WPF DataGridのセルの内容を中央や右寄せで表示と編集をする

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;

namespace WpfDataGridAlignmentSample
{
    // アラインメントを指定できるDataGridTextColumnの拡張クラス
    public class DataGridTextColumnWithAlignment : DataGridTextColumn
    {
        // 依存関係プロパティ 垂直方向のアラインメント（デフォルトは中央）
        public VerticalAlignment VerticalAlignment
        {
            get { return (VerticalAlignment)GetValue(VerticalAlignmentProperty); }
            set { SetValue(VerticalAlignmentProperty, value); }
        }

        public static readonly DependencyProperty VerticalAlignmentProperty =
            DependencyProperty.Register("VerticalAlignment", 
                typeof(VerticalAlignment), typeof(DataGridTextColumnWithAlignment), new PropertyMetadata(VerticalAlignment.Center));


        // 依存関係プロパティ 水平方向のアラインメント（デフォルトは左）
        public HorizontalAlignment HorizontalAlignment
        {
            get { return (HorizontalAlignment)GetValue(HorizontalAlignmentProperty); }
            set { SetValue(HorizontalAlignmentProperty, value); }
        }

        public static readonly DependencyProperty HorizontalAlignmentProperty =
            DependencyProperty.Register("HorizontalAlignment", 
                typeof(HorizontalAlignment), typeof(DataGridTextColumnWithAlignment), new PropertyMetadata(HorizontalAlignment.Left));

        protected override FrameworkElement GenerateElement(DataGridCell cell, object dataItem)
        {
            // 未編集状態の時はTextBlock
            var tbl = base.GenerateElement(cell, dataItem) as TextBlock;

            if (tbl != null)
            {
                tbl.HorizontalAlignment = this.HorizontalAlignment;
                tbl.VerticalAlignment = this.VerticalAlignment;
                return tbl;
            }
            
            throw new NullReferenceException();
        }

        protected override FrameworkElement GenerateEditingElement(DataGridCell cell, object dataItem)
        {
            // 編集状態の時はTextBox
            var tb = base.GenerateEditingElement(cell, dataItem) as TextBox;

            if (tb != null)
            {
                tb.HorizontalAlignment = this.HorizontalAlignment;
                tb.VerticalAlignment = this.VerticalAlignment;
                return tb;
            }

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

    public class Person
    {
        public string ID { get; set; }
        public string LastName { get; set; }
        public string FirstName { get; set; }
        
        public Person(string ID, string LastName, string FirstName)
        {
            this.ID = ID;
            this.LastName = LastName;
            this.FirstName = FirstName;
        }
    }
    public class PersonCollection
    {
        private List<Person> _people = new List<Person>();
        public List<Person> People
        {
            get { return _people; }
        }
        public PersonCollection()
        {
            _people.Add(new Person("210000", "山田", "太郎"));
            _people.Add(new Person("210001", "鈴木", "花子"));
            _people.Add(new Person("210002", "畠山", "銀次"));
            _people.Add(new Person("210003", "青木", "健一"));
            _people.Add(new Person("210004", "多田野", "章宏"));
        }
    }
}

<Window x:Class="WpfDataGridAlignmentSample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:WpfDataGridAlignmentSample"
        Title="MainWindow" Height="250" Width="400">
    <Window.Resources>
        <!-- PersonCollectionクラスのインスタンス生成 -->
        <local:PersonCollection x:Key="objPersonCollection" />
    </Window.Resources>
    <Grid DataContext="{StaticResource objPersonCollection}">
            <DataGrid x:Name="MyDataGrid"
                  Grid.Row="0"
                  ItemsSource="{Binding People}"
                  AutoGenerateColumns="False" 
                  CanUserSortColumns="False" 
                  CanUserAddRows="False"
                  SelectionMode="Single" 
                  SelectionUnit="Cell">
                
                <DataGrid.ColumnHeaderStyle>
                    <Style TargetType="DataGridColumnHeader">
                        <Setter Property="Background" Value="DeepPink"/>
                        <Setter Property="Foreground" Value="White"/>
                        <Setter Property="FontWeight" Value="Bold"/>
                        <Setter Property="BorderThickness" Value="0,0,1,1"/>
                        <Setter Property="BorderBrush" Value="Black"/>
                        <Setter Property="HorizontalContentAlignment" Value="Center"/>
                        <Setter Property="VerticalContentAlignment"   Value="Center"/>
                    </Style>
                </DataGrid.ColumnHeaderStyle>
                <DataGrid.Columns>
                    <local:DataGridTextColumnWithAlignment Header="社員番号" Binding="{Binding ID}" HorizontalAlignment="Right" Width="100" CanUserSort="False" />
                    <local:DataGridTextColumnWithAlignment Header="姓" Binding="{Binding LastName}" HorizontalAlignment="Center" Width="120" IsReadOnly="True" CanUserSort="False" />
                    <local:DataGridTextColumnWithAlignment Header="名" Binding="{Binding FirstName}" HorizontalAlignment="Center" Width="*" IsReadOnly="True" CanUserSort="False" />
                </DataGrid.Columns>
            </DataGrid>
    </Grid>
</Window>