mvvm treeview不绑定视图模型

Question

我在树视图的执行中缺少什么？ 这是什么东西看：

查看：

<TreeView Style="{StaticResource ExpandAllStyle}" ItemsSource="{Binding Titles}"> 
      <TreeView.Resources> 
       <HierarchicalDataTemplate DataType="{x:Type vm:TitleViewModel}"> 
        <Grid ShowGridLines="False"> 
         <Grid.ColumnDefinitions> 
          <ColumnDefinition /> 
          <ColumnDefinition /> 
          <ColumnDefinition /> 
         </Grid.ColumnDefinitions> 

         <TextBlock Text="{Binding Path=DisplayedStartTime}" Margin="0,0,10,0" /> 
         <TextBlock Grid.Column="1" Text="" /> 
         <TextBlock Grid.Column="2" Text="{Binding Path=Text}" /> 
        </Grid> 
       </HierarchicalDataTemplate> 
      </TreeView.Resources> 
     </TreeView> 

我的仓库：

public class TitleRepository : INotifyPropertyChanged 
{ 
    #region Titles 

    private ObservableCollectionEx<Title> _titles; 

    public ObservableCollectionEx<Title> Titles 
    { 
     get { return _titles; } 
     set 
     { 
      _titles = value; 
      OnPropertyChanged(new PropertyChangedEventArgs("Titles")); 
     } 
    } 

    #endregion 

    #region Current Title 

    private Title _currentTitle; 

    public Title CurrentTitle 
    { 
     get { return _currentTitle; } 
     set { _currentTitle = value; } 
    } 

    #endregion 

    public TitleRepository() 
    { 
     _titles = new ObservableCollectionEx<Title>(); 

     _titles.Add(new Title("This is a title test")); 
    } 

和我的视图模型： MainTreeViewModel：

public class MainTreeViewModel : ViewModelBase 
    { 
     private readonly TitleRepository _titleRepository; 

     private ObservableCollection<TitleViewModel> _titles; 

     public ObservableCollection<TitleViewModel> Titles 
     { 
      get { return _titles; } 
      set { _titles = value; } 
     } 

     public MainTreeViewModel() 
     { 
      _titleRepository = ((App)Application.Current).TitleRepository; 

      _titleRepository.Titles.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(Titles_CollectionChanged); 

      _titles = new ObservableCollection<TitleViewModel>(
       (from t in _titleRepository.Titles 
       select new TitleViewModel(t)).ToList()); 
     } 

     void Titles_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) 
     { 
      _titles.Add(new TitleViewModel(_titleRepository.Titles[_titleRepository.Titles.Count - 1])); 
     } 

TitleViewModel：

public class TitleViewModel : ViewModelBase 
    { 
     readonly Title _title; 

     #region Displayed Start Time 

     public string DisplayedStartTime 
     { 
      get { return _title.DisplayedStartTime; } 
     } 

     #endregion 

     #region Text 

     public string Text 
     { 
      get { return _title.Text; } 
     } 

     #endregion 

     public TitleViewModel(Title title) 
     { 
      _title = title; 


     } 

我视图模型绑定在View.cs：

 MainTreeViewModel vm = new MainTreeViewModel(); 
     this.DataContext = vm; 

我希望看到的标题是“这是一个砖试验”，我在仓库中填充。 它是一个动态树。