Visual Studio/WPF > Form > 닫힌 창을 다시 ShowModal() 했을 때 > Error:System.InvalidOperationException: 'Window가 닫힌 후 Visibility 설정, Show, ShowDialog 및 WindowInteropHelper.EnsureHandl 호출 수 없습니다. > 대처

Windows 7 Pro (32bit)
Microsoft Visual Studio 2017 Community

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

code

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.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace _170612_t1720_twoForms
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        private SubWindow subWin;
        public MainWindow()
        {
            InitializeComponent();
        }

        private void uxOpen_Click(object sender, RoutedEventArgs e)
        {
            if (subWin == null)
            {
                subWin = new SubWindow();
                subWin.Owner = this;
            }
            subWin.ShowDialog();
        }

        private void uxCheck_Click(object sender, RoutedEventArgs e)
        {
            if(subWin == null)
            {
                return;
            }
            string txt = subWin.uxName.Text;
            MessageBox.Show(txt);
        }
    }
}

<Window x:Class="_170612_t1720_twoForms.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:_170612_t1720_twoForms"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <StackPanel VerticalAlignment="Center">
            <Button Content="Open" x:Name="uxOpen"
                Height="28" Width="100"
                Click="uxOpen_Click"/>
            <Button Content="Check" x:Name="uxCheck"
                Height="28" Width="100"
                Click="uxCheck_Click"/>
        </StackPanel>
    </Grid>
</Window>

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.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;

namespace _170612_t1720_twoForms
{
    /// <summary>
    /// SubWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class SubWindow : Window
    {
        public SubWindow()
        {
            InitializeComponent();
        }

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

<Window x:Class="_170612_t1720_twoForms.SubWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:_170612_t1720_twoForms"
        mc:Ignorable="d"
        Title="SubWindow" Height="300" Width="300" Closing="Window_Closing">
    <Grid>
        <StackPanel>
            <TextBlock Text="Your Name"/>
            <TextBox x:Name="uxName" Width="200" Height="28"/>
        </StackPanel>
    </Grid>
</Window>