Repeated children in WPF TreeView - wpf

Question

Solved it myself. It was the way I initialised the Settings collection. Specifying a default when registering it as a DependencyProperty causes all of the Settings to refer to the same collection object. Adding a constructor to Category and explicitly initialising Settings resolves the issue.
A class Category specifies a name and a collection of Settings objects.
using System.Collections.ObjectModel;
using System.Windows;
namespace CasEdit
{
public class Categories : ObservableCollection<Category> { }
public class Category : DependencyObject
{
public string Caption
{
get { return (string)GetValue(CategoryProperty); }
set { SetValue(CategoryProperty, value); }
}
public static readonly DependencyProperty CategoryProperty =
DependencyProperty.Register("Caption", typeof(string), typeof(Category),
new UIPropertyMetadata("Category name not set"));
public Settings Settings
{
get { return (Settings)GetValue(SettingsProperty); }
}
public static readonly DependencyProperty SettingsProperty =
DependencyProperty.Register("Settings", typeof(Settings), typeof(Category),
new UIPropertyMetadata(new Settings()));
}
}
The following XAML defines templates, UI and some test data.
<Window x:Class="CasEdit.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:CasEdit="clr-namespace:CasEdit"
Title="MainWindow" Height="350" Width="525" >
<Window.Resources>
<HierarchicalDataTemplate DataType="{x:Type CasEdit:Category}" ItemsSource="{Binding Settings}">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Caption}" />
<Button Content="Gratuitous button" Margin="3" Click="Button_Click"/>
</StackPanel>
</HierarchicalDataTemplate>
<DataTemplate DataType="{x:Type CasEdit:Setting}" >
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Caption}" Margin="3" />
<TextBlock Text="{Binding Template}" Margin="3" />
<TextBox Text="{Binding Editor}" Margin="3" />
<TextBlock Text="{Binding CasDevice}" Margin="3" />
</StackPanel>
</DataTemplate>
<CasEdit:Categories x:Key="cats">
<CasEdit:Category Caption="1st category">
<CasEdit:Category.Settings>
<CasEdit:Setting Caption="Setting 1-1" />
<CasEdit:Setting Caption="Setting 1-2" />
</CasEdit:Category.Settings>
</CasEdit:Category>
<CasEdit:Category Caption="2nd category" >
<CasEdit:Category.Settings>
<CasEdit:Setting Caption="Setting 2-1" />
</CasEdit:Category.Settings>
</CasEdit:Category>
<CasEdit:Category Caption="3rd category" >
<CasEdit:Category.Settings>
<CasEdit:Setting Caption="Setting 3-1" />
</CasEdit:Category.Settings>
</CasEdit:Category>
</CasEdit:Categories>
</Window.Resources>
<Grid>
<TreeView x:Name="tree" ItemsSource="{Binding Source={StaticResource cats}}" />
</Grid>
</Window>
You would expect a tree like this
1st category
Setting 1-1
Setting 1-2
2nd Category
Setting 2-1
3rd category
Setting 3-1
but what I get is this
which is very confusing. Where have I gone astray, that each category shows all of the settings?

Answer 1

The last parameter here is telling making it so that every instance of Category has it's Settings property initialized to point to the same object:
public static readonly DependencyProperty SettingsProperty =
DependencyProperty.Register("Settings", typeof(Settings), typeof(Category),
new UIPropertyMetadata(new Settings()));
Instead, do this:
public static readonly DependencyProperty SettingsProperty =
DependencyProperty.Register("Settings", typeof(Settings), typeof(Category),
new UIPropertyMetadata(null));
public Category()
{
Settings = new Settings();
}