TreeView in ControlTemplate - Handling Item Expanded

Kevin Marois

I am creating a Custom Control and in the control template I have a TreeView class in it.

<Setter Property="Template">

    <Setter.Value>

        <ControlTemplate TargetType="{x:Type local:MyControl}">

            <Border Background="{TemplateBinding Background}"
                BorderBrush="{TemplateBinding BorderBrush}"
                BorderThickness="{TemplateBinding BorderThickness}">

                <TreeView ItemsSource="{Binding TreeDataItems, RelativeSource={RelativeSource TemplatedParent}}">

                    <TreeView.Resources>
                        <HierarchicalDataTemplate DataType="{x:Type local:TreeItem}" ItemsSource="{Binding Children}">
                            <TextBlock Text="{Binding Path=Caption}" />
                        </HierarchicalDataTemplate>
                    </TreeView.Resources>

                    <i:Interaction.Triggers>
                        <i:EventTrigger EventName="TreeViewItem.Expanded">
                            <i:InvokeCommandAction Command="{Binding TreeItemExpandedCommand, RelativeSource={RelativeSource TemplatedParent}}"
                                                CommandParameter="{Binding}">

                            </i:InvokeCommandAction>
                        </i:EventTrigger>
                    </i:Interaction.Triggers>

                </TreeView>
            </Border>

        </ControlTemplate>

    </Setter.Value>

</Setter>

</Style>

In the code behind I have

private ICommand _TreeItemExpandedCommand;
public ICommand TreeItemExpandedCommand
{
get
{
if (_TreeItemExpandedCommand == null)
_TreeItemExpandedCommand = new RelayCommand(p => TreeItemExpandedExecuted(p));
return _TreeItemExpandedCommand;
}
}

private void TreeItemExpandedExecuted(object args)
{
}

When I expand a node nothing happens. There are no binding errors, and the Command's getter fires when it starts, but the TreeItemExpandedExecuted never fires.

I tried using the event itself:

...

and

private void TreeViewItem_Expanded(object sender, RoutedEventArgs e)
{