#1,219 – Expanding All Nodes in a TreeView by Default

Normally, when you display a TreeView, the nodes are collapsed by default and the user clicks on the expander widgets to expand nodes that they want to look at.

You can expand all nodes in the TreeView by default by setting up an ItemContainerStyle for the TreeView and specifying that you want each TreeViewItem expanded.

Below, we show the first part of a TreeView definition in XAML, referencing an ItemContainerStyle (data templates are not shown).

<TreeView Grid.Row="0" Margin="5" 
          ItemsSource="{Binding Breeds}" 
          ItemContainerStyle="{StaticResource TreeViewItemStyle_ExpandAll}" 
          HorizontalContentAlignment="Stretch">
<!-- remainder of TreeView definition goes here -->

In the style, we simply set the IsExpanded property to true.

<Style x:Key="TreeViewItemStyle_ExpandAll" TargetType="{x:Type TreeViewItem}">
    <Setter Property="IsExpanded" Value="True"/>
</Style>

Now, at runtime, all of the nodes in the TreeView are expanded by default.

#1,218 – Stretching Items in TreeView across Entire Control

You can define a custom data template for items in a TreeView, displaying any content you like in a panel, for each data item.

There’s a problem with doing this, however, if you want the container in the data template to stretch the entire width of the TreeView. In the sample below, we have a data template for a dog breed the displays data across three columns in a Grid. We’ve set the middle column up as star-sized so that the rightmost column (first letter of the breed) sits on the far right of the grid. In the TreeView, we set HorizontalContentAlignment to Stretch, to try getting this grid to stretch across the entire width of the TreeView.

        <TreeView Grid.Row="0" Margin="5" ItemsSource="{Binding Breeds}" HorizontalContentAlignment="Stretch">
            <TreeView.Resources>
                <HierarchicalDataTemplate DataType="{x:Type loc:Breed}" ItemsSource="{Binding Dogs}">
                    <Grid Margin="0,5,0,0">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto"/>
                            <ColumnDefinition/>
                            <ColumnDefinition Width="Auto"/>
                        </Grid.ColumnDefinitions>
                        
                        <TextBlock Grid.Column="0" Text="Breed:"/>
                        <TextBlock Grid.Column="1" Margin="5,0,0,0" FontWeight="Bold" Text="{Binding Name}"/>
                        <TextBlock Grid.Column="2" Margin="0,0,3,0" FontStyle="Italic" Text="{Binding FirstLetter}"/>
                    </Grid>
                </HierarchicalDataTemplate>

                <HierarchicalDataTemplate DataType="{x:Type loc:Dog}">
                    <StackPanel Orientation="Horizontal" Margin="0,2,0,0">
                        <TextBlock Text="{Binding}"/>
                    </StackPanel>
                </HierarchicalDataTemplate>
            </TreeView.Resources>
        </TreeView>

At runtime, you can see that this doesn’t work. The 3rd column is jammed up against the right side of the second column.

The problem has to do with the default ItemContainerStyle. It includes a control template for each data item that puts the main content for the data item in an auto-sized grid column, not allowing it to stretch across the control.

The solution is to override the ItemContainerStyle and tweak the column definitions to allow the content to extend across the Grid. Below is the full text of the modified style, including all dependent styles. The main style that can be used for a TreeView.ItemContainerStyle is named TreeViewItemStyle1. We’ve modified the style so that the control template has a Grid with only two columns. The second column contains the content and is star-sized.




<Style x:Key="TreeViewItemFocusVisual">
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate>
                        <Rectangle/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>




        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.Static.Checked.Fill" Color="#FF595959"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.Static.Checked.Stroke" Color="#FF262626"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.MouseOver.Stroke" Color="#FF27C7F7"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.MouseOver.Fill" Color="#FFCCEEFB"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.MouseOver.Checked.Stroke" Color="#FF1CC4F7"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.MouseOver.Checked.Fill" Color="#FF82DFFB"/>
        <PathGeometry x:Key="TreeArrow" Figures="M0,0 L0,6 L6,0 z"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.Static.Fill" Color="#FFFFFFFF"/>
        <SolidColorBrush x:Key="TreeViewItem.TreeArrow.Static.Stroke" Color="#FF818181"/>
        



<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="{StaticResource TreeViewItem.TreeArrow.Static.Fill}" Stroke="{StaticResource TreeViewItem.TreeArrow.Static.Stroke}">
                                <Path.RenderTransform>
                                    <RotateTransform Angle="135" CenterY="3" CenterX="3"/>
                                </Path.RenderTransform>
                            </Path>
                        </Border>
                        <ControlTemplate.Triggers>
                            <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="{StaticResource TreeViewItem.TreeArrow.Static.Checked.Fill}"/>
                                <Setter Property="Stroke" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.Static.Checked.Stroke}"/>
                            </Trigger>
                            <Trigger Property="IsMouseOver" Value="True">
                                <Setter Property="Stroke" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.MouseOver.Stroke}"/>
                                <Setter Property="Fill" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.MouseOver.Fill}"/>
                            </Trigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsMouseOver" Value="True"/>
                                    <Condition Property="IsChecked" Value="True"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Stroke" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.MouseOver.Checked.Stroke}"/>
                                <Setter Property="Fill" TargetName="ExpandPath" Value="{StaticResource TreeViewItem.TreeArrow.MouseOver.Checked.Fill}"/>
                            </MultiTrigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>




        


<Style x:Key="TreeViewItemStyle1" TargetType="{x:Type TreeViewItem}">
            <Setter Property="Background" Value="Transparent"/>
            <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="*"/>
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition/>
                            </Grid.RowDefinitions>
                            <ToggleButton x:Name="Expander" ClickMode="Press" IsChecked="{Binding IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" Style="{StaticResource ExpandCollapseToggleStyle}"/>
                            <Border x:Name="Bd" Grid.Column="1" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="true">
                                <ContentPresenter x:Name="PART_Header" ContentSource="Header" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            </Border>
                            <ItemsPresenter x:Name="ItemsHost" Grid.Row="1" Grid.Column="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.InactiveSelectionHighlightBrushKey}}"/>
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightTextBrushKey}}"/>
                            </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="VirtualizingPanel.IsVirtualizing" Value="true">
                    <Setter Property="ItemsPanel">
                        <Setter.Value>
                            <ItemsPanelTemplate>
                                <VirtualizingStackPanel/>
                            </ItemsPanelTemplate>
                        </Setter.Value>
                    </Setter>
                </Trigger>
            </Style.Triggers>
        </Style>



For completeness, here’s a fragment of the TreeView, using the new style.

<TreeView Grid.Row="0" Margin="5" ItemsSource="{Binding Breeds}" ItemContainerStyle="{StaticResource TreeViewItemStyle1}" HorizontalContentAlignment="Stretch">

We can see that the third element is now lined up on the right side of the TreeView at runtime.

#1,217 – Using Multiple HierarchicalDataTemplates in a TreeView

I showed last time how to use a HierarchicalDataTemplate as the ItemTemplate for a TreeView. This allowed us to specify the look and feel of each node in the tree and also dictated how the main data item would be traversed to generate the tree.

If you have some hierarchical data in which the items are not all of the same type, you can specify more than one HierarchicalDataTemplate for the TreeView, based on the underlying type of each node.

Let’s assume that we have both a Breed and a Dog class. Breed objects contain information about a breed and in turn have a Dogs property that is a list of individual dogs of that breed.

In the example below, we have a TreeView whose ItemsSource is bound to a list of breeds. We then include a template to use for each Breed item and a different template to use for each Dog item in the tree. We also indicate that the tree should be expanded by looking at the Dogs property in each breed instance.

        <TreeView Grid.Row="0" Margin="5" ItemsSource="{Binding Breeds}">
            <TreeView.Resources>
                <HierarchicalDataTemplate DataType="{x:Type loc:Breed}" ItemsSource="{Binding Dogs}">
                    <StackPanel Orientation="Horizontal" Margin="0,5,0,0">
                        <TextBlock Text="Breed:"/>
                        <TextBlock Margin="5,0,0,0" FontWeight="Bold" Text="{Binding Name}"/>
                    </StackPanel>
                </HierarchicalDataTemplate>

                <HierarchicalDataTemplate DataType="{x:Type loc:Dog}">
                    <StackPanel Orientation="Horizontal" Margin="0,2,0,0">
                        <TextBlock Text="{Binding}"/>
                    </StackPanel>
                </HierarchicalDataTemplate>
            </TreeView.Resources>
        </TreeView>

Note that we specify a DataType for each HierarchicalDataTemplate. As the tree is constructed, the appropriate template will be used, based on whether a node is a breed or a dog.

Below, we can see how this will look at runtime. Breed nodes show the breed’s name. Dog nodes show the dog’s name and age. We just have a TextBlock bound to the Dog instance as a whole, which causes the dog’s ToString method to get invoked. In our case, we’ve overridden ToString to display the dog’s name and age.

#1,216 – Creating a Custom ItemTemplate in a TreeView

If we just want each node in a TreeView control to contain text, we can use a single TreeViewItem in the HierarchicalDataTemplate and bind its Header property to the text that we want displayed. However, we can use an Panel we like in the data template.

The example below builds on our last post, but using a Grid in a Border for each person in the tree.

<TreeView Grid.Row="0" Margin="5" ItemsSource="{Binding Royal}">
    <TreeView.ItemTemplate>
        <HierarchicalDataTemplate ItemsSource="{Binding Children}">
            <Border Background="AliceBlue" Margin="0,2,0,0" Padding="4,2,8,2" 
                    BorderBrush="DimGray" BorderThickness="1"
                    CornerRadius="3">
                <Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition/>
                        <RowDefinition/>
                    </Grid.RowDefinitions>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition/>
                        <ColumnDefinition/>
                    </Grid.ColumnDefinitions>

                    <TextBlock Grid.Row="0" Grid.Column="0" FontWeight="Bold"
                               Text="{Binding Name}"/>
                    <TextBlock Grid.Row="1" Grid.Column="0" FontStyle="Italic"
                               Text="{Binding BirthDeath}" Margin="5,0,0,0"/>
                    <Image Grid.RowSpan="2" Grid.Column="2"
                           Height="20" Width="20" Margin="5,0"
                           Source="Crown.png"
                           Visibility="{Binding KingOrQueen, Converter={StaticResource BooleanToVisibilityConverter}}"/>
                </Grid>
            </Border>
        </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

Here’s what the final result looks like (after I expand a few of the TreeView nodes: