Rendering a non UIElement via binding

Question

If I have an object derived from System.Windows.DispatcherObject but defines a ControlTemplate.

public class A : System.Windows.DependencyObject
{
   public ControlTemplate ControlTemplate {get; set;}
}

which is a member of

public class B 
{
   public A NonUIElement {get; set;}
}

Is it possible to render this object via a Binding such as

<Border Name="Border">
<ContentPresenter Margin="5,0" Content="{Binding NonUIElement }"/>
</Border>

assuming the Datacontext of border is set to an instance of B?

TIA.

Answer 1

The object will render, but not in the way I think you're hoping for. The Content of the ContentPresenter is set to the instance of A. WPF then tries to figure out how to render this instance of A. It first asks, is this object a UIElement? In this case, the answer is no. So it next looks for a DataTemplate for the type. In this case, there's no DataTemplate for the A class. So it falls back on calling ToString(). So your ContentPresenter will display a TextBlock containing the text "YourNamespace.A".

The fact that A happens to have a member of type ControlTemplate does not affect this logic. To WPF, that's just a chunk of data that A happens to be carrying around. WPF only uses ControlTemplate when there is a Control involved and the ControlTemplate is assigned to the Template property.

So you need either to supply a DataTemplate for A (which of course can access the ControlTemplate and use it to render the instance), or create a named DataTemplate and apply that via ContentPresenter.ContentTemplate, or derive from UIElement instead.

Answer 2

This is my actual DataTemplate with binding to LayerRepresentation my challenge. LayerRepresentation could be anything so I want it to be rendered according to its ControlTemplate, if it has one.

 <HierarchicalDataTemplate DataType="{x:Type vm:MapLayerModel}" ItemsSource="{Binding Path=Children, Mode=OneTime}">
                <DockPanel Height="24" Margin="2,0" LastChildFill="False">
                    <CheckBox VerticalAlignment="Center" IsChecked="{Binding IsVisible}"/>                    
                    <Border BorderBrush="Black" BorderThickness="1">
                        <ContentPresenter 
                        Margin="5" 
                        Content="{Binding LayerRepresentation}" 
                        ContentTemplate="{Binding Path=ControlTemplate, RelativeSource={RelativeSource AncestorType={x:Type esriSymbols:Symbol}}}"    />
                    </Border>                                                                                                                                                                                                                                                                         
                    <Image 
                        x:Name="img" 
                        DockPanel.Dock="Left" 
                        Margin="0,0,4,0"
                        Source="{Binding Path=Icon, Mode=OneTime}"                                            
                        Width="16" Height="16" />                                                               
                    <TextBlock Text="{Binding Path=Name, Mode=OneTime}" Foreground="Black" VerticalAlignment="Center" DockPanel.Dock="Left" />                    
                </DockPanel>
            </HierarchicalDataTemplate>

Answer 3

I finally got it with this;

<HierarchicalDataTemplate DataType="{x:Type vm:MapLayerModel}" ItemsSource="{Binding Path=Children, Mode=OneTime}">   
**<ContentControl Margin="5" Content="{Binding LayerRepresentation}" Template="{Binding LayerRepresentation.ControlTemplate}" Mode=OneTime/>**
</HierarchicalDataTemplate>

This has been a great personal lesson on WPF templating and its content control model. Thanks again itowlson.