回答編集履歴

  過去の回答の使いまわしなので、例としてはちょっと重めですが

  <!-- 直置きパターン -->

  <local:TreeUserControl DataContext="{Binding Tree}" />

  <!-- DataTemplateパターン -->

  <ContentPresenter Grid.Column="1" Content="{Binding Tree}" />

  ```

  この２つの違いと、（結果的には何も変わらないのですが^^; 初めて見たときは「はぁ～なるほど！」と思いました）

  `TreeViewModel`・`TreeUserControl`の関係を見てください。

 

  `TreeUserControl`が`TreeView`だけなのは、ちょっともったいない？かもしれません。

  ボタン類も一緒に入れると、責務がきれいに分かれたようになると思います。

 

  `MainViewModel`が`TreeViewModel`を保持しているので、`MainViewModel`からツリーの状態はいつでも見れます。

 

  `DependencyProperty`は特に出番はありませんでした。

  左右は同じ`TreeViewModel`を見ているので、自動的に連動します。

  これでは意味がないですが、チェックされてるものだけ表示する（`TreeView`だと大変すぎるが^^; `ListBox`なんかは簡単）等、差をつけるときに`DependencyProperty`があれば便利です。

 

  <Window

  x:Class="Questions292544.MainWindow"

  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  xmlns:local="clr-namespace:Questions292544"

  Width="800"

  Height="450">

  <Window.DataContext>

  <local:MainViewModel />

  </Window.DataContext>

  <Window.Resources>

  <DataTemplate DataType="{x:Type local:TreeViewModel}">

  <local:TreeUserControl />

  </DataTemplate>

  <Style TargetType="Button">

  <Setter Property="Margin" Value="5" />

  </Style>

  </Window.Resources>

  <DockPanel>

  <StackPanel DockPanel.Dock="Top" Orientation="Horizontal">

  <Button Command="{Binding Tree.AllCheckCmd}" Content="全チェック" />

  <Button Command="{Binding Tree.AllUncheckCmd}" Content="全アンチェック" />

  <Button Command="{Binding Tree.AllExpandCmd}" Content="全展開" />

  <Button Command="{Binding Tree.AllContractCmd}" Content="全畳む" />

  <Button Command="{Binding Tree.AddNodeCmd}" Content="ノード追加" />

  <Button Command="{Binding PrintCheckedNodesCmd}" Content="チェックノード表示（Debug）" />

  </StackPanel>

  <Grid>

  <Grid.ColumnDefinitions>

  <ColumnDefinition />

  <ColumnDefinition />

  </Grid.ColumnDefinitions>

  <!-- 直置きパターン -->

  <local:TreeUserControl DataContext="{Binding Tree}" />

  <!-- DataTemplateパターン -->

  <ContentPresenter Grid.Column="1" Content="{Binding Tree}" />

  </Grid>

  </DockPanel>

  </Window>

  ```

 

  <UserControl

  x:Class="Questions292544.TreeUserControl"

  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"

  d:DesignHeight="450"

  d:DesignWidth="800"

  mc:Ignorable="d">

  <TreeView ItemsSource="{Binding Root.Children}">

  <TreeView.ItemTemplate>

  <HierarchicalDataTemplate ItemsSource="{Binding Children}">

  <StackPanel Orientation="Horizontal">

  <CheckBox

  Margin="5"

  VerticalContentAlignment="Center"

  IsChecked="{Binding IsChecked}" />

  <TextBlock Margin="5" Text="{Binding Name}" />

  <Button

  Margin="5"

  Command="{Binding DataContext.DeleteNodeCmd, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type TreeView}}}"

  CommandParameter="{Binding}"

  Content="削除" />

  </StackPanel>

  </HierarchicalDataTemplate>

  </TreeView.ItemTemplate>

  <TreeView.ItemContainerStyle>

  <Style TargetType="{x:Type TreeViewItem}">

  <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />

  <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />

  </Style>

  </TreeView.ItemContainerStyle>

  </TreeView>

  </UserControl>

  ```

 

  他コード

  using System;

  using System.Collections;

  using System.Collections.Generic;

  using System.Collections.ObjectModel;

  using System.ComponentModel;

  using System.Diagnostics;

  using System.Linq;

  using System.Runtime.CompilerServices;

  using System.Windows.Input;

 

  namespace Questions292544

  {

  class MainViewModel : Observable

  public TreeViewModel Tree { get; } = new TreeViewModel();

  public RelayCommand PrintCheckedNodesCmd { get; }

  public MainViewModel()

  PrintCheckedNodesCmd = new RelayCommand(() =>

  {

  Debug.WriteLine("IsChecked"); // チェックを入れた最上位の情報表示

 

  foreach(var c in Tree.Root.Children) Dfs(c);

 

  void Dfs(TreeNode node) // 深さ優先探索

  {

  if(node.IsChecked == true)

  {

  Debug.WriteLine(node.Name);

  return;

  }

  foreach(var c in node.Children) Dfs(c);

  }

  });

 

  class TreeViewModel : Observable

  public TreeNode Root { get; }

 

  public RelayCommand AllCheckCmd { get; }

  public RelayCommand AllUncheckCmd { get; }

  public RelayCommand AllExpandCmd { get; }

  public RelayCommand AllContractCmd { get; }

  public RelayCommand<TreeNode> DeleteNodeCmd { get; }

  public RelayCommand AddNodeCmd { get; }

 

  public TreeViewModel()

  Root = new TreeNode("Root") {

  new TreeNode("Node1") {

  new TreeNode("Node1-1"),

  new TreeNode("Node1-2") {

  new TreeNode("Node1-2-1"),

  new TreeNode("Node1-2-2"),

  },

  },

  new TreeNode("Node2") {

  new TreeNode("Node2-1") {

  new TreeNode("Node2-1-1"),

  new TreeNode("Node2-1-2"),

  },

  },

  };

 

  AllCheckCmd = new RelayCommand(() => { foreach(var c in Root) c.IsChecked = true; });

  AllUncheckCmd = new RelayCommand(() => { foreach(var c in Root) c.IsChecked = false; });

  AllExpandCmd = new RelayCommand(() => { foreach(var c in Root) c.IsExpanded = true; });

  AllContractCmd = new RelayCommand(() => { foreach(var c in Root) c.IsExpanded = false; });

  DeleteNodeCmd = new RelayCommand<TreeNode>((c) => c.Parent.Remove(c));

  AddNodeCmd = new RelayCommand(() =>

  {

  // 選択の子に追加

  if(Root.FirstOrDefault(x => x.IsSelected) is TreeNode selectedItem)

  selectedItem.Add(new TreeNode("NewNode"));

  else Root.Add(new TreeNode("NewNode"));

  });

 

  class TreeNode : Observable, IEnumerable<TreeNode>

  string _Name;

  public string Name { get => _Name; set => Set(ref _Name, value); }

 

  bool _IsExpanded;

  public bool IsExpanded { get => _IsExpanded; set => Set(ref _IsExpanded, value); }

 

  bool _IsSelected;

  public bool IsSelected { get => _IsSelected; set => Set(ref _IsSelected, value); }

 

  bool? _IsChecked = false;

  public bool? IsChecked // ThreeState

  get => _IsChecked;

  set

  {

  if(_IsChecked == value) return;

  if(reentrancyCheck) return; // 再入防止

  reentrancyCheck = true;

  Set(ref _IsChecked, value);

  UpdateCheckState(); // チェックが変わったら上下も更新

  reentrancyCheck = false;

  }

 

  public ObservableCollection<TreeNode> Children { get; } = new ObservableCollection<TreeNode>();

 

  public TreeNode Parent { get; private set; } // 追加・削除の簡便さのため親ノードが欲しい

 

  bool reentrancyCheck;

 

  public TreeNode(string name) => Name = name;

 

  public void Add(TreeNode child)

  child.Parent = this;

  Children.Add(child);

  IsExpanded = true;

  child.UpdateCheckState();

  public void Remove(TreeNode child)

  Children.Remove(child);

  child.Parent = null;

  if(0 < Children.Count) IsChecked = DetermineCheckState();

 

  //チェック状態反映

  // https://docs.telerik.com/devtools/wpf/controls/radtreeview/how-to/howto-tri-state-mvvm

  void UpdateCheckState()

  if(0 < Children.Count) UpdateChildrenCheckState();

  if(Parent != null) Parent.IsChecked = Parent.DetermineCheckState();

  void UpdateChildrenCheckState()

  foreach(var c in Children)

  {

  if(IsChecked != null) c.IsChecked = IsChecked;

  }

  bool? DetermineCheckState()

  var checkCount = Children.Count(x => x.IsChecked == true);

  if(checkCount == Children.Count) return true;

 

  var uncheckCount = Children.Count(x => x.IsChecked == false);

  if(uncheckCount == Children.Count) return false;

 

  return null;

 

  // 子孫を全列挙（Children列挙でないので注意）

  IEnumerable<TreeNode> Descendants(TreeNode node) => node.Children.Concat(node.Children.SelectMany(Descendants));

  public IEnumerator<TreeNode> GetEnumerator() => Descendants(this).GetEnumerator();

  IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

 

  class Observable : INotifyPropertyChanged

  public event PropertyChangedEventHandler PropertyChanged;

  protected void Set<T>(ref T storage, T value, [CallerMemberName] string name = null)

  if(Equals(storage, value)) return;

  storage = value;

  OnPropertyChanged(name);

  protected void OnPropertyChanged(string name) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));

  class RelayCommand : ICommand

  readonly Action exec;

  readonly Func<bool> can;

  public event EventHandler CanExecuteChanged;

  public RelayCommand(Action e) : this(e, null) { }

  public RelayCommand(Action e, Func<bool> c)

  exec = e ?? throw new ArgumentNullException(nameof(e));

  can = c;

  public bool CanExecute(object _) => can == null || can();

  public void Execute(object _) => exec();

  public void OnCanExecuteChanged() => CanExecuteChanged?.Invoke(this, EventArgs.Empty);

  class RelayCommand<T> : ICommand

  readonly Action<T> exec;

  readonly Func<T, bool> can;

  public event EventHandler CanExecuteChanged;

  public RelayCommand(Action<T> e) : this(e, null) { }

  public RelayCommand(Action<T> e, Func<T, bool> c)

  exec = e ?? throw new ArgumentNullException(nameof(e));

  can = c;

  public bool CanExecute(object p) => can == null || can((T)p);

  public void Execute(object p) => exec((T)p);

  public void OnCanExecuteChanged() => CanExecuteChanged?.Invoke(this, EventArgs.Empty);

  }

  ```

  .xaml.csは初期状態

 

  ---

 

  `TreeNode`は厳密には`ViewModel`になるかもしれませんが、ライブラリなしではめんどくさいのでVM・M兼用です^^;