WPF TreeView数据绑定代码仅显示一级数据，请求修正

问题背景 #

我是C#与WPF的初学者，在研究TreeView数据绑定方法时，参考了HierarchicalDataTemplate相关示例，自行编写了实体类及XAML代码，但运行后TreeView仅能展示第一级数据。以下是我的原始代码：

原始实体类：ListLeagueList #

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections.ObjectModel;

namespace Treeview01
{
    public class ListLeagueList : ObservableCollection<League>
    {
        public ListLeagueList() : base()
        {
            Add(new League("League A"));
            Add(new League("League B"));
            Add(new League("League C"));
        }
    }
}

原始实体类：League #

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections.ObjectModel;

namespace Treeview01
{
    public class League
    {
        public string Name { get; set; }

        List<Division> Divisions  = new List<Division>();
        public League(string name)
        {
            Name = name;
            Divisions.Add(new Division("DivisionA"));
            Divisions.Add(new Division("DivisionB"));
            Divisions.Add(new Division("DivisionC"));
        }
        private League()
        {
        }
    }
}

原始实体类：Division #

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections.ObjectModel;

namespace Treeview01
{
    public class Division
    {
        public string Name { get; set; }

        List<Team> Teams = new List<Team>();
        public Division(string name)
        {
            Name = name;
            Teams.Add(new Team("Bear"));
            Teams.Add(new Team("Rocket"));
        }
        private Division()
        {
        }

    }
}

原始实体类：Team #

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Treeview01
{
    public class Team
    {
        public string Name { get; set; }

        public Team(string name)
        {
            Name = name;
        }

        private Team()
        {
        }
    }
}

原始XAML代码 #

<Window x:Class="Treeview01.Window1"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      Title="HierarchicalDataTemplate Sample"
      xmlns:src="clr-namespace:Treeview01">
        <DockPanel>
            <DockPanel.Resources>
                <src:ListLeagueList x:Key="MyList"/>

                <HierarchicalDataTemplate DataType    = "{x:Type src:League}"
                                    ItemsSource = "{Binding Path=Divisions}">
                    <TextBlock Text="{Binding Path=Name}"/>
                </HierarchicalDataTemplate>

                <HierarchicalDataTemplate DataType    = "{x:Type src:Division}"
                                    ItemsSource = "{Binding Path=Teams}">
                    <TextBlock Text="{Binding Path=Name}"/>
                </HierarchicalDataTemplate>

                <DataTemplate DataType="{x:Type src:Team}">
                    <TextBlock Text="{Binding Path=Name}"/>
                </DataTemplate>
                
            </DockPanel.Resources>

            <Menu Name="menu1" DockPanel.Dock="Top" Margin="10,10,10,10">
                <MenuItem Header="My Soccer Leagues"
                      ItemsSource="{Binding Source={StaticResource MyList}}" />
            </Menu>

            <TreeView>
                <TreeViewItem ItemsSource="{Binding Source={StaticResource MyList}}" Header="My Soccer Leagues" />
            </TreeView>

        </DockPanel>
    </Window>

原始XAML.CS代码 #

using System.Windows;

namespace Treeview01
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

    }
}

运行后仅显示第一级数据：

问题原因 #

核心问题是实体类中的子集合（Divisions、Teams）为私有字段，WPF数据绑定机制只能访问公共属性，无法识别私有字段，因此子级数据无法被HierarchicalDataTemplate加载展示。

修正方案 #

将实体类中的私有子集合字段改为公共的只读属性，推荐使用ObservableCollection<T>替代List<T>（支持集合变更通知，后续修改集合时UI能自动更新）。

修正后的League类 #

using System;
using System.Collections.ObjectModel;

namespace Treeview01
{
    public class League
    {
        public string Name { get; set; }
        // 改为公共只读ObservableCollection属性
        public ObservableCollection<Division> Divisions { get; } = new ObservableCollection<Division>();

        public League(string name)
        {
            Name = name;
            Divisions.Add(new Division("DivisionA"));
            Divisions.Add(new Division("DivisionB"));
            Divisions.Add(new Division("DivisionC"));
        }
        private League()
        {
        }
    }
}

修正后的Division类 #

using System;
using System.Collections.ObjectModel;

namespace Treeview01
{
    public class Division
    {
        public string Name { get; set; }
        // 改为公共只读ObservableCollection属性
        public ObservableCollection<Team> Teams { get; } = new ObservableCollection<Team>();

        public Division(string name)
        {
            Name = name;
            Teams.Add(new Team("Bear"));
            Teams.Add(new Team("Rocket"));
        }
        private Division()
        {
        }
    }
}

其他代码保持不变 #

ListLeagueList、Team类及XAML、XAML.CS代码无需修改。

效果验证 #

修改后运行程序，TreeView将正常展示所有层级的数据（联赛→分区→球队），Menu控件也会同步显示完整层级。

内容的提问来源于stack exchange，提问作者Colin