C# と VB.NET の質問掲示板

こんばんは、倉田　有大です。

<UserControl x:Class="SkypeTRPGToolWPF.numericUpDown"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Height="25" Width="300">
    <Grid>
        <Grid.RowDefinitions>            
            <RowDefinition Height="*"/>            
            <RowDefinition Height="*"/>            
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <TextBlock FontSize="20" Grid.RowSpan="2" Name="textBlock1" Grid.ColumnSpan="2" />
        <Button Grid.Row="0" Grid.Column="1" Height ="Auto" HorizontalAlignment="Right" Margin="0" Name="button1" Width="23" Click="button1_Click" VerticalAlignment="Top">↑</Button>
        <Button Grid.Row="1" Grid.Column="1" Height ="Auto" HorizontalAlignment="Right" Name="button2" Width="23" VerticalAlignment="Bottom" Click="button2_Click">↓</Button>
        <Border BorderThickness="1" Grid.RowSpan="2" BorderBrush ="#FF7F9DB9" Width="auto" Height="Auto"/>
    </Grid>
</UserControl>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.ComponentModel;

namespace SkypeTRPGToolWPF
{
    /// <summary>
    /// numericUpDown.xaml の相互作用ロジック
    /// </summary>
    public partial class numericUpDown : UserControl, INotifyPropertyChanged
    {
        public static readonly DependencyProperty ValueProperty =
    DependencyProperty.Register("Value", typeof(int), typeof(numericUpDown));

        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName)
        {
            var h = PropertyChanged;
            if (h == null) return;

            h(this, new PropertyChangedEventArgs(propertyName));
        }

        private int _Value;
        public int Maximum
        {
            set;
            get;
        }
        public int Mininum
        {
            set;
            get;
        }
        public int Value
        {
            set
            {
                this.textBlock1.Text = value.ToString();
                _Value = value;
                OnPropertyChanged("Value");
                SetValue(ValueProperty, value);
            }
            get
            {
                return _Value;
            }
        }

        public numericUpDown()
        {
            Maximum = 100;
            Mininum = 0;            
            InitializeComponent();
            Value = 2;
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            if (Value < Maximum)
            {
                Value++;
                this.textBlock1.Text = Value.ToString();
            }
        }

        private void button2_Click(object sender, RoutedEventArgs e)
        {
            if (Value > Mininum)
            {
                Value--;
                this.textBlock1.Text = Value.ToString();
            }
        }
    }
}

上記のような、numericUpDownライクのコントロールを作成しました。
メインのウインドウに

<local:numericUpDown Value = "{Binding Path = DiceNum}" Width="auto" Grid.Row="2" Grid.Column="1" x:Name="numericUpDown1" />

上記のように貼り付けたのですが、ユーザーコントロールのPropertyChangedがnullのままでイベントが起こってくれません。
PropertyChangedにはどのタイミングで値が入るのでしょうか？