wpf: split grid vertical/horizontal

Window00.xaml

<Window x:Class="wpf_testproj.Window00"
        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:wpf_testproj"
        mc:Ignorable="d"
        Title="Window00" Height="600" Width="600"
        PreviewKeyDown="Window_PreviewKeyDown">
    <Grid x:Name="root_grid">
        <Grid>
            <TextBox />
        </Grid>
    </Grid>
</Window>

Window00.xaml.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.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;

namespace wpf_testproj
{
    /// <summary>
    /// Window00.xaml の相互作用ロジック
    /// </summary>
    public partial class Window00 : Window
    {
        public Window00()
        {
            InitializeComponent();
        }

        private void Window_PreviewKeyDown(object sender, KeyEventArgs e)
        {
            var focused = FocusManager.GetFocusedElement(this) as TextBox;
            if (focused == null) return;

            var grid = focused.Parent as Grid;

            // Ctrl-F2
            if (e.Key == Key.F2 && Keyboard.Modifiers == ModifierKeys.Control)
            {
                var new_grid = this.splitVertical(grid);

                // focus created textbox
                new_grid.Children[0].Focus();
            }
            // Shift-F2
            else if (e.Key == Key.F2 && Keyboard.Modifiers == ModifierKeys.Shift)
            {
                var new_grid = this.splitHorizontal(grid);

                // focus created textbox
                new_grid.Children[0].Focus();
            }
            // Ctrl-F6
            else if (e.Key == Key.F6 && Keyboard.Modifiers == ModifierKeys.Control)
            {
                var sibling = this.destroy(grid);

                // focus textbox in left sibling
                this.find<TextBox>(sibling)?.Focus();
            }
            else
            {
                return;
            }
            e.Handled = true;
        }

        /// <summary>
        /// 横に追加する
        /// </summary>
        /// <param name="grid"></param>
        /// <returns></returns>
        private Grid splitVertical(Grid grid)
        {
            var new_grid = new Grid();

            new_grid.SetValue(Grid.RowProperty, grid.GetValue(Grid.RowProperty));
            new_grid.SetValue(Grid.ColumnProperty, grid.GetValue(Grid.ColumnProperty));

            new_grid.ColumnDefinitions.Add(new ColumnDefinition { MinWidth = 5 });
            new_grid.ColumnDefinitions.Add(new ColumnDefinition { Width = GridLength.Auto });
            new_grid.ColumnDefinitions.Add(new ColumnDefinition { MinWidth = 5 });

            var parent = grid.Parent as Grid;
            parent.Children.Remove(grid);
            parent.Children.Add(new_grid);

            var left = grid;
            left.ClearValue(Grid.RowProperty);
            left.SetValue(Grid.ColumnProperty, 0);
            new_grid.Children.Add(left);

            var right = this.generate();
            right.SetValue(Grid.ColumnProperty, 2);
            new_grid.Children.Add(right);

            var splitter = new GridSplitter
            {
                Width = 1,
                Background = new SolidColorBrush(Colors.Gray),
                HorizontalAlignment = HorizontalAlignment.Stretch,
            };
            splitter.SetValue(Grid.ColumnProperty, 1);
            new_grid.Children.Add(splitter);

            return right;
        }

        /// <summary>
        /// 縦に追加する
        /// </summary>
        /// <param name="grid"></param>
        /// <returns></returns>
        private Grid splitHorizontal(Grid grid)
        {
            var new_grid = new Grid();

            new_grid.SetValue(Grid.RowProperty, grid.GetValue(Grid.RowProperty));
            new_grid.SetValue(Grid.ColumnProperty, grid.GetValue(Grid.ColumnProperty));

            new_grid.RowDefinitions.Add(new RowDefinition { MinHeight = 5 });
            new_grid.RowDefinitions.Add(new RowDefinition { Height = GridLength.Auto });
            new_grid.RowDefinitions.Add(new RowDefinition { MinHeight = 5 });

            var parent = grid.Parent as Grid;
            parent.Children.Remove(grid);
            parent.Children.Add(new_grid);

            var top = grid;
            top.ClearValue(Grid.ColumnProperty);
            top.SetValue(Grid.RowProperty, 0);
            new_grid.Children.Add(top);

            var bottom = this.generate();
            bottom.SetValue(Grid.RowProperty, 2);
            new_grid.Children.Add(bottom);

            var splitter = new GridSplitter
            {
                Height = 1,
                Background = new SolidColorBrush(Colors.Gray),
                HorizontalAlignment = HorizontalAlignment.Stretch
            };
            splitter.SetValue(Grid.RowProperty, 1);
            new_grid.Children.Add(splitter);

            return bottom;
        }

        /// <summary>
        /// 削除
        /// </summary>
        /// <param name="grid"></param>
        /// <returns></returns>
        private Grid destroy(Grid grid)
        {
            var parent = grid.Parent as Grid;
            if (parent == this.root_grid) return null;

            var sibling = (Grid)parent.Children.Cast<UIElement>().First(e => e is Grid && e != grid);
            sibling.SetValue(Grid.RowProperty, parent.GetValue(Grid.RowProperty));
            sibling.SetValue(Grid.ColumnProperty, parent.GetValue(Grid.ColumnProperty));

            var grandparent = parent.Parent as Grid;
            parent.Children.Clear();
            grandparent.Children.Remove(parent);
            grandparent.Children.Add(sibling);

            return sibling;
        }

        private Grid generate()
        {
            return new Grid
            {
                Children = { new TextBox() }
            };
        }

        private T closest<T>(FrameworkElement elem)
            where T : FrameworkElement
        {
            if (elem == null) return null;
            if (elem is T t) return t;
            return this.closest<T>(elem.Parent as FrameworkElement);
        }

        private T find<T>(Grid grid)
            where T : FrameworkElement
        {
            foreach (UIElement i in grid.Children)
            {
                if (i is T t) return t;
                if (i is Grid g)
                {
                    var r = this.find<T>(g);
                    if (r != null) return r;
                }
            }
            return null;
        }
    }
}