C# と VB.NET の質問掲示板

VS2010 FW4.0 WPF

<Window x:Class="WpfApplication2.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" xmlns:my="clr-namespace:WpfApplication2">
    <Grid>
        <StackPanel>
            <Button Content="Exit" Name="button1" Width="100" Click="button1_Click" />
        </StackPanel>
        <my:UserControl1 Height="94"   x:Name="userControl11" Width="220" />
    </Grid>
</Window>

using System.Windows;
namespace WpfApplication2 {
    public partial class Window1 : Window {
        public Window1() {
            InitializeComponent();
        }

        private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e) {
            this.Visibility = Visibility.Hidden;
        }
    }
}

<UserControl x:Class="WpfApplication2.UserControl1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d"
             Unloaded="UserControl_Unloaded"
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <Button Content="SubWindowShow" Height="42" Name="button1"  Width="130" Click="button1_Click" />
    </Grid>
</UserControl>

using System.Windows;
using System.Windows.Controls;
namespace WpfApplication2 {
    public partial class UserControl1 : UserControl {

        Window1 _Window = new Window1();

        public UserControl1() {
            InitializeComponent();
        }

        private void button1_Click(object sender, RoutedEventArgs e) {
            _Window.Show();
        }

        private void UserControl_Unloaded(object sender, RoutedEventArgs e) {
            if (_Window == null) _Window.Close();
        }
    }
}

<Window x:Class="WpfApplication2.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Height="300" Width="300"
        WindowStyle="ToolWindow"
        Closing="Window_Closing"
        Topmost="True">
    <Grid>
        <Image Source="C:\Test.jpg"></Image>
    </Grid>
</Window>

using System.Windows;
namespace WpfApplication2 {
    public partial class Window1 : Window {
        public Window1() {
            InitializeComponent();
        }

        private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e) {
            this.Visibility = Visibility.Hidden;
        }
    }
}

UserControlから作成したWindowの破棄が出来ません。お知恵を貸して下さい