How do I get SelectedItem from a TreeView?

Question

I have a WPF hierarchical TreeView with a TextBlock to show my list. I want to pass the selected string value as a parameter to my ViewModel. I am using MVVM.

Here is the TreeView:

 <TreeView ItemsSource="{Binding countryReportsHierarchy}">
                    <i:Interaction.Triggers>
                        <i:EventTrigger EventName="SelectedItemChanged">
                            <i:InvokeCommandAction Command="{Binding ArticleCategoryTitleSelectionChangedCommand}" />
                        </i:EventTrigger>
                    </i:Interaction.Triggers>
                    <TreeView.Resources>
                        <HierarchicalDataTemplate  DataType="{x:Type t:CountryReportsHierarchy}"
                                ItemsSource="{Binding ArticleCategoriesHierarchyCollection}">
                            <TextBlock Text="{Binding Name}" />
                        </HierarchicalDataTemplate>
                        <HierarchicalDataTemplate  DataType="{x:Type t:ArticleCategoriesHierarchy}"
                                ItemsSource="{Binding ArticleTypesHierarchyCollection}">
                            <TextBlock Text="{Binding Name}"/>
                        </HierarchicalDataTemplate>
                        <DataTemplate  DataType="{x:Type t:ArticleTypesHierarchy}">
                            <TextBlock Text="{Binding ElementName= Name, Path=SelectedItem, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" >
                            </TextBlock>
                        </DataTemplate>
                    </TreeView.Resources>
                </TreeView>

And the part I am trying to get selected value from the TextBlock from:

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

This binds as expected, obviously without selected value. Is there any way to pass the selected value of a TextBlock? I've tried the following but the binding fails:

<TextBlock Text="{Binding ElementName= Name, Path=SelectedItem" />

Answer 1

Here's how I solved this. I extended the TreeView class to include SelectedItem functionality:

public class ExtendedTreeView : TreeView
{
    public ExtendedTreeView()
        : base()
    {
        this.SelectedItemChanged += new RoutedPropertyChangedEventHandler<object>(___ICH);
    }

    void ___ICH(object sender, RoutedPropertyChangedEventArgs<object> e)
    {
        if (SelectedItem != null)
        {
            SetValue(SelectedItem_Property, SelectedItem);
        }
    }

    public object SelectedItem_
    {
        get { return (object)GetValue(SelectedItem_Property); }
        set { SetValue(SelectedItem_Property, value); }
    }
    public static readonly DependencyProperty SelectedItem_Property = DependencyProperty.Register("SelectedItem_", typeof(object), typeof(ExtendedTreeView), new UIPropertyMetadata(null));
}

Here are my hierarchy classes for the TreeView:

   public class CountryReportsHierarchy
{
    IIsesServiceChannel IsesService;
    public ObservableCollection<tbArticleCategory> ArticleCategoryList;

    public ObservableCollection<ArticleCategoriesHierarchy> ArticleCategoriesHierarchyCollection { get; set; }
    public string Name { get; set; }

    public CountryReportsHierarchy(IIsesServiceChannel isesService)
    {
        this.IsesService = isesService;          
        ArticleCategoryList = new ObservableCollection<tbArticleCategory>(IsesService.GetArticleCatagoryTitles());           

        ArticleCategoriesHierarchyCollection = new ObservableCollection<ArticleCategoriesHierarchy>();

        foreach (var a in ArticleCategoryList)
        {
            ArticleCategoriesHierarchyCollection.Add(new ArticleCategoriesHierarchy(IsesService, a.Category) { Name = a.CategoryTitle });
        }
    } 
}

public class ArticleCategoriesHierarchy
{
    IIsesServiceChannel IsesService;

    public ObservableCollection<tbArticleType> ArticleTypeList;
    public ObservableCollection<ArticleTypesHierarchy> ArticleTypesHierarchyCollection { get; set; }
    public string Name { get; set; }
    public ArticleCategoriesHierarchy(IIsesServiceChannel isesService, string articleCategoryType)
    {
        this.IsesService = isesService;

        ArticleTypeList = new ObservableCollection<tbArticleType>(IsesService.GetArticleCategoryTypes(articleCategoryType));

        ArticleTypesHierarchyCollection = new ObservableCollection<ArticleTypesHierarchy>();

        foreach (var a in ArticleTypeList)
        {
            ArticleTypesHierarchyCollection.Add(new ArticleTypesHierarchy() { Name = a.ArticleTitle });
        }
    }
}

public class ArticleTypesHierarchy
{
    public string Name { get; set; }
}

I then bound my new ExtendedTreeView Selected item to a ArticleTypesHierarchy property in my ViewModel:

 <cntrls:ExtendedTreeView ItemsSource="{Binding countryReportsHierarchy}" SelectedItem_="{Binding SelectedArticleTitle, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" >                       
                    <i:Interaction.Triggers>
                        <i:EventTrigger EventName="SelectedItemChanged">
                            <i:InvokeCommandAction Command="{Binding ArticleCategoryTitleSelectionChangedCommand}" />
                        </i:EventTrigger>
                    </i:Interaction.Triggers>
                    <TreeView.Resources>
                        <HierarchicalDataTemplate  DataType="{x:Type t:CountryReportsHierarchy}"
                                ItemsSource="{Binding ArticleCategoriesHierarchyCollection}">
                            <TextBlock Text="{Binding Name}" />
                        </HierarchicalDataTemplate>
                        <HierarchicalDataTemplate  DataType="{x:Type t:ArticleCategoriesHierarchy}"
                                ItemsSource="{Binding ArticleTypesHierarchyCollection}">
                            <TextBlock Text="{Binding Name}"/>
                        </HierarchicalDataTemplate>
                        <DataTemplate  DataType="{x:Type t:ArticleTypesHierarchy}">                              
                            <TextBlock Text="{Binding Name}" />                  
                        </DataTemplate>
                    </TreeView.Resources>
                </cntrls:ExtendedTreeView>

ViewModel passing in the ArticleTypesHierarchy.Name (My selected TreeView string) argument:

    public ReportViewModel()
    {
        countryReportsHierarchy = new ObservableCollection<CountryReportsHierarchy>(new[]{
        new CountryReportsHierarchy(IsesService){Name = CountryReportTitle}});
    }


  private ArticleTypesHierarchy _SelectedArticleTitle;
    public ArticleTypesHierarchy SelectedArticleTitle
    {
        get { return _SelectedArticleTitle; }
        set
        {
            _SelectedArticleTitle = value;
            OnPropertyChanged("SelectedArticleTitle");
        }
    }      

    private void ArticleCategoryTitleSelectionChangedCommandAction()
    {
        GetData(SelectedArticleTitle.Name)
    }