如何在C# WPF中拥有多列下拉框？

using System.Windows;
using System.Windows.Controls;

namespace CustomControls
{
    public class MultiColumnComboBox : ComboBox
    {
        static MultiColumnComboBox()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(MultiColumnComboBox), new FrameworkPropertyMetadata(typeof(MultiColumnComboBox)));
        }

        public static readonly DependencyProperty ItemsSourceProperty =
            DependencyProperty.Register("ItemsSource", typeof(object), typeof(MultiColumnComboBox), new PropertyMetadata(null));

        public object ItemsSource
        {
            get { return GetValue(ItemsSourceProperty); }
            set { SetValue(ItemsSourceProperty, value); }
        }

        public static readonly DependencyProperty SelectedValueProperty =
            DependencyProperty.Register("SelectedValue", typeof(object), typeof(MultiColumnComboBox), new PropertyMetadata(null));

        public object SelectedValue
        {
            get { return GetValue(SelectedValueProperty); }
            set { SetValue(SelectedValueProperty, value); }
        }

        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();

            // 获取下拉框的Popup控件
            var popup = GetTemplateChild("PART_Popup") as Popup;
            if (popup != null)
            {
                // 自定义布局
                var grid = new Grid();
                grid.ColumnDefinitions.Add(new ColumnDefinition());
                grid.ColumnDefinitions.Add(new ColumnDefinition());

                // 第一列展示数据
                var column1ComboBox = new ComboBox();
                column1ComboBox.ItemsSource = ItemsSource;
                column1ComboBox.DisplayMemberPath = "Column1";
                column1ComboBox.SelectedValuePath = "Column1";
                column1ComboBox.SelectionChanged += (sender, e) =>
                {
                    SelectedValue = column1ComboBox.SelectedValue;
                };
                grid.Children.Add(column1ComboBox);

                // 第二列展示数据
                var column2ComboBox = new ComboBox();
                column2ComboBox.ItemsSource = ItemsSource;
                column2ComboBox.DisplayMemberPath = "Column2";
                column2ComboBox.SelectedValuePath = "Column2";
                column2ComboBox.SelectionChanged += (sender, e) =>
                {
                    SelectedValue = column2ComboBox.SelectedValue;
                };
                Grid.SetColumn(column2ComboBox, 1);
                grid.Children.Add(column2ComboBox);

                // 设置Popup的内容为自定义布局
                popup.Child = grid;
            }
        }
    }
}

<Window x:Class="WpfApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:customControls="clr-namespace:CustomControls"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <customControls:MultiColumnComboBox ItemsSource="{Binding Data}" SelectedValue="{Binding SelectedValue}" />
    </Grid>
</Window>