Display Hierarchical Data in TreeView - wpf

Question

I am simply trying to display hierarchical Data in a TreeView, but I just can't figure out how to make it display more than the First two Levels. (And i have read almost evry TreeView post, maybe the problem is my (miss)understatement of the Bindings in this case)
I have simplyfied my Datastructure for this test:
public class Node
{
public List<Node> Children { get; set; }
public Node Parent { get; set; }
public string Expression { get; set; }
}
Xaml currently looks like this: (Please notice that I have changed it several times now, but this here is the original state i have come up with: )
<Window x:Class="Klammern_Test.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Klammern_Test"
Title="MainWindow" Height="439" Width="402">
<Window.Resources>
<HierarchicalDataTemplate DataType="{x:Type local:Node}">
<TreeViewItem ItemsSource="{Binding Children}" Header="{Binding Expression}"/>
</HierarchicalDataTemplate>
</Window.Resources>
<Grid>
<TreeView ItemsSource="{Binding Root}" Margin="12,41,12,12" Name="treeView" />
</Grid>
</Window>
And this is how I am trying to Populate my Treeview:
public partial class MainWindow : Window
{
public Node Root { get; set; }
public MainWindow()
{
InitializeComponent();
DataContext = this;
}
private void StartButton_Click(object sender, RoutedEventArgs e)
{
Parser = new StringParser();
Root = Parser.Parse(Tbx_Eingabe.Text);
treeView.Items.Add(PopulateTreeView(Root));
}
private TreeViewItem PopulateTreeView(Node node)
{
TreeViewItem treeViewItem = new TreeViewItem();
treeViewItem.IsExpanded = true;
treeViewItem.Header = node.Expression;
foreach (Node child in node.Children)
{
treeViewItem.Items.Add(new TreeViewItem() { Header = child.Expression });
if (child.Children.Count > 0)
{
PopulateTreeView(child);
}
}
return treeViewItem;
}
}
What am I missing?
EDIT:
After trying around with almulo's hints, I found this with the Snoop-tool, but I can't tell what it means at all, I have found no other red line and no entry to the Binding Errors column at all.

Answer 1

Using a TreeViewItem inside a HierarchicalDataTemplate which is what your TreeView's TreeViewItems will use to create themselves is... confusing.
Inside your HierarchicalDataTemplate you should just add the controls you want the item "header" to have. In this case, I guess it should be a TextBlock since you just wanna show some text.
Then use the HierarchicalDataTemplate.ItemSource property to bind the children of your node.
<Window.Resources>
<HierarchicalDataTemplate DataType="{x:Type local:Node}"
ItemsSource="{Binding Children}">
<TextBlock Text="{Binding Expression}" />
</HierarchicalDataTemplate>
</Window.Resources>
Also, in you code-behind, you shouldn't manipulate the TreeView.Items or the TreeViewItem.Items directly, since you are already using Bindings and the ItemsSource properties.
Instead, remove the PopulateTreeView method and let your Root property work as items source for the TreeView. But in order for this to work, you'll have to notify the view when the Root property changes its value.
To do so, implement the INotifyPropertyChanged interface and fire the PropertyChanged event every time Root changes.
EDIT: The ItemsControl property ItemsSource expects a collection (more specifically, an IEnumerable), so Root needs to be one. Even if it has a single item, like this:
public class MainWindow : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
// ...
private void StartButton_Click(object sender, RoutedEventArgs e)
{
Parser = new StringParser();
Root = new Node[] { Parser.Parse(Tbx_Eingabe.Text) };
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("Root"));
}
// ...
}