[WPF] 別スレッドで個別にイベントスレッドを起動して画面を表示 (SetWindowLong, Dispather.Run, Dispatcher.InvokeShutdown)

MainWindow.xaml.cs

// ReSharper disable PossibleInvalidOperationException
namespace WpfViewAnotherThread
{
    using System;
    using System.Diagnostics;
    using System.Runtime.InteropServices;
    using System.Threading;
    using System.Windows;
    using System.Windows.Interop;
    using System.Windows.Threading;

    public partial class MainWindow : Window
    {
        private const int GWL_HWNDPARENT = -8;

        private Thread _viewAThread;


        public MainWindow()
        {
            this.InitializeComponent();
        }

        public static IntPtr GetHandler(Window window)
        {
            var interop = new WindowInteropHelper(window);
            return interop.Handle;
        }

        public static void SetOwnerWindowMultithread(IntPtr windowHandleOwned, IntPtr intPtrOwner)
        {
            if (windowHandleOwned != IntPtr.Zero && intPtrOwner != IntPtr.Zero)
            {
                SetWindowLong(windowHandleOwned, GWL_HWNDPARENT, intPtrOwner.ToInt32());
            }
        }

        [DllImport("user32.dll")]
        private static extern int SetWindowLong(IntPtr hwnd, int index, int newStyle);

        private void BtnA_Click(object sender, RoutedEventArgs e)
        {
            if (this.ChkAnotherThread.IsChecked.Value)
            {
                var handler = GetHandler(this);
                this._viewAThread = new Thread(
                    state =>
                    {
                        var theType = (Type) state;
                        var win = (Window) Activator.CreateInstance(theType);
                        win.Closed += (o, args) =>
                        {
                            Dispatcher.CurrentDispatcher.InvokeShutdown();
                        };
                        win.Show();
                        SetOwnerWindowMultithread(GetHandler(win), handler);
                        Dispatcher.Run();
                    });

                this._viewAThread.IsBackground = true;
                this._viewAThread.SetApartmentState(ApartmentState.STA);
                this._viewAThread.Start(typeof(ViewA));
            }
            else
            {
                var win = new ViewA();
                win.ShowDialog();
            }
        }

        private void BtnB_Click(object sender, RoutedEventArgs e)
        {
            Debug.Assert(this._viewAThread.IsAlive == false);
        }
    }
}

MainWindow.xml

<Window x:Class="WpfViewAnotherThread.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>
        <Button x:Name="BtnA" Content="画面A" HorizontalAlignment="Left" Margin="10,10,0,0" VerticalAlignment="Top" Width="75" Click="BtnA_Click"/>
        <CheckBox x:Name="ChkAnotherThread" IsChecked="True" Content="別スレッドで表示" HorizontalAlignment="Left" Margin="11,39,0,0" VerticalAlignment="Top"/>
        <Button x:Name="BtnA_Copy" Content="画面A" HorizontalAlignment="Left" Margin="90,10,0,0" VerticalAlignment="Top" Width="75" Click="BtnB_Click"/>
    </Grid>
</Window>

ViewA.xaml.cs

namespace WpfViewAnotherThread
{
    using System.Windows;

    public partial class ViewA : Window
    {
        public ViewA()
        {
            this.InitializeComponent();
        }

        private void BtnShowSub_Click(object sender, RoutedEventArgs e)
        {
            var win = new ViewSub();
            win.Owner = this;
            win.ShowDialog();
        }
    }
}

ViewA.xml

<Window x:Class="WpfViewAnotherThread.ViewA"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="ViewA" Height="300" Width="300">
    <Grid>
        <TextBlock Text="ViewA" FontSize="40"></TextBlock>
        <Button x:Name="BtnShowSub" Content="サブ画面をShowDialog" HorizontalAlignment="Left" Margin="10,77,0,0" VerticalAlignment="Top" Width="Auto" Click="BtnShowSub_Click"/>
    </Grid>
</Window>