WPF TreeView not redrawing

Question

I am new to WPF and I would like TreeView to show expand/collapse icon (the triangle beside node) at all times, regardless whether node has items in it.

To show it at all times, I add a dummy item for nodes that have no items ending up with something like below (for now, I would like to do this in code-behind):

+ Node 1
- Node 2
 - Dummy Item
+ Node 3

Further requirement is to delete Dummy Item once the node having it is expanded.
To do that, I remove the item in OnExpand:

public void OnExpand(object sender, EventArgs e)
{
    ...
    foreach (var item in tvItems){
        if (item is dummy){
            tvItems.Children.Remove(item);
        }
    }
    ...
}

The problem with this is that once node is expanded, I see empty line

+ Node 1
- Node 2
          <-- How to remove this line?
+ Node 3

How do I remove this line so that list shows like:

+ Node 1
  Node 2  // there is no empty line btw Node 2 and Node 3
+ Node 3

vedamsudhakar vedamsudhakar · Accepted Answer · 2016-02-20T05:18:58

try this sample

 <Window x:Class="TreeViewExample.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<Grid>
    <Grid.Resources>
        <HierarchicalDataTemplate x:Key="ChildTemplate" >
            <TextBlock FontStyle="Italic" Text="{Binding Path=Name}" />
        </HierarchicalDataTemplate>
        <HierarchicalDataTemplate x:Key="NameTemplate" ItemsSource="{Binding Path=Books}" 
                                  ItemTemplate="{StaticResource ChildTemplate}" >
            <TextBlock Text="{Binding Path=Name}" FontWeight="Bold" />
        </HierarchicalDataTemplate>
    </Grid.Resources>
    <TreeView HorizontalAlignment="Left" Height="218" VerticalAlignment="Top" Width="175" Margin="76,37,0,0" ItemsSource="{Binding Standards}" ItemTemplate="{StaticResource NameTemplate}" x:Name="tv" TreeViewItem.Expanded="TreeViewItem_Expanded"     />

</Grid>

Here is MainWindow.cs

using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Controls;

namespace TreeViewExample
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
    ObservableCollection<Author> authors = new ObservableCollection<Author>();

    public ObservableCollection<Author> Standards
    {
        get { return authors; }
        set { authors = value; }
    }
    public MainWindow()
    {
        InitializeComponent();
       this.Loaded+=MainWindow_Loaded;
       this.DataContext = this;
    }
    void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        ObservableCollection<Book> Books = new ObservableCollection<Book>();
        Books.Add(new Book() { Id = 1, Name = "X" });
        Books.Add(new Book() { Id = 2, Name = "Y" });
        Books.Add(new Book() { Id = 3, Name = "Z" });

        ObservableCollection<Book> Books2 = new ObservableCollection<Book>();
        Books2.Add(new Book() { Id = 1, Name = "X" });
        Books2.Add(new Book() { Id = 2, Name = "Y" });
        Books2.Add(new Book() { Id = 3, Name = "Z" });


        Standards.Add(new Author() { Name = "I", Books = Books });
        Standards.Add(new Author() { Name = "II" });
        Standards.Add(new Author() { Name = "III", Books = Books2 });
    }

    private void TreeViewItem_Expanded(object sender, RoutedEventArgs e)
    {
        TreeViewItem tvi = e.OriginalSource as TreeViewItem;
        Author author = tvi.Header as Author;
        author.Books.Clear();

    }
}

public class Author
{
    public string Name { get; set; }
    public ObservableCollection<Book> Books { get; set; }
}
public class Book
{
    public int Id { get; set; }
    public string Name { get; set; }
}
}

this example load sample data for the node, whenever you tried to expand the item, sub items will be cleared. let me know is this solve your problem.

WPF TreeView not redrawing

2 Answers