WPF TreeView: hide expand sign for all the leaf nodes - wpf

Question

How to hide the expand/collpse sign for leaf nodes in a WPF TreeView?
In other words: how to make leaf nodes automatically expand?
Any way to achive this using XAML?
Thanks,

Answer 1

Similar to other answers, to Expand all nodes you can just use
<TreeView >
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsExpanded" Value="True" />
</Style>
</TreeView.ItemContainerStyle>
This will make all TreeViewItems automatically Expand. However, you'll still see the Expand/Collapse ToggleButton. To get rid of that one you'll have to re-template TreeViewItem like this
<TreeView ...
ItemContainerStyle="{StaticResource TreeViewItemExpandedStyle}">
And the Style (pretty much Xaml)
<Style x:Key="TreeViewItemExpandedStyle" TargetType="{x:Type TreeViewItem}">
<Setter Property="Background" Value="Transparent"/>
<Setter Property="IsExpanded" Value="True"/>
<Setter Property="HorizontalContentAlignment" Value="{Binding HorizontalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
<Setter Property="VerticalContentAlignment" Value="{Binding VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
<Setter Property="Padding" Value="1,0,0,0"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
<Setter Property="FocusVisualStyle" Value="{StaticResource TreeViewItemFocusVisual}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TreeViewItem}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition MinWidth="19" Width="Auto"/>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition/>
</Grid.RowDefinitions>
<ToggleButton x:Name="Expander" IsEnabled="False" Visibility="Hidden" ClickMode="Press" IsChecked="{Binding IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" Style="{StaticResource ExpandCollapseToggleStyle}"/>
<Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.Column="1" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="true">
<ContentPresenter x:Name="PART_Header" ContentSource="Header" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
</Border>
<ItemsPresenter x:Name="ItemsHost" Grid.ColumnSpan="2" Grid.Column="1" Grid.Row="1"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsExpanded" Value="false">
<Setter Property="Visibility" TargetName="ItemsHost" Value="Collapsed"/>
</Trigger>
<Trigger Property="HasItems" Value="false">
<Setter Property="Visibility" TargetName="Expander" Value="Hidden"/>
</Trigger>
<Trigger Property="IsSelected" Value="true">
<Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}"/>
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsSelected" Value="true"/>
<Condition Property="IsSelectionActive" Value="false"/>
</MultiTrigger.Conditions>
<Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
</MultiTrigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
<Trigger Property="VirtualizingStackPanel.IsVirtualizing" Value="true">
<Setter Property="ItemsPanel">
<Setter.Value>
<ItemsPanelTemplate>
<VirtualizingStackPanel/>
</ItemsPanelTemplate>
</Setter.Value>
</Setter>
</Trigger>
</Style.Triggers>
</Style>
<Style x:Key="TreeViewItemFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<PathGeometry x:Key="TreeArrow" Figures="M0,0 L0,6 L6,0 z"/>
<Style x:Key="ExpandCollapseToggleStyle" TargetType="{x:Type ToggleButton}">
<Setter Property="Focusable" Value="False"/>
<Setter Property="Width" Value="16"/>
<Setter Property="Height" Value="16"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border Background="Transparent" Height="16" Padding="5,5,5,5" Width="16">
<Path x:Name="ExpandPath" Data="{StaticResource TreeArrow}" Fill="Transparent" Stroke="#FF989898">
<Path.RenderTransform>
<RotateTransform Angle="135" CenterY="3" CenterX="3"/>
</Path.RenderTransform>
</Path>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Stroke" TargetName="ExpandPath" Value="#FF1BBBFA"/>
<Setter Property="Fill" TargetName="ExpandPath" Value="Transparent"/>
</Trigger>
<Trigger Property="IsChecked" Value="True">
<Setter Property="RenderTransform" TargetName="ExpandPath">
<Setter.Value>
<RotateTransform Angle="180" CenterY="3" CenterX="3"/>
</Setter.Value>
</Setter>
<Setter Property="Fill" TargetName="ExpandPath" Value="#FF595959"/>
<Setter Property="Stroke" TargetName="ExpandPath" Value="#FF262626"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 2

Bind the TreeViewItems to an ObservableCollection and leave the ObservableCollection empty. That way the expand/collapse sign is not shown since the UI knows there is nothing to expand. Here is the relevant part from some of my code:
XAML:
<TreeView x:Name="TreeView"
ItemsSource="{Binding TopLevelNodes}"
VirtualizingStackPanel.IsVirtualizing="True"
VirtualizingStackPanel.VirtualizationMode="Recycling">
<TreeView.Resources>
<HierarchicalDataTemplate
DataType="{x:Type local:ViewModel}" ItemsSource="{Binding Children}">
ViewModel:
ObservableCollection<ObjectBaseViewModel> _children;
public ObservableCollection<ObjectBaseViewModel> Children
{
get
{
if (_children == null)
_children = new ObservableCollection<ViewModel>();
return _children;
}
}

Answer 3

I don't know about a pure XAML solution but you could bind the IsExpanded property of the TreeviewItem and have this property on your leaf nodes set to true by default (you don't have to have this property at all on other nodes.
<Style TargetType="controls:TreeViewItem">
<Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}"></Setter>
</Style>

Answer 4

Firstly set IsExpanded to true
<Style x:Key="{x:Type TreeViewItem}"
TargetType="{x:Type TreeViewItem}">
<Setter Property="IsExpanded"
Value="True" />
Then hide the Expander
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TreeViewItem}">
<ControlTemplate.Triggers>
<Trigger Property="HasItems"
Value="false">
<Setter TargetName="Expander"
Property="Visibility"
Value="Hidden" />
</Trigger>
<Trigger Property="HasItems"
Value="true">
<Setter TargetName="Expander"
Property="Visibility"
Value="Hidden" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
A very good reason to use a treeview rather than a datagrid with rowdetails is that the up and down arrow keys traverse from expanded details to header details seamlessly.