WPFで「ファイルを開く」ダイアログを裏から強制的に閉じる

CancelOpenFileDialogWPFSample.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Forms;
using System.Windows.Input;
using System.Windows.Interop;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using OpenFileDialog = Microsoft.Win32.OpenFileDialog;

namespace WpfApplication1
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            var openFileDialog1 = new OpenFileDialog();

            openFileDialog1.InitialDirectory = "c:\\";
            openFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
            openFileDialog1.FilterIndex = 2;
            openFileDialog1.RestoreDirectory = true;

            var dis = this.Dispatcher;
            Task.Run(async () =>
            {
                await Task.Delay(3000);
                await dis.InvokeAsync(() =>
                {
                    // モーダルでダイアログ表示されているけど裏の画面の描画は操作できる
                    lbl.Background = Brushes.Red;
                    SendKeys.SendWait("{ESC}");
                });
            });

            openFileDialog1.ShowDialog();
        }
    }
}