Code

<Style TargetType="{x:Type local:MyContainerNode}">
	<Setter Property="Template">
		<Setter.Value>
			<DataTemplate DataType="{x:Type local:MyContainerNode}">
				<Border
					BorderBrush="{Binding Stroke}"
					BorderThickness="1"
					Background="{Binding Brush}">
					<Grid>
						<Grid.RowDefinitions>
							<RowDefinition Height="Auto" />
							<RowDefinition Height="*" />
						</Grid.RowDefinitions>
						<TextBlock Height="{Binding CaptionHeight}" Text="{Binding Text}" />
					</Grid>
				</Border>
			</DataTemplate>
		</Setter.Value>
	</Setter>
</Style>

class MyContainerNode : ContainerNode
{
	static MyContainerNode()
	{
		DefaultStyleKeyProperty.OverrideMetadata(
			typeof(MyContainerNode),
			new FrameworkPropertyMetadata(typeof(MyContainerNode)));
	}
	/// <summary>
	/// Initializes a new instance of the MyContainerNode class.
	/// </summary>
	public MyContainerNode(Diagram parent)
		: base(parent)
	{
		EnsureTemplate();
	}

	public override void Draw(DrawingContext graphics,
		MindFusion.Diagramming.Wpf.RenderOptions options)
	{
		// Draw the fold button
		DrawManipulators(graphics, false);
	}

	protected override void OnAdd()
	{
		base.OnAdd();
		EnsureTemplate();
	}

	internal void EnsureTemplate()
	{
		if (visual == null)
			OnTemplateChanged();
	}

	public static DependencyProperty TemplateProperty = DependencyProperty.Register(
		"Template", typeof(DataTemplate), typeof(MyContainerNode),
		new FrameworkPropertyMetadata(null, OnTemplateChanged));

	static void OnTemplateChanged(DependencyObject d, DependencyPropertyChangedEventArgs args)
	{
		var node = (MyContainerNode)d;
		node.OnTemplateChanged();
	}

	void OnTemplateChanged()
	{
		var template = Template;
		if (template == null)
			return;

		if (visual != null)
			RemoveVisualChild(visual);

		visual = template.LoadContent() as FrameworkElement;
		if (visual != null)
		{
			visual.DataContext = this;
			AddVisualChild(visual);
			InvalidateVisual();
		}
	}

	public DataTemplate Template
	{
		get { return (DataTemplate)GetValue(TemplateProperty); }
		set { SetValue(TemplateProperty, value); }
	}

	protected override Size MeasureOverride(Size availableSize)
	{
		if (visual != null)
			visual.Measure(Bounds.Size);

		return Bounds.Size;
	}

	protected override Size ArrangeOverride(Size finalSize)
	{
		if (visual != null)
			visual.Arrange(new Rect(Bounds.Size));
		return Bounds.Size;
	}

	protected override int VisualChildrenCount
	{
		get { return visual == null ? 0 : 1; }
	}

	protected override Visual GetVisualChild(int index)
	{
		return visual;
	}

	private FrameworkElement visual;
}
 

Code

<ResourceDictionary>
	<Style TargetType="{x:Type diag:ContainerNode}">
		<Setter Property="Template">
			<Setter.Value>
				<DataTemplate DataType="{x:Type diag:ContainerNode}">....