C# の素晴らしさを語る会 デモ用コード。 Install-Package PropertyChanged.Fody

MainWindow.xaml

<Window x:Class="FodyPractice.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <TextBox HorizontalAlignment="Left" Height="23" Margin="29,25,0,0" TextWrapping="Wrap" Text="{Binding FirstName}" VerticalAlignment="Top" Width="120"/>
        <TextBox HorizontalAlignment="Left" Height="23" Margin="199,25,0,0" TextWrapping="Wrap" Text="{Binding FamilyName}" VerticalAlignment="Top" Width="120"/>
        <TextBlock FontSize="40" HorizontalAlignment="Left" Margin="29,80,0,0" TextWrapping="Wrap" Text="{Binding DisplayName}" VerticalAlignment="Top" Height="60" Width="290"/>

    </Grid>
</Window>

MainWindow.xaml.cs

using System.Windows;

namespace FodyPractice
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            this.DataContext = new PersonViewModel
                {
                    FirstName = "Moriri",
                    FamilyName = "Rin"
                };
        }
    }
}

PersonViewModel.cs

using PropertyChanged;

namespace FodyPractice
{
    [ImplementPropertyChanged]
    public class PersonViewModel
    {
        public string FirstName { get; set; }
        public string FamilyName { get; set; }

        public string DisplayName
        {
            get { return string.Format("{0} {1}", FirstName, FamilyName); }
        }
    }
}

PersonViewModel.Modified.cs

using System;
using System.ComponentModel;

namespace FodyPractice
{
  public class PersonViewModel : INotifyPropertyChanged
	{
		public event PropertyChangedEventHandler PropertyChanged;
		public string FirstName
		{
			[CompilerGenerated]
			get
			{
				return this.<FirstName>k__BackingField;
			}
			[CompilerGenerated]
			set
			{
				if (string.Equals(this.<FirstName>k__BackingField, value, StringComparison.Ordinal))
				{
					return;
				}
				this.<FirstName>k__BackingField = value;
				this.OnPropertyChanged("DisplayName");
				this.OnPropertyChanged("FirstName");
			}
		}
		public string FamilyName
		{
			[CompilerGenerated]
			get
			{
				return this.<FamilyName>k__BackingField;
			}
			[CompilerGenerated]
			set
			{
				if (string.Equals(this.<FamilyName>k__BackingField, value, StringComparison.Ordinal))
				{
					return;
				}
				this.<FamilyName>k__BackingField = value;
				this.OnPropertyChanged("DisplayName");
				this.OnPropertyChanged("FamilyName");
			}
		}
		public string DisplayName
		{
			get
			{
				return string.Format("{0} {1}", this.FirstName, this.FamilyName);
			}
		}
		public virtual void OnPropertyChanged(string propertyName)
		{
			PropertyChangedEventHandler propertyChanged = this.PropertyChanged;
			if (propertyChanged != null)
			{
				propertyChanged(this, new PropertyChangedEventArgs(propertyName));
			}
		}
	}
}