Question

The company has the traditional complex organizational structure, defining the amount of levels using the letter ‘n’ rather than an actual number. I will try and express the structure I’m trying to achieve in mono-spaced font:

         Alice  ,--------|-------,------,------, Bob      Fred    Jack   Kim    Lucy  |        |       Charlie  Greg     Darren   Henry Eric 

As you can see it’s not symmetrical, as Jack, Kim and Lucy report to Alice but have no reports of their own.

Using a TreeView with an ItemsPanel containing a StackPanel and Orientation='Horizontal' is easy enough, but this can result in a very large TreeView once some people have 20 others reporting to them! You can also use Triggers to peek into whether a TreeViewItem has children with Property='TreeViewItem.HasItems', but this is not in the same context as the before-mentioned ItemsPanel. Eg: I can tell that Fred has reports, but not whether they have reports of their own.

So, can you conditionally format TreeViewItems to be Vertical if they have no children of their own?

Answer 1

I did end up using tips from the linked article, which I’d already read through but didn’t think would help me.

The meat of it happens here, in a converter:

<ValueConversion(GetType(ItemsPresenter), GetType(Orientation))> _ Public Class ItemsPanelOrientationConverter Implements IValueConverter  Public Function Convert(ByVal value As Object, ByVal targetType As System.Type, _ ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) _ As Object Implements System.Windows.Data.IValueConverter.Convert      'The 'value' argument should reference an ItemsPresenter.'     Dim itemsPresenter As ItemsPresenter = TryCast(value, ItemsPresenter)     If itemsPresenter Is Nothing Then         Return Binding.DoNothing     End If      'The ItemsPresenter''s templated parent should be a TreeViewItem.'     Dim item As TreeViewItem = TryCast(itemsPresenter.TemplatedParent, TreeViewItem)     If item Is Nothing Then         Return Binding.DoNothing     End If      For Each i As Object In item.Items         Dim element As StaffMember = TryCast(i, StaffMember)         If element.IsManager Then             'If this element has children, then return Horizontal'             Return Orientation.Horizontal         End If     Next      'Must be a stub ItemPresenter'     Return Orientation.Vertical  End Function 

Which in turn gets consumed in a style I created for the TreeView:

    <Setter Property='ItemsPanel'>         <Setter.Value>             <ItemsPanelTemplate >                 <ItemsPanelTemplate.Resources>                     <local:ItemsPanelOrientationConverter x:Key='conv' />                 </ItemsPanelTemplate.Resources>                 <StackPanel IsItemsHost='True'                              Orientation='{Binding                                RelativeSource={x:Static RelativeSource.TemplatedParent},                              Converter={StaticResource conv}}' />             </ItemsPanelTemplate>         </Setter.Value>     </Setter>