WIn_RustTools/RustTools/Editor/EditorWin.xaml

<?xml version="1.0" encoding="utf-8" ?>
<windowex:WindowEx
    x:Class="RustTools.Editor.EditorWin"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:controlpages="using:RustTools.Editor"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="using:RustTools"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:windowex="using:WinUIEx"
    MinWidth="500"
    MinHeight="500"
    mc:Ignorable="d">

    <Page Name="page">
        <Page.Resources>
            <DataTemplate x:Key="FolderTemplate">
                <TreeViewItem
                    AutomationProperties.Name="{Binding Name}"
                    IsExpanded="False"
                    ItemsSource="{Binding Children}">
                    <StackPanel Orientation="Horizontal">
                        <FontIcon Glyph="&#xE8B7;" />
                        <TextBlock Margin="0,0,10,0" />
                        <TextBlock Text="{Binding Name}" />
                    </StackPanel>
                </TreeViewItem>
            </DataTemplate>

            <DataTemplate x:Key="FileTemplate">
                <TreeViewItem AutomationProperties.Name="{Binding Name}">
                    <StackPanel Orientation="Horizontal">
                        <FontIcon Glyph="&#xE8A5;" />
                        <TextBlock Margin="0,0,10,0" />
                        <TextBlock Text="{Binding Name}" />
                    </StackPanel>
                </TreeViewItem>
            </DataTemplate>
            <controlpages:ExplorerItemTemplateSelector
                x:Key="ExplorerItemTemplateSelector"
                FileTemplate="{StaticResource FileTemplate}"
                FolderTemplate="{StaticResource FolderTemplate}" />

            <TabViewItem x:Key="FileTab">
                <TextBox
                    x:Name="MyTextBox"
                    Height="200"
                    AcceptsReturn="True"
                    TextWrapping="Wrap" />
            </TabViewItem>
        </Page.Resources>

        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto" />
                <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto" />
                <RowDefinition Height="*" />
            </Grid.RowDefinitions>
            <Grid
                Grid.Row="0"
                Padding="9"
                Visibility="Visible">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="Auto" />
                    <ColumnDefinition />
                    <ColumnDefinition Width="Auto" />
                </Grid.ColumnDefinitions>
                <TextBlock
                    Name="TitleText"
                    Grid.Column="0"
                    Margin="16,0,0,0" />
            </Grid>

            <ScrollViewer
                Grid.Row="2"
                Grid.Column="0"
                Width="300"
                Margin="0,9,0,6"
                Padding="0,0,16,0"
                HorizontalScrollBarVisibility="Visible"
                HorizontalScrollMode="Auto"
                IsHorizontalRailEnabled="True"
                IsHorizontalScrollChainingEnabled="True">

                <TreeView
                    Name="treeView"
                    Grid.Row="2"
                    Grid.Column="0"
                    ItemInvoked="TreeView_ItemInvoked"
                    ItemTemplateSelector="{StaticResource ExplorerItemTemplateSelector}"
                    ItemsSource="{x:Bind DataSource}"
                    KeyDown="treeView_KeyDown"
                    KeyUp="treeView_KeyUp"
                    SelectionMode="Single" />
            </ScrollViewer>

            <ScrollViewer
                Grid.Row="1"
                Grid.Column="1"
                HorizontalScrollBarVisibility="Visible"
                HorizontalScrollMode="Auto"
                IsHorizontalRailEnabled="True"
                IsHorizontalScrollChainingEnabled="True">

                <Grid
                    x:Name="gridedit"
                    Grid.Row="1"
                    Grid.Column="1">

                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto" />
                        <ColumnDefinition />
                    </Grid.ColumnDefinitions>

                    <ListBox
                        Grid.Column="0"
                        Margin="0,0,10,0"
                        Background="Transparent"
                        ItemsSource="{x:Bind lineNumberList}"
                        ScrollViewer.IsVerticalRailEnabled="False">
                        <ListBox.ItemContainerStyle>
                            <Style TargetType="ListBoxItem">
                                <Setter Property="Padding" Value="0" />
                            </Style>
                        </ListBox.ItemContainerStyle>
                        <ListBox.ItemTemplate>
                            <DataTemplate>
                                <TextBlock Name="listboxtext" Text="{Binding}" />
                            </DataTemplate>
                        </ListBox.ItemTemplate>
                    </ListBox>
                    <RichEditBox
                        x:Name="editor"
                        Grid.Column="1"
                        Background="Transparent"
                        TextChanged="editor_TextChanged" />
                </Grid>
            </ScrollViewer>
        </Grid>
    </Page>
</windowex:WindowEx>