Code

<UserControl x:Class="TestApp.CustomControl"
	xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
	xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
	Width="50" Height="50">
	<Grid x:Name="LayoutRoot" Background="BurlyWood">
		<ComboBox Name="cmBox" Visibility="Visible"
			HorizontalAlignment="Center" VerticalAlignment="Top" Margin="0,0,0,0" Width="50" Height="30">
			<ComboBoxItem IsSelected="True" Content="1"></ComboBoxItem>
			<ComboBoxItem Content="2"></ComboBoxItem>
			<ComboBoxItem Content="3"></ComboBoxItem>
		</ComboBox>
		<TextBox Margin="0,0,0,0" Name="txBx" HorizontalAlignment="Stretch" VerticalAlignment="Bottom"
			Height="20" Padding="0" TextWrapping="Wrap">
		</TextBox>
	</Grid>
</UserControl>
 

Code

private void Diagram_SerializeControl(object sender, MindFusion.Diagramming.Silverlight.ControlNodeEventArgs e)
{
	e.Handled = true;

	e.Context.WriteBrush((e.Node.Control as CustomControl).Background, "Brush", e.XmlElement);
	e.Context.WriteInt((e.Node.Control as CustomControl).SelectedIndex, "SelectedIndex", e.XmlElement);
	e.Context.WriteString((e.Node.Control as CustomControl).Text, "Text", e.XmlElement);
}

private void Diagram_DeserializeControl(object sender, MindFusion.Diagramming.Silverlight.ControlNodeEventArgs e)
{
	e.Handled = true;
	XElement controlElement = e.XmlElement;

	Brush brush = e.Context.ReadBrush("Brush", controlElement);
	int index = e.Context.ReadInt("SelectedIndex", controlElement);
	string text = e.Context.ReadString("Text", controlElement);

	CustomControl control = new CustomControl();
	//control.ParentNode = e.Node;
	control.Text = text;
	control.SelectedIndex = index;
	control.Background = brush;

	e.Node.Control = control;
}