;
using System.Windows.Media.Imaging;

namespace Attached_Properties_DPs
{
    /// <summary>
    /// A simply show case, to demonstrate a usage of an attached DP property.
    /// This example lets Windows add a header portion to the their default content
    /// with some new Contents. Kind of like using Master Pages in ASP .NET
    /// </summary>
    public class AttachedPropertyChildAdder
    {
        #region Register IsMasterHeaderApplied DP
        public static readonly DependencyProperty IsMasterHeaderAppliedProperty =
            DependencyProperty.RegisterAttached("IsMasterHeaderApplied",
                typeof(Boolean),
                typeof(AttachedPropertyChildAdder),
                new FrameworkPropertyMetadata(IsMasterHeaderAppliedChanged));

        public static void SetIsMasterHeaderApplied(DependencyObject element, Boolean value)
        {
            element.SetValue(IsMasterHeaderAppliedProperty, value);
        }
        public static Boolean GetIsMasterHeaderApplied(DependencyObject element)
        {
            return (Boolean)element.GetValue(IsMasterHeaderAppliedProperty);
        }
        #endregion

        #region PropertyChanged callback

        /// <summary>
        /// Is called whenever a user of the IsMasterHeaderApplied Attached DP changes
        /// the IsMasterHeaderApplied DP value 
        /// </summary>
        /// <param name="obj"></param>
        /// <param name="args"></param>
        public static void IsMasterHeaderAppliedChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
        {
            if ((bool)args.NewValue)
            {
                if (obj is Window)
                {
                    Window wnd = (Window)obj;
                    wnd.Loaded += new RoutedEventHandler(wnd_Loaded);
                }
            }
        }

        /// <summary>
        /// Hook into the Window load event to replace the Content of the Window
        /// with some custom Content, to show case exactly how cool DPs are.
        /// 
        /// In this example we are going to create a header for the Window.
        /// 
        /// So setting the IsMasterHeaderApplied will make sure the Window
        /// gets a header applied. 
        /// 
        /// Kind of like Master Pages in ASP .NET
        /// </summary>
        public static void wnd_Loaded(object sender, RoutedEventArgs e)
        {
            try
            {
                DockPanel dp = new DockPanel();
                dp.LastChildFill = true;
                StackPanel sp = new StackPanel();
                dp.Children.Add(sp);
                sp.Background = new SolidColorBrush(Colors.CornflowerBlue);
                sp.Orientation = Orientation.Vertical;
                sp.SetValue(DockPanel.DockProperty, Dock.Top);
                BitmapImage bitmap = new BitmapImage(new Uri("Images/Header.png", UriKind.Relative));
                Image image = new Image();
                image.Source = bitmap;
                sp.Children.Add(image);
                UIElement el = ((DependencyObject)sender as Window).Content as UIElement;
                el.SetValue(DockPanel.DockProperty, Dock.Bottom);
                ((DependencyObject)sender as Window).Content = null;
                dp.Children.Add(el);
               ((DependencyObject)sender as Window).Content = dp;
            }
            catch (Exception ex) 
            { 
                System.Diagnostics.Debug.WriteLine(string.Format("Exception : {}",ex.Message));  
            }
        }
        #endregion
    }
}