CompositeCollection の使い方が分からない・・・

XAML 上で CompositeCollection を挟むと表示されないんです。使い方は合っているような気がするのですが、なんでや～。 XAML 上だと CompositeCollection がプロパティメンバーではなくなるとか？分からない...

表示されない

<Window x:Class="WpfApp14.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:WpfApp14"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    
    <ListBox>
        <ListBox.ItemsSource>
            <CompositeCollection>
                <CollectionContainer Collection="{Binding Items1}" />
                <CollectionContainer Collection="{Binding Items2}" />
                <CollectionContainer Collection="{Binding Items3}" />
            </CompositeCollection>
        </ListBox.ItemsSource>
    </ListBox>
    
</Window>

using System.Collections.Generic;
using System.Windows;

namespace WpfApp14
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        public List<string> Items1 { get; set; }
        public List<string> Items2 { get; set; }
        public List<int> Items3 { get; set; }

        public MainWindow()
        {
            InitializeComponent();

            DataContext = this;

            Items1 = new List<string> { "aaa", "bbb", "ccc" };
            Items2 = new List<string> { "ddd", "eee", "fff" };
            Items3 = new List<int> { 1, 2, 3 };

        }
    }
}

表示される

<Window x:Class="WpfApp14.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:WpfApp14"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">

    <ListBox ItemsSource="{Binding Items}" />

</Window>

using System.Collections.Generic;
using System.Windows;
using System.Windows.Data;

namespace WpfApp14
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        public CompositeCollection Items { get; set; }

        public MainWindow()
        {
            InitializeComponent();

            DataContext = this;

            var Items1 = new List<string> { "aaa", "bbb", "ccc" };
            var Items2 = new List<string> { "ddd", "eee", "fff" };
            var Items3 = new List<int> { 1, 2, 3 };

            Items = new CompositeCollection();
            Items.Add(new CollectionContainer() { Collection = Items1 });
            Items.Add(new CollectionContainer() { Collection = Items2 });
            Items.Add(new CollectionContainer() { Collection = Items3 });

        }
    }
}

追記

リソース経由で CollectionViewSource 経由で参照することで表示できるようになったよ！わーい！ってなるかーぼけー！という感想を持ちました。遠回り過ぎるですよ。

<Window x:Class="WpfApp14.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:WpfApp14"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">

    <Window.Resources>
        <CollectionViewSource x:Key="Items1Source" Source="{Binding Items1}" />
        <CollectionViewSource x:Key="Items2Source" Source="{Binding Items2}" />
        <CollectionViewSource x:Key="Items3Source" Source="{Binding Items3}" />
    </Window.Resources>

    <ListBox>
        <ListBox.ItemsSource>
            <CompositeCollection>
                <CollectionContainer Collection="{Binding Source={StaticResource Items1Source}}" />
                <CollectionContainer Collection="{Binding Source={StaticResource Items2Source}}" />
                <CollectionContainer Collection="{Binding Source={StaticResource Items3Source}}" />
            </CompositeCollection>
        </ListBox.ItemsSource>
    </ListBox>

</Window>

using System.Collections.Generic;
using System.Windows;

namespace WpfApp14
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        public List<string> Items1 { get; set; }
        public List<string> Items2 { get; set; }
        public List<int> Items3 { get; set; }

        public MainWindow()
        {
            InitializeComponent();

            DataContext = this;

            Items1 = new List<string> { "aaa", "bbb", "ccc" };
            Items2 = new List<string> { "ddd", "eee", "fff" };
            Items3 = new List<int> { 1, 2, 3 };

        }
    }
}